School Science Lessons
Chemistry
2025-08-31
Chemistry, Aa to Ac
Contents
AAS Atomic Absorption Spectroscopy
Abbreviations Chemistry
Abbreviations English language
Abrin
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
Acepromazine
Acerosin
4.9.1 Acephate
Acesulfame
Acetal
Acetaldehyde, (Experiments)
Acetates, Ethanoates, (Experiments)
Acetyl group, −COCH3, −C(=O)−CH3, Ac, ethanoyl
Acetylharpagide
Acetamide, (Experiments)
Acetaminophen, Paracetamol, (Experiment)
Acetamiprid, Neonicotinoid insecticide
Acetic acid, Ethanoic acid, (Experiments)
Acetic alcohol, Prepare, (Experiment)
Acetic anhydride, Prepare
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), (Experiments)
Acetylpyrrolidine
Acetylpyrroline
Acetylsalicyclic acid, Aspirin, (Experiments)
Achillin
Acid-base indicators, (Experiments)
Acid acid-, acids, acidic, acidify, (Experiments)
Acid anhydrides
Acid fuchsin, Prepare
Acid rain
Acidity, (Experiments)
Acolongifloroside K
Aconine
Aconitine
Acridine
Acriflavine
Acrilan (trade name)
Acroleic acid
Acrolein
Acronidine
Acryl polymer (Experiments)
Acrylamide
Acrylates
Acrylic acid, "acrylics"
Acrylic glass Polymethyl methacrylate, (Experiments)
Acrylonitrile (Experiments)
Actinides actinoids
Actinidine
Actinium, Ac
Actinolite, (Geology)
Activated carbon activated charcoal
Active constituent (Pesticides label)
Activity series of metals as reducing agents
Acute toxicity
Acyclic hydrocarbons
Acyl halide
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.
Absinthin
Absinthin, C30H40O6, a sesquiterpene lactone, a triterpenoid, anti-inflammatory agent, nervousness, convulsions
It occurs in Wormwood (Artemisia absinthium).
Artemisia absinthium, anthelmintic, flavouring Vermouth, is a bitter-tasting constituent of Absinthe.
Abietic acid
Abietic acid, C20H30O2, sylvic acid, abietate, diterpenoid, colophony rosin, Greek pitch, a monocarboxylic acid, irritant
It is a yellow resinous powder, and it is used on violin bows and ballet shoes.
It is a main component of Gums rosin.
It is used to make varnishes, soaps, plastics), most abundant compound in rosin, in Pinus.
Acepromazine
Acepromazine, C19H22N2OS, a phenothiazine, psychotropic drugs, used as a sedative and antiemetic
Alleged overuse of Acepromazine on race horses in Australia.
Acerosin
Acerosin, C18H16O8, is a trimethoxyflavone metabolite.
It occurs in Scoparia, Iva, 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
Food code E962, salt of aspartame-acesulfame, artificial sweetener, emulsifier, stabilizer, thickener and gelling agent, Health risk
19.6.3 Cola, Diet or Light contents
Acesulfame potassium, C4H4KNO4S, or Ace-K, is a zero-calorie sweetener in foods and drinks.
It occurs in combination with the sweetener disaccharide derivative Scralose, C12H19Cl3O8, in Splenda.
or in combination with the dipeptide Aspartame, C14H18N2O5, in Equal or Coke Zero.
Acesulfame K is also sold under the brand names "Sunett" and "Sweet One".
The fact that the crystal powder has a bitter aftertaste is the main reason for mixing it in sweeteners.
The mixture of sweeteners is used to create a sugar taste.
Acetaldehyde
Acetaldehyde C2H4O, CH3CHO, ethanal, colourless liquid, BP 21°C, choking vapour irritates eyes, tobacco smoke carcinogen.
16.3.2.7 Ethanal with potassium dichromate, Prepare
16.3.2.6 Ethanal with potassium manganate (VII), Prepare
Acetamide
Acetamide, CH3CONH2, C2H5NO, ethanamide, acetic acid amide, colourless crystals, mouse odour, low toxicity, 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
16.1.5.6 Amides
24.7.3 Heat energy changes solid to liquid
24.7.5 Latent heat of fusion of ice to water
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 little in aqueous solution.
However, their salts, e.g. potassium acetate CH3COOK are completely dissociated into ions.
Acetic anhydride (CH3CO)2O
3.5.7 Celluloid
3.5.8 Cellulose acetate, Cellulose triacetate
Experiments
12.3.9 Acids with salts
16.4.2 Ethyl acetate, Prepare
17.3.5 Ethyl acetate with sodium hydroxide, autocatalyctic hydrolysis
Acanthosides
Acanthoside B, Eleutheroside e1, C28H36O13, syringaresinol beta-D-glucoside
It occurs in (Eucommia ulmoides) bark, and in (Acanthopanax sessiliflorus) roots
Acanthoside D, Syringaresinol-di-O-glucoside, Liriodendrin, C34H46O18, beta-D-glucoside, antioxidant, anti-inflammatory
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
You can 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 in (Apium graveolense).
16.1.9 Ethyl acetoactonate
16.3.3 Keto acids
19.5.1Tests for ketones
Acetone
Acetone, CH3COCH3, 2-propanone, a dimethyl ketone, is highly flammable, 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, (not Australia), e.g. "Cutex", nail paint remover and thinner
It may be sold as "pure acetone".
Junior secondary students should use acetone only as a cold solvent, and they should not heat acetone.
2.3.7 Cleaning agents, solvents
3.1.2 Boiling point of inflammable liquids
12.19.9.7 Bromination of acetone
15.4.16 Potassium dichromate as an oxidizing agent, (See: 5.)
Experiments
10.12.0 Separate by solvent extraction of oil from peanuts
17.3.7 Oxidation of acetone vapour, copper catalyst
Acetonitrile
See diagram Acetonitrile
Acetonitrile, CH3CN, (acetonitrilo), cyanomethane, methyl cyanide, flammable, colourless liquid, sweet ether-like odour
It is the simplest organic nitrile and it is 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, non-steroidal anti-inflammatory, anti-asthmaticg, non-narcotic analgesic.
It occurs in (Justicia adhatoda), (Polyporus umbellatus), and in (Saccharomyces cerevisiae).
It occurs in (Nicotiana tabacum) root cultures, exuded from roots, to cause infection by (Agrobacterium tumefaciens).
Acetoxychavicol acetate
Acetