School Science Lessons
2024-06-19
Chemistry, Aa to Ac
Contents
AAS Atomic Absorption Spectroscopy
Abbreviations Chemistry
Abbreviations English language
Absolute zero, Kelvin scale
Absorption spectrum, Sodium, (Experiment)
Abietic acid
Abscisic acid
Absinthin
Absolute alcohol ethanol, (Experiments)
Absolute zero Kelvin scale
Abuse of volatile substances
Acacetin
Acanthicifoline
Acanthosides
Acaricides, (Agriculture)
Accumulator Lead accumulator cell, (Experiments)
Accuracy and error Errors
Acerosin
Acephate
Acesulfame
Acetal
Acetaldehyde, (Experiments)
Acetates, Ethanoates
Acetyl group, −COCH3, −C(=O)−CH3, Ac, ethanoyl, (Wikipedia)
Acetylharpagide
Acetylene, Ethyne, (Experiments)
Acetamide, (Experiments)
Acetaminophen, Paracetamol, (Experiment)
Acetamiprid, C10H11ClN4, Neonicotinoid insecticide
Acetic acid, Ethanoic acid
Acetic alcohol, Prepare, (Experiment)
Acetic anhydride
Aceto-alcohol, Prepare
Aceto-carmine, Prepare
Aceto-orcein, Prepare
Acetoacetic acid, (Experiment)
Acetochlor, (Agriculture)
Acetone, (Experiments)
Acetone peroxide, TATP
Acetonitrile
Acetosyringone
Acetyl chloride
Acetyl eugenol, Eugenol acetate
Acetylcholine
Acetylides
Acetyldigoxin
Acetylene, Ethyne
Acetylpyrrolidine,
Acetylpyrroline
Acetylsalicyclic acid, Aspirin
Achillin
Acid anhydrides
Acid fuchsin
Acid rain
Acidity
Acids acid-, acids, acidic, acidify, (Experiments)
Acolongifloroside K
AconineH
Aconitine
Aristolochic acid
Acridine
Acriflavine
Acrilan (trade name)
Acroleic acid
Acrolein
Acronidine
Acrylates
Acyl halide
Acryl polymer (Experiments)
Acrylonitrile (Experiments)
Acrylamide
Acrylic acid propenoic acid, (Experiment)
Acrylic glass Polymethyl methacrylate, (Experiments)
"Acrylics"
Actinides, actinoids
Actinidine
Actinium, Ac
Actinolite, (Geology)
Activated carbon activated charcoal
Active constituent (Pesticides label)
Activity series of metals as reducing agents
Acute toxicity
Acyl halide
Acyclic hydrocarbons
Abbreviations
i.e. (id est) means "that is" or "in other words".
e.g. (exempli gratia) means "for example".
viz. (videlicet) means "namely" or "that is to say".
et al. (et alii) means "and others" or "and collaborators".
q.v. (quod vide) means "which to see", written after words to be looked up in the current document. ibid. (ibidem) means "in the same place", refers to a previously listed work.
cf. (confer) means to see a given citation for comparison.
Acerosin
Acerosin, C18H16O8, is a trimethoxyflavone metabolite.
It occurs in Scoparia dulcis, Iva acerosa, Helianthus, Gardenia, Vitex, and in peel of mandarin orange Citrus reticulata.
Acesulfame
Acesulfame, C4H5NO4S is a sulfamate ester, irritant, sweetening agent, and environmental contaminant.
Food code E950, Acesulphame Potassium, Acesulfame-K, Ace-K, C4H4KNO4S, synthetic chemical, artificial sweetener, Health risk, tumours
Food code E962, salt of aspartame-acesulfame, artificial sweetener, emulsifier, stabilizer, thickener and gelling agent, Health risk, tumours
19.6.3 Cola, Diet or Light contents
Acetaldehyde
Acetaldehyde C2H4O, C2H4O, CH3CHO, ethanal, is a colourless liquid, choking odour, BP 21°C, vapour irritates eyes, tobacco smoke carcinogen.
Prepare ethanal with potassium dichromate
Prepare ethanal with potassium manganate (VII)
Acetamide
Acetamide, CH3CONH2, C2H5NO, ethanamide, acetic acid amide, is colourless crystals, mouse odour, low toxicity, but may cause skin irritation.
It is formed from condensation of acetic acid with ammonia, and it is used as solvent.
Amide RCONH2, (amine + acid), No prefix
Suffix, -oic, Suffix, -amide, e.g. acetamide = ethanamide, CH3CONH2
Amides
Heat energy changes solid to liquid
Latent heat of fusion of ice to water,/a>
Acetates
Acetates, CH3COO-, Ethanoates
An acetate (ethanoate) is a salt or ester of acetic acid (ethanoic acid).
An acetate as a salt: Sodium acetate (sodium ethanoate), CH3COONa.
An acetate as an ester: Ethyl acetate, (ethyl ethanoate), CH3COO(C2H5).
If acetate is shown as OAc−, acetic acid is shown as HOAc.
Weak acids, e.g. ethanoic acid (acetic acid, CH3COOH, carbonic acid and sulfurous acid dissociate very little in aqueous solution.
However, their salts, e.g. potassium acetate CH3COOK are completely dissociated into ions.
Acetic anhydride, (CH3CO)2O
Celluloid
Cellulose acetate, Cellulose triacetate
Experiments
12.3.9 Acids with salts
Dancing mothballs
17.3.5 Ethyl acetate with sodium hydroxide
16.4.2 Prepare ethyl acetate
Acanthosides
Acanthoside B, Eleutheroside e1, C28H36O13, syringaresinol beta-D-glucoside
It occurs in Eucommia ulmoides bark, in Acanthopanax sessiliflorus roots
Acanthoside D, Syringaresinol-di-O-glucoside, Liriodendrin, C34H46O18, is a beta-D-glucoside, antioxidant, anti-inflammatory, stress relieving.
It occurs in Acanthopanax sessiliflorus roots, Eleutherococcus senticosus, Liriodendron bark, Penstemon
Cinnamyl acetate
Cinnamyl acetate, C11H12O2, CH3CO2CH2CH=CH(C6H5), (from condensation of cinnamyl alcohol + acetic acid), is a fragrance ingredient, in chewing gum.
It occurs in Chinese cinnamon leaf oil, and Nicotiana species.
Ethoxyethanol C4H10O2
Ethyl ethanoate
Sodium acetate, Ethyl ethanoate as a salt
Ethyl ethanoate Ethyl ethanoate as an ester
Ethyl ethanoate
Lead (II) acetate C4H6O4Pb, CH3COO)2Pb, lead (II) ethanoate
Medroxyprogesterone acetate, Depo-Provera contraceptive
Copper (II) acetoarsenite, Paris Green
Polyvinyl acetate
Tests for acetates
Acetic anhydride
Acetic anhydride, (CH3CO)2O, ethanoic anhydride, acetic acid anhydride, acetyl oxide, acetic oxide,
Use < 25 mL or g in a fume cupboard or a well-ventilated area
Solution < 8%, Not hazardous, i.e. 8% acetic acid
It is a highly volatile liquid, irritating odour, reacts with moisture in air, corrosive to skin, strong respiratory irritant.
(CH3CO)2O + H2O --> 2 CH3COOH
acetic anhydride + water --> acetic acid
Prepare acetate esters from alcohols by reaction with acetic anhydride.
Reactions with alcohols, oxides, permanganates, nitric acid may be hazardous to explosive. Be careful!
Acetoacetic acid
Acetoacetic acid, C4H6O3, CH3COCH2COOH, 3-oxobutanoic acid, is a fatty acid
It occurs in Phaseolus vulgaris, and Apium graveolense.
Ethyl acetoactonate
Keto acids
Experiment
Tests for ketones
Acetone
Cleaning agents, solvents
Boiling point of inflammable liquids
Bromination of acetone
Potassium dichromate as an oxidizing agent, (See 5.)
Experiments
Solvent extraction of oil from peanuts
Oxidation of acetone vapour, copper catalyst
Acetone
Acetone, CH3COCH3, 2-propanone, propanone, dimethyl ketone, is highly flammable, characteristic irritant vapour, slightly toxic if ingested
Use low cost, technical grade acetone, from hardware store, as solvent, and to clean glassware.
Acetone ACS reagent, 99.5%, clear colourless volatile liquid, characteristic smell, inflammable
RD 0.79 gm cm-3, BP 56.5oC, miscible with water and ether, and oils sharp sweet taste
Acetone is a curing agent for epoxy resin adhesives, surface coating, irritant.
Use acetone in a fume cupboard or use < 50 mL in a well-ventilated area.
Acetone react violently with chloroform.
Use ethyl acetate or methyl isobutyl ketone as alternative solvent to acetone.
Heat acetone on a water bath, NOTon a naked flame.
Acetone dissolves polystyrene packing pieces rapidly by dissolving the linking units.
Common names, Nail polish remover, (but not in Australia), e.g. "Cutex", nail paint remover, paint thinner, may be sold as "pure acetone".
Junior secondary students should use acetone only as a cold solvent, and they should NOTreact or heat acetone.
Acetonitrile
See diagram, Acetonitrile
Acetonitrile, CH3CN, (acetonitrilo), cyanomethane, methyl cyanide, flammable, colourless liquid, sweet ether-like odour, simplest organic nitrile, Toxic if ingested
Acetonitrile, Solution < 3%, Not hazardous
Acronitrile is used in C3H3N acrylics (plastics), vinyl cyanide, cyanoethylene, synthetics, paint.
Indole-3-acetonitrile, C10H8N2
Acetosyringone
Acetosyringone, C10H12O4, is a phenol, irritant, a non-steroidal anti-inflammatory drug, an anti-asthmatic drug, a non-narcotic analgesic.
It occurs in Justicia adhatoda, Polyporus umbellatus, in Saccharomyces cerevisiae.
It occurs in Nicotiana tabacum root cultures, exuded from roots, to cause infection by Agrobacterium tumefaciens.
Tobacco plant, (Nicotiana tabacum)
Acetoxychavicol acetate
Acetoxychavicol acetate, C13H14O4, is a galangal acetate, an acetate ester, a phenylpropanoid, and an antineoplastic agent.
It occurs in herbs and spices, sweet flag, Acorus calamus, Alpinia galanga, and in Apis cerana.
Snap ginger, (Alpinia calcarata)
Acetoxyeugenol acetate
Acetoxyeugenol acetate, C14H16O5, is a phenylpropanoid, a monomethoxybenzene
It occurs in Alpinia galanga.
Snap ginger, (Alpinia calcarata)
Acetylbrowniine
Acetylbrowniine, C27H43NO8, 14-O-Acetylbrowniine, is an acetate ester obtained by acetylation of browniine, C25H41NO7.
Delphinium oreophilum
Acetyl chloride
Acetyl chloride, C2H3ClO, CH3COCl, C2ClH3O, ethanoyl chloride, acyl chloride, acetic chloride, has low flash point.
It is toxic by all routes, colourless, fuming liquid, pungent odour, vapour heavier than air, irritates eyes and mucous membranes, corrodes metals.
Acetylcholine
Acetylcholine C7H16NO2+, is a neurotransmitter stimulates muscle, acetyl ester of choline, major transmitter at neuromuscular junctions.
It occurs in fruit and seed of breadfruit
9.0 Fruit and seed, (See: 4. Acetylcholine)
Atropine C17H23NO3, alkaloid
Nicotine C10H14N2, alkaloid
Nicotine, C10H14N2, tobacco smoking and chewing
Acetylharpagide
Acetylharpagide, C17H26O11, 8-O-Acetylharpagide, iridoid glucoside, ecdysteroid,
It is a Chinese medicine, anti-inflammatory, vasoconstrictor, antibacterial, antiviral, acts on smooth. muscle, inhibits, Epstein-Barr virus (EBV),
It occurs in Ajuga decumbens, and Ajuga reptans
Acetylpyrrolidine
Acetylpyrrolidine, C6H11NO, 2-Acetylpyrrolidine
Substituted pyrrolidine, CH3COC5H4N, occurs in malt, popcorn, and beer
Acetylpyrroline
Acetylpyrroline, C6H9NO, 2-Acetyl-1-pyrroline (2AP), is in white bread smell in cereals, hot popcorn, jasmati and basmati rice, wheat bread crust, sweet corn
It occurs in Screwpine
Acids
Acid acid-, acids, acidic, acidify, acidity
Acid anhydrides
Andrade's acid fuchsin, indicator
Acid-base indicators
Acid rain
Acidic oxides (Experiments)
Acidity
1.1 Acids, List of mineral acids
1.2 Acids, List of organic acids
Acids with
Prepare acids
Acids, Chemical reactions
Acids
Acids in foods, Food acids
Acids with other substances, (Experiments)
Acidulated water, Cooking
Carbonic acid, soda water
Concentrated acids with a non-metal, carbon
Concentrated acids with metals, sulfuric acid with copper
Hydrochloric acid
Phosphoric acid
Properties of acids
Nitric acid, HNO3
Nitrous acid, HNO2
Reactions of sulfuric acid
Reactions of dilute acids
19.1.1Solid acids, solubility
Tastes of acids
Tests for acid radicals in solution
5.6.0 Acid-base indicators
Acid-base reactions
Acid dissociation constant at logarithmic scale, pKa
Experiments
Acid-base indicators in the home
Acid-base neutralization, acid with base forms a salt and water
Butyl chloride rainbow reactions
pH of solid acids
Solid acids, add sodium carbonate
Solid acids, solubility
Taste of acids , solid acids in the home
Titration.
Acidity
Acidity, definition, [degree of being an acid]
Acidity and alkalinity
Acidity of vinegar and wine
Acidity regulators, food additives
Acidity test milk testing
Soil acidity
Prepare acids
Prepare acid-base indicators
Prepare acid alcohol solution
Prepare acids and bases, dilution instruction
Prepare dilute acids
Prepare dilute acids and bases, (Safety instructions)
19.1.17 Solid acids, solubility
Shake different solid acids in separate test-tubes half filled with water.
Which of the acids are the most soluble and the least soluble in water?
Citric acid
Tartaric acid
Boric acid
Acid rain
Acid rain is rain made acidic by atmospheric pollution.
Acid rain and nitrogen oxides, NOx
Acid rain, SOx, from burning sulfur or sulfur compounds
Air pollution
CFCs, chlorofluorocarbons, "Freons"
Acidic oxides
Acidic oxides
Carbon dioxide, acidic oxides (non-metal oxides)
Carbon dioxide with barium hydroxide solution
Carbon dioxide with sodium hydroxide solution
12.3.8 Dilute acids with acidic oxides (non-metal oxides)
Reactions of oxides
An acidic oxide is oxide of a nonmetal, e.g. carbon dioxide, or a metal in high oxidation state, e.g. chromium trioxide, CrO3
Acidic oxides do not react with acids.
Acidic oxides form when a nonmetal burns.
Acidic oxides are usually gases at room temperature, e.g. CO2, NO2, SO2, SO3.
Acidic oxide + base --> salt + water
CO2 (g) + NaOH (aq) --> Na2CO3 (s) + H2O (l)
Acidic anhydride is an acidic oxide which reacts with water to form a base.
CO2 + H2O --> H2CO3 (carbonic acid)
SO3 (g) + H2O --> H2SO4 (aq) (sulfuric acid)
Acids with other substances
Acids with sodium bicarbonate
Acids with sodium carbonate
Acids with sodium thiosulfate
Acids with zinc
Acids with aluminium
Concentrated acids with metals, nitric acid with copper
Concentrated acids with a non-metals, carbon
Dilute acids with
Dilute acids with acidic oxides, non-metal oxides
Dilute acids with amphoteric oxides
Dilute acids with basic oxides, copper (II) oxide
Dilute acids with calcium hydrogen carbonate
Dilute acids with carbonates, common carbonates
Dilute acids with hydroxides, magnesium hydroxide
Dilute acids with hydroxides, sodium hydroxide
Dilute acids with metals, hydrochloric acid
Dilute acids with metals, sulfuric acid, hydrochloric acid, ethanoic acid
Dilute acids with metals, sulfuric acid with steel wool
Dilute acids with non-metals, carbon, sulfur
Dilute acids with salts
Dilute acids with sodium hydrogen carbonate
Dilute acids with sodium hydroxide
Dilute hydrochloric acid with hydroxides
Dilute hydrochloric acid with sodium carbonate
Dilute nitric acid with copper
Dilute sulfuric acid with aluminium
Dilute acids with common carbonates
Dilute hydrochloric acid with calcium carbonate
Dilute hydrochloric acid with sodium carbonate
Dilute sulfuric acid with calcium carbonate
Dilute tartaric acid with egg shell, soil, wood ash
Dilute tartaric acid with sodium carbonate
Dilute hydrochloric acid with sodium carbonate
Sulfuric acid with copper
Acridine
Acridine, C13H9N, toxic if ingested and skin contact, give First aid if ingested: Give water, and induce vomiting
See diagram, Acridine, (9-Azaanthracene), (2,3-Benzoquinoline)
Acridine orange, C17H19N3, an aminoacridine, hydrochloride salt 'acridine orange', is used to stain cell nuclei, e.g. DNA.
Acriflavine, C14H14ClN3, orange-brown, dye and antiseptic, derived from acridine
It shows green fluorescence when diluted in water.
Acroleic acid
Acroleic acid, CH2CHCO2H, C3H4O2, acrylic acid, propenoic acid, prop-2-enoic acid, Toxic, the simplest unsaturated carboxylic acid
Acroleic acid, Solution < 5%, Not hazardous, Corrosive, colourless liquid with an acrid odour
It is used in polishes, paints, coatings, rug backings, adhesives, plastics, textiles, and paper
Polyacrylic acid, cross-linked sodium salt
Polyacrylic acid, water-soluble polyelectrolyte, is used to increase building substances viscosity
Polyacrylamide powder, superabsorbent, is used to make toy product "Instant Wet Expanding Snow"
Sodium polyacrylate gels, ghost crystals, Prepare
Sodium polyacrylate, (C3H3NaO2)n, waterlock, is sold as toy product "Super Expanding Creatures"
Acrolein
Acrolein, C3H4O, CH2=CHCHO, prop-2-enal, ethylene aldehyde, acrylic aldehyde, aqualin, Magnacid, Toxic by all routes
Acrolein, Solution < 0.1%, Not hazardous, clear, yellowish liquid, sweet, pungent burnt fat smell, highly flammable, volatile organic compound, unstable
It polymerizes in the presence of light or alkali, or strong acids.
It occurs in cigarette smoke and vehicle exhaust, aquatic herbicide, kill algae and waterweeds.
Tests for glycerol
Acrylates
Acrylates, CH2=CHCOO−, prop-2-enoates, salts or esters or bases of acrylic acid
Esters of acrylic acid are commonly called acrylates, e.g. methyl acrylate, CH2=CHCOOCH3
Mixture of acrylates, acrylate polymer, is a viscous liquid used as thickener in personal products
Acrylic acid
Acrylic acid, CH2CHCOOH, C3H4O2, CH2=CHCOOH, 2-Propenoic acid, colourless liquid, distinct acrid odour, corrosive to metals and tissue If heated in a closed container a violent rupture may occur. Acrylic acid, CH2CHCOOH, "acrylics"
Butter, butter oil, clarified butter, ghee, (See, 6.)
Tests for glycerol
Acrolein
Acrolein, CH2CHCHO, CH2=CHCHO, C3H4O, acrylaldehyde, 2-Propenal, the simplest unsaturated aldehyde, colourless or yellow liquid, toxic chemical
It has a horrible odour like the smell of burnt fat when glycerol breaks down into acrolein.
It is used as a pesticide.
Acrolein test for presence of fats: Heat sample with potassium bisulfate --> acrolein released
Acrylonitrile
Acrylonitrile, CH2=CH-CN, flammable, low flashpoint, below 32oC, poison, used to manufacture acrylic acid
Acryl polymer, generic name for fibres > 85% acrylonitrile units
ABS mixed polymer, acrylonitrile, butadiene, styrene, thermoset plastics: 3.7.28, Polypropenonitrile
Nitriles: 16.2.4.2
Experiments
Acrylonitrile-butadiene-styrene, burning test for synthetic fibres
Chewing gum, (Tg)
Actinium, Ac
Actinium RSC
Actinium, Ac, (Greek actinray), refers to light causing chemical change, radioactive, no commercial use.
Actinium, Table of Elements
White radioactive metal, emits a pale blue light, forms coating of actinium oxide to prevent further chemcal reactions
Traces of isotope 227Ac are found in uranium and thorium ores.
12.3.0H Properties of acids
Acids are good electrolytes, react with active metals, turn blue litmus red, and have a sour taste.
Dilute acids contain hydrogen ions in aqueous solution.
You can represent the hydrogen ion, which is really a proton, in different ways to show how it is related to the water molecules in the solution.
You can show it as the hydrated hydrogen ion, [proton, H+(aq)], or as the hydronium ion [oxonium ion, H3O+(aq)]
However, for convenience, use H+(aq).
Concentrated sulfuric acid exists mainly as H2SO4 molecules.
Hydrochloric acid and nitric acid dissociate into ions even in concentrated solution.
Weak acids, e.g. ethanoic acid, acetic acid, CH3COOH carbonic acid and sulfurous acid dissociate very little in aqueous solution.
However, their salts, e.g. potassium acetate CH3COOK, are completely dissociated into ions.
Using the Bronsted-Lowry definition of acids and bases, an acid donates a proton (H+) to another substance and a base accepts a proton from another substance.
When sulfuric acid dissociates in water it donates a proton (H+) to the water molecule.
So in this reaction the water molecule acts as a base.
H2SO4 + H2O --> HSO4-+ H3O+
When ammonia dissolves in water, ammonia accepts a proton and so it is the base.
So in this reaction the water molecule acts as an acid
NH3 + H2O < --> NH4++ OH-
12.3.0.1 Amphoteric substances can act as an acid or a base.
In the above reactions water is acting as a base with sulfuric acid and is acting as an acid with ammonia.
Similarly, bicarbonate ion can act as an acid to donate a proton to form the carbonate ion.
HCO3-+ H2O < --> CO32-+ H3O+
Also, bicarbonate ion can act as a base to accept a proton to form carbonic acid.
HCO3-+ H2O < --> H2CO3 + OH-
12.3.0.2 Polyprotic acids can donate more than one proton, e.g. carbonic acid.
H2CO3 + H2O < --> HCO3-+ H3O+ (The first proton to be donated to a water molecule.)
HCO3-+ H2O < --> CO32-+ H3O+ (The second proton to be donated to a water molecule.)
Quinacrine
Quinacrine, C23H30ClN3O, Mepacrine, Atabrine, is an acridine derivative, bright yellow powder, odourless
It can be toxic, kills protozoa, antihelminthic, used to treat giardiasis.
During World War II in the pacific region it was widely used as antimalarial drug known as Atebrine.
Itt was unpopular with Australian troops fighting in Papua New Guinea, because it turned skin yellow it and was supposed to make men infertile.
Atebrine was generally replaced by chloroquine, C18H26ClN3, but Plasmodium falciparum has developed resistance to it.
12.3.0.3 Strong acids and weak acids
A strong acid completely dissociates into ions, e.g. nitric acid has almost complete dissociation, 93%.
HNO3 (aq) + H2O H3O+(aq) + NO3-(aq)
A weak acid only partly dissociates into ions, e.g. acetic acid.
CH3COOH + H2O < --> CH3COO-+ H3O+
Describing acids and bases as strong or weak only refers to their reaction with water and not the concentration or the number of moles in a volume.
The strong acids include:
Perchloric acid HClO4, hydrochloric acid HCl, hydrobromic acid HBr, hydroiodic acid (hydriodic acid), HI, nitric acid HNO3, and sulfuric acid H2SO4.
Any other acid is a weak acid, because it does not completely dissociate in water.
12.3.0.3a , Acid dissociation constant
The acid dissociation constant, Ka of the acid HB,
HB (aq) <--> H+(aq) + B-(aq)
Ka = [H+][B-] / [HB]
Ka is a measure of the degree to which an acid or base will dissociate in water.
Stronger acids have a larger Ka and a smaller pKa than weaker acids.
The greater the value of Ka, the more the formation of H+ is favoured, and the lower the pH of the solution.
12.3.0.3b Acid dissociation constant at logarithmic scale, pKa
pKa = -log10Ka
Strong acids have pKa value < −2.
When the pH of solution is at the value of pKa for a dissolved acid, that acid will be 50% dissociated.
Sulfuric acid, H2SO4 --> HSO4-, pKa -10
Hydroiodic acid, HI, HI (g) + H2O (l) --> H3O+(aq) + I-(aq), pKa -9
Hydrobromic acid, HBr
HBr (g) + H2O (l) --> H3O+(aq) + Br-(aq), pKa -8
Perchloric acid, HClO4
HClO4 + H2O --> H3O++ ClO4-, pKa -10
Hydrochloric acid HCl, HCl (g) + H2O (l) --> H3O+(aq) + Cl-(aq), pKa -7
Hydronium ion, H3O+
H2O + H2O < --> H3O++ OH-, pKa -1.74
Nitric acid HNO3
HNO3 + H2O --> H3O++ NO3-, pKa - 1.3
Chloric acid, HClO3, pKa -1.0
Weak acid has pKa value −2 to 12 in water.
Acetic acid, CH3COOH, pKa 4.75
12.3.0.4 pH
Water can transfer a proton from one molecule to another, autionization.
2H2O <--> H3O++ OH-and H2O < --> H++ OH-
The product of hydrogen ion concentration, [H+] and hydroxide ion concentration, [OH-] = the constant, Kw
Kw = [H+] × [OH-] = 1.00 × 10-14
So [H+] = 10-7and [OH-] = 10-7
The hydrogen ion concentration is very small in pure water, so the concentration is describes in terms of its negative log.
pH is the negative log of the hydrogen ion concentration, pH = -log[H+], so hydrogen ion concentration, [H+] = 10-pH.
So acidic solutions have a high [H+] and low pH values.
Basic solutions have low [H+] and high pH values.
A solution that is neither acidic nor basic, a neutral solution, has [H+] = [OH-], so pH = 7.
A more acid solution has pH approaching 1.
A more basic solution has pH approaching 14.
12.3.0.5 Ionization reaction of carbonic acid
H2O (l) --> H+(aq) + OH-(aq)
2H+(aq) + CO32-(aq) < --> H2CO3 (aq) carbonic acid
CO2 + H2O <--> H3O++HCO3-, K1 = 4.4 × 10-7
HCO3-+ H2O <--> H3O++ CO32-, Ka = 4.7 × 10-11
12.3.1 Taste of acids
BE CAREFUL! NEVER TASTE ACIDS IN THE LABORATORY!
Citric acid C6H8O7
Acetic acid Ethanoic acid, CH3COOH
Do NOT taste these acids in the laboratory!
Each acid has a sour taste that is a characteristic of acids.
Lemon juice contains the white crystalline citric acid.
Vinegar contains ethanoic acid, acetic acid, CH3COOH.
Moisten your finger with a very dilute solution of hydrochloric acid.
Rub your fingers together and then lick them.
Repeat the procedure with very dilute solutions of acetic acid and citric acid.
Do not taste any other acids, because they may damage living tissues.
12.3.2 Dilute acids with metals, hydrochloric acid
Reactions of acids with metals are exothermic.
The higher the metal is in the reactivity series the greater the heat liberated.
Dilute hydrochloric acid with zinc
Zn (s) + 2HCl (l) --> H2 (g) + ZnCl2 (aq)
The order of activity of metals with acids is similar to the order of activity with water.
Evolution of hydrogen occurs.
Table 12.3.2

Metal 2M Hydrochloric acid 2M Sulfuric acid
Magnesium very rapid rapid
Aluminium slight none
Zinc moderate Slight
Iron very slight very slight
Tin none none
Lead none none
Copper none none

1. Use different cleaned metals, e.g. calcium pieces, iron nail, lead sinker, magnesium ribbon, copper wire, aluminium sheet and zinc granules.
Rub them with emery paper to make surfaces clean of oxides.
Put each metal into a separate test-tube.
Add 10 mL of 2 M hydrochloric acid to test-tubes.
Observe the properties of any gas liberated and name it.
Test it with moist pieces of red and of blue litmus paper, with a drop of limewater hanging from a glass rod and with a lighted splint.
Compare the rate at which hydrogen gas evolves by noting the rate and size of the hydrogen gas bubbles from the reaction.
Describe the rate of reaction:
Nil | very slow | slow | moderately fast | very fast | and whether energy in the form of heat is 1. produced (exothermic) or 2. absorbed (endothermic).
List the acids in order of their activity towards metals.
State whether the same gas was liberated during each reaction and whether a salt may be isolated when the acids react with a metal.
2. Make up a reactivity series by listing the elements in approximate order of their activity with respect to acids, from the most active to the least active.
Compare the results with the table of the reactivity series of some metals.
The order of activity of the metals used, from the most active to the least active is as follows:
Magnesium | aluminium | zinc | iron | lead and copper - no noticeable reactions.
When reaction did occur, the gas liberated was hydrogen gas.
The reactions of these acids with metals are exothermic.
The order of activity of the acids is that dilute hydrochloric and dilute sulfuric acids are about equal in activity, but that they are more reactive than acetic acid.
The order of activity of the metals with respect to acids is similar to that with respect to water.
Magnesium ribbon forms most rapid bubbles of hydrogen gas then zinc then iron.
Tin forms few bubbles of hydrogen gas.
Copper forms no bubbles of hydrogen gas.
Lead forms some lead chloride precipitate on the surface of the lead.
Aluminium develops a layer of aluminium oxide that obstructs further chemical reactions.
3. Note the properties of any gas that forms.
Test the gas with moist litmus paper a lighted splint and a hanging drop of limewater on a glass rod.
4. Feel the test-tube to note whether heat energy is released or absorbed.
The reactions of these acids with metals are exothermic.
5. List the elements in approximate order of their activity with respect to hydrochloric acid from the most active to the least active.
The order of activity is, magnesium, aluminium, zinc, iron, lead (no noticeable reaction), copper (no noticeable reaction).
12.3.2.1 Dilute acids with metals, sulfuric acid, hydrochloric acid, ethanoic acid
Dilute hydrochloric and dilute sulfuric acids are about equal in activity, but that they are more reactive than ethanoic acid (acetic acid).
Note the slower production of hydrogen gas with the weak acetic acid.
The reaction with sulfuric acid forms insoluble sulfates on the surface of calcium and lead that obstructs or stops reactions.
List the acids in order of their activity on metals.
2CH3COOH (aq) + Mg (s) --> Mg(CH3COO)2 (aq) + H2 (g)
ethanoic acid + magnesium --> magnesium ethanoate + hydrogen
12.3.3 Dilute sulfuric acid with steel wool
Add dilute sulfuric acid to steel wool in a test-tube.
Test the gas that forms with a lighted taper.
BE CAREFUL! THE GAS IS HYDROGEN GAS!.
Heat the mixture in a beaker of hot water until all the steel wool has dissolved.
Add more acid when necessary.
Filter the hot solution then leave it to cool.
Crystals form on cooling.
If no crystals form, add alcohol, because the salt is less soluble in it.
Dry the green crystals of iron (II) sulfate-7-water between absorbent paper.
Fe (s) + H2SO4 (aq) --> H2 (g) + FeSO4 (aq)
12.3.3.1 Dilute sulfuric acid with aluminium
Heat dilute sulfuric acid with pieces of aluminium foil in a test-tube.
Some effervescence occurs, but sometimes not enough to test for hydrogen gas with a lighted taper.
After heating for 5 minutes, decant the solution that contains aluminium sulfate into another test-tube and add ammonia solution.
A white jelly-like precipitate of aluminium hydroxide forms.
12.3.3.2 Magnesium with sodium hydrogen sulfate
Add 3 cm of magnesium ribbon to 3 cm of sodium hydrogen sulfate solution in a test-tube.
The metal reacts with the sulfuric acid in the solution.
Describe what you see.
Tests for hydrogen gas.
Remove any magnesium that has not reacted from the solution, pour part of the liquid into an evaporating basin and leave for magnesium sulfate crystals to form.
12.3.3.3 Iron with sodium hydrogen sulfate
Add a finger width of iron filings to a finger width of sodium hydrogen sulfate solution in a test-tube.
Heat the mixture to speed up the reaction.
The metal reacts with the sulfuric acid in the solution.
Describe what you see.
Tests for hydrogen gas.
Leave to stand until all bubbles have ceased to appear.
Pour part of the liquid into an evaporating basin and leave for magnesium sulfate crystals to form.
Test the liquid with universal indicator paper.
(The indicator changes colour to red, orange, or yellow for acids and green or violet for alkalis.).
Pale green is the colour for neutral substances.
Before testing, make the paper this colour by dipping it into neutral tap water for a few moments.
The Universal indicator turns yellow indicating the presence of an acid.
Filter the liquid, pour part of the clear solution into the evaporating basin, leave for pale green crystals of iron sulfate to form FeSO4.7H2O, green vitriol.
A solution of a salt is not necessarily neutral, because some salts, like iron sulfate, form acids when dissolved in water.
12.3.4 Dilute acids with non-metals, carbon, sulfur
Add a piece carbon and sulfur to dilute hydrochloric acid, dilute sulfuric acid and dilute ethanoic acid (acetic acid) in separate test-tubes.
Heat the test-tubes.
No reaction occurs.
Non-metals do not react with dilute acids.
12.3.5 Dilute acids with basic oxides, metal oxides, copper (II) oxide
1. Heated dilute acids react with metal oxides to form a salt and water.
Pour dilute sulfuric acid into a Pyrex test-tube and heat in a beaker of boiling water until the sulfuric acid is nearly boiling.
BE CAREFUL!
Add pieces of copper (II) oxide one by one while stirring until some remains unreacted with the acid.
Filter the undissolved copper oxide from the hot solution.
Leave the filtrate in a watch glass to cool and form crystals.
Blue crystals of copper (II) sulfate-5-water form with water.
Remove the crystals and dry them by pressing between absorbent paper.
H2SO4 (aq) + CuO (s) --> CuSO4 (aq) + H2O (l)
acid + basic oxide --> salt + water
2. Repeat the experiment with dilute nitric acid.
2HNO3 (aq) + CuO (s) --> Cu(NO3)2 (aq)+ H2O (l)
12.3.5.1 Dilute acids with amphoteric oxides
Oxides of Sn, Al, Zn, Pb, and Sb are amphoteric.
Amphoteric oxides react with bases to form a salt + water.
Amphoteric oxides react with acids to form a salt + water.
Add dilute hydrochloric acid to zinc oxide.
2HCl (aq) + ZnO (s) --> ZnCl2 (aq) + H2O (l)
2NaOH (aq) + ZnO (s) --> Na2ZnO2 (aq) + H2O (l)
12.3.5.01 Copper oxide with sodium hydrogen sulfate
Add half a test-tube of sodium hydrogen sulfate solution to copper oxide in a test-tube.
Heat the solution slowly until it turns blue.
Be careful of spurting from the test-tube.
Some copper oxide may remain after the reaction.
Filter the solution obtain the filtrate of copper sulfate solution.
12.3.6 Dilute acids with hydroxides, magnesium hydroxide
Basic hydroxides are insoluble in water and react with acids to form a salt and water.
Many metallic hydroxides react with acids to form a salt and water.
Add magnesium hydroxide to dilute sulfuric acid until the reaction stops.
Filter the mixture.
Test the filtrate with litmus paper.
Evaporate the filtrate to dryness so that crystals form.
Mg(OH)2 (s) + H2SO4 (aq) --> MgSO4 (aq) + H2O (l)
12.3.7 Dilute acids with hydroxides, sodium hydroxide
Acids react with (neutralize) alkalis to form a salt and water.
Pour 5 mL of dilute sodium hydroxide solution into a watch glass.
Test with litmus paper.
Red litmus turns blue.
Add dilute hydrochloric acid drop by drop.
Stir as each drop is added.
Test the mixture with the litmus paper until the litmus paper is neither red nor blue, but between these colours.
Evaporate the solution to dryness by heating the watch glass over a beaker of boiling water.
Crystals of sodium chloride (common salt) form.
12.3.7.1 Dilute acids with sodium hydroxide
Repeat the previous experiment with, dilute sulfuric acid, dilute nitric acid, ethanoic acid (acetic acid).
HCl (aq) + NaOH (aq) --> NaCl (aq) + H2O (l)
hydrochloric acid + sodium hydroxide --> sodium chloride + water
12.3.7.2 Dilute hydrochloric acid with hydroxides
[NH3 (aq) is used, because while "NH4+" ions and "OH-" ions can be detected, "NH4OH" cannot be detected.
Consequently, so ammonia solution is shown as "NH3 (aq) + H2O (l)"].
Repeat the experiment with dilute solutions of, potassium hydroxide, calcium hydroxide, aqueous ammonia solution.
acid + (base) alkali --> salt + water.
HCl (aq) + NaOH (aq) --> NaCl (aq) + H2O (l)
HNO3 (aq) + NaOH (aq) --> NaNO3 (aq) + H2O (l)
HCl (aq) + KOH (aq) --> KCl (aq) + H2O (l)
HCl (aq) + NH3 (aq) + H2O (l) --> NH4Cl (aq) + H2O (l)
12.3.8 Dilute acids with acidic oxides (non-metal oxides)
BE CAREFUL! DO THIS EXPERIMENT IN A FUME CUPBOARD!
Note any reaction for five minutes then evaporate to dryness.
In each case, no reaction occurs.
In each experiment there is no precipitate.
If you evaporate a sample of a remaining solution to dryness in a fume cupboard, no residue remains.
Pass carbon dioxide through hydrochloric acid or ethanoic acid (acetic acid) solution.
Pass sulfur dioxide through hydrochloric acid or ethanoic acid (acetic acid) solution.
12.3.9.0 Dilute acids with common carbonates
Dilute acids react with metal carbonates to form a salt, carbon dioxide and water.
Geologists use this reaction to identify calcium carbonate in rock.
Drops of hydrochloric acid cause bubbles to form.
1. Add 5 mL vinegar or dilute hydrochloric acid or dilute sulfuric or dilute nitric acid to pea size amounts of finely divided common carbonates,
e.g. sodium hydrogen carbonate, sodium carbonate, calcium carbonate, magnesium carbonate, limestone, lime, oyster shells, egg shell, snail shell, coral.
Continue to add the solid until no further reaction occurs.
Filter and evaporate the filtrate to dryness.
Note any visible changes.
Test any gas liberated by inserting in the mouth of the test-tube.
* damp pieces of red and of blue litmus paper then,
* a drop of limewater hanging on the tip of a glass rod,
and finally, a burning splinter.
In each case the gas is carbon dioxide.
12.3.9.1 Dilute hydrochloric acid with calcium carbonate
See diagram 9.154, Limewater test for carbon dioxide in the breath
1. Put calcium carbonate in a test-tube.
Add 2 mL 1.0 M hydrochloric acid.
Tilt the test-tube so that its mouth is touching a second test-tube containing 5 mL of limewater.
The surface of the limewater turns milky.
Shake the test-tube containing the limewater.
The milky colour on the surface disappears.
CaCO3 (s) + 2HCl (aq) --> CO2 (g) + CaCl2 (aq) + H2O (l)
calcium carbonate + acid --> carbon dioxide + salt + water
2. Put 5 g of marble chips (calcium carbonate) and the same quantity of dilute hydrochloric acid in a test-tube fitted with a one-hole stopper and delivery tube.
With the end of the delivery tube dipping into a second test-tube of limewater, add water to the first test-tube and quickly replace the stopper.
The limewater turns milky.
The acid reacts with calcium carbonate to form a salt, carbon dioxide, and water.
hydrochloric acid + calcium carbonate --> calcium chloride + carbon dioxide + water.
12.3.9.2 Dilute hydrochloric acid with sodium carbonate
1. Put sodium carbonate in a test-tube and add drops of dilute hydrochloric acid.
Test any gases formed from the reaction with moist litmus paper, a lighted splint, and a drop of limewater on a glass rod.
The reaction forms carbon dioxide.
Add more carbonate until no more reaction occurs.
Filter and evaporate the filtrate to dryness.
Repeat the experiment with dilute nitric acid.
Repeat the experiment with magnesium carbonate.
Na2CO3 (s) + 2HCl (aq) --> 2NaCl (aq) + H2O (l) + CO2 (g)
Na2CO3 (s) + 2HNO3 (aq) --> 2NaNO3 (aq) + H2O (l) + CO2 (g)
2. Sodium carbonate with hydrochloric acid
Stage 1. Na2CO3 + HCl - --> NaHCO3 + NaCl
Stage 2. NaHCO3 + HCl - --> NaCl + H2O + CO2
Overall equation, Na2CO3 + 2HCl - --> 2NaCl + H2O + CO2
Net ionic equation, CO32-+ 2H+ --> H2O + CO2
3. Shake different solid acids in separate test-tubes half filled with water.
Divide the solutions in the test-tubes into three different test-tubes,
Test-tube A, Add small pieces of red and of blue litmus paper.
Test-tube B, Add three drops of methyl orange solution.
Test-tube C, Add three drops of phenolphthalein solution.
Observe any changes in the solutions.
Add solid sodium carbonate to each acid solution.
Observe any changes in the solutions.
Pass some gas given off into a test-tube containing limewater.
Shake the test-tube for thorough mixing.
Note how milky the solution is, because carbon dioxide was produced when the acids reacted with sodium carbonate.
12.3.9.3 Dilute tartaric acid with sodium carbonate
Put 5 g of sodium carbonate and the same quantity of tartaric acid in a test-tube fitted with a one-hole stopper and delivery tube.
With the end of the delivery tube dipping into a second test-tube of limewater add water to the first test-tube and quickly replace the stopper.
The limewater turns milky.
The acid reacts with sodium carbonate to form a salt, carbon dioxide, and water.
tartaric acid + sodium carbonate --> sodium tartrate + carbon dioxide + water
12.3.9.4 Dilute tartaric acid with egg shell, soil, wood ash
Many common substances, such as mortar, egg shell, most soils, contain calcium carbonate and wood ashes contain potassium carbonate.
Observe the action of tartaric acid on these substances in a test-tube.
Tests for carbon dioxide by holding a drop of limewater, at the end of a glass tube, in the mouth of the test-tube.
12.3.9.6 Dilute sulfuric acid with calcium carbonate
Put 5 g of marble chips, (calcium carbonate), and the same quantity of dilute sulfuric acid in a test-tube fitted with a one-hole stopper and delivery tube.
With the end of the delivery tube dipping into a second test-tube of limewater add water to the first test-tube and quickly replace the stopper.
The limewater turns milky.
The acid reacts with calcium carbonate to form a salt, carbon dioxide, and water.
The reaction of sulfuric acid with calcium carbonate proceeds only for a few moments.
The salt formed, calcium sulfate, is only slightly soluble and deposits on the carbonate, preventing this compound from reacting with the acid.
So the reaction with hydrochloric acid above is much better.
sulfuric acid + calcium carbonate --> calcium sulfate + carbon dioxide + water
12.3.10.0 Dilute acids with sodium hydrogen carbonate
3.3.1 Soda-acid fire extinguisher
The only stable hydrogen carbonates are KHCO3 and NaHCO3.
Sodium hydrogen carbonate, bicarbonate of soda, is used in baking soda, baking powder, self raising flour, effervescent fruit salts,
e.g. Alka-Seltzer, and soda acid fire extinguishers. and used to treat acid burns.
Some people swallow sodium hydrogen carbonate to counteract excess acid in the stomach.
However, but it is better to use magnesium oxide or magnesium hydroxide that does not react with acids to produce carbon dioxide.
1. Add sodium hydrogen carbonate, or other hydrogen carbonates, to acids to form carbon dioxide, water and a salt.
NaHCO3 + HCl --> CO2 + H2O + NaCl
hydrogen carbonate + acid --> carbon dioxide + water + salt
2. Mix vinegar with bicarbonate of soda in a glass jar.
Drop naphthalene mothballs into the solution.
The carbon dioxide formed by the vinegar with the sodium hydrogen carbonate forms carbon dioxide bubbles on the mothballs at the bottom of the jars.
The mothballs rise to the surface, lose the bubbles and sink again.
NaHCO3 + CH3COOH --> CH3COONa + H2O + CO2 (g)
12.3.10.1 Dilute acids with calcium hydrogen carbonate
Put powdered calcium carbonate into a test-tube containing about 10 mL of water.
Bubble carbon dioxide through the suspension until no further change takes place.
Soluble calcium hydrogen carbonate forms.
Boil the mixture for 10 minutes.
Add acids to form carbon dioxide, water and a salt.
12.3.11.0 Dilute nitric acid with copper
Very dilute nitric acid may react with very active metals, e.g. magnesium to form hydrogen gas.
When nitric acid reacts with most metals, it oxidizes the hydrogen to water.
Add drops of dilute nitric acid to copper.
Nitrogen monoxide forms, which immediately reacts with oxygen gas in the air to form nitrogen dioxide.
3Cu (s) + 8HNO3 (aq) --> 3Cu(NO3)2 (aq) + 4H2O (l) + 2NO (g)
2NO (g) + O2 (g) --> 2NO2 (g)
12.3.11.1 Nitric acid with metals
Add slowly small pieces of copper, magnesium and zinc to small amounts of dilute nitric acid in separate test-tubes.
If no change is taking place, gently heat the mixture.
Repeat the procedure, 1. with concentrated nitric acid, 2. with concentrated sulfuric acid, and 3. with concentrated hydrochloric acid.
Reactions of metals with nitric acid and conc. sulfuric acid are different from reactions of metals with hydrochloric acid, dilute sulfuric acid and dilute acetic acid.
Copper does not react with dilute acids or with concentrated hydrochloric acid.
However, it does react with both dilute and concentrated nitric acids and with hot concentrated sulfuric acid, but does not produce hydrogen gas in reaction with them.
Residual mixtures contain solutions of salts, but writing equations is difficult, because more than one reaction can occur between Cu, Mg, Zn and nitric acid.
For example, when zinc reacts with nitric acid the reaction may produce nitrogen dioxide, nitric oxide, nitrous oxide, zinc nitrate and ammonium nitrate.
12.3.12 Concentrated acids with metals, nitric acid with copper
Nitric acid reacts with metals above platinum in the reactivity series, but does not form hydrogen gas.
BE CAREFUL! DO THIS EXPERIMENT IN A FUME CUPBOARD.
Pour drops of concentrated nitric acid on pieces of copper in a test-tube.
Put a stopper on the test-tube immediately, because brown nitrogen dioxide gas forms.
The nitric acid acts as an oxidizing agent and is reduced to nitrogen dioxide and water.
The reaction is exothermic.
Cu (s) + 4HNO3 (aq) --> Cu(NO3)2 (aq) + 2H2O (l) + 2NO2 (g)
12.3.13 Sulfuric acid with copper
Concentrated acids should be handled only by experienced science teachers.
Concentrated sulfuric acid reacts with metals above platinum in the reactivity series, but does not form hydrogen gas.
BE CAREFUL! DO THIS EXPERIMENT IN A FUME CUPBOARD.
Add hot concentrated sulfuric acid to a piece of copper foil.
Brown nitrogen dioxide gas forms.
The sulfuric acid acts as an oxidizing agent.
Cu (s) + 2H2SO4 (aq) --> CuSO4 (aq) + 2H2O (l) + SO2 (g)
12.3.14 Concentrated acids with a non-metals, carbon
DO NOT DEMONSTRATE THIS EXPERIMENT!
Hot sulfuric acid and nitric acid can react as oxidizing agents with carbon.
Carbon is oxidized to carbon dioxide and nitric acid is reduced to nitrogen dioxide and water.
C (s) + 4HNO3 (aq) --> CO2 (g) + 4NO2 (g) + 2H2O (l)
12.3.15 Dilute acids with salts
1. Add small quantities of sodium chloride, sodium nitrate, sodium sodium sulfite and iron sulfide to about 5 mL of dilute hydrochloric acid in separate test-tubes.
Observe what happens when the mixtures are cold and when they are warmed.
2. Repeat the procedure using dilute sulfuric acid and then concentrated sulfuric acid.
3. Dilute acids do not react with chlorides, nitrates, sulfates, or acetates, unless the metal ions in the salt can form an insoluble salt with the ions in the acid.
4. Acids react with sulfites to produce sulfur dioxide, water and a salt.
5. Acids react with sulfides to produce hydrogen sulfide (rotten egg gas) and a salt.
6. Concentrated sulfuric acid reacts with chlorides to produce hydrogen chloride and a sulfate.
7. Concentrated sulfuric acid reacts with nitrates to produce nitric acid and a sulfate.
8. Concentrated sulfuric acid reacts with s to produce acetic acid and a sulfate.
12.3.16 Acid dissociation constant
Acid dissociation constant, acidity constant, acid-ionization constant
1. The acid dissociation constant, Ka, measures the strength of an acid in solution.
2. An acid, HA, dissociates into A-, conjugate base, and H+, hydrogen ion (proton).
The equilibrium equation when concentrations do not change is, HA < --> A-+ H+.
3. Dissociation refers to the break up of a molecule into smaller molecules, atoms or ions.
In a buffer solution of the salt of a weak acid with a weak acid, the dissociation of the weak acid is negligible, but a salt may be dissociated completely into ions.
4. The dissociation constant, Ka is the equilibrium constant of a reversible dissociation including the ionization reactions of acids and bases in water.
The dissociation constant Ka = [A-] [ H+] / [HA] in mol / litre.
5. However, dissociation is usually expressed as a logarithmic constant, pKa, where pKa = -log10 (1/Ka).
It is the quotient of the equilibrium concentrations, in mol/L for ionization reactions at 25oC.
For pKa, the larger the value the weaker the acid, so strong acids have pKa < 2, and weak acids have pKa >2, < 12.
6. Confusion happens, because both Ka and pKa are sometimes both called "acid dissociation constant"!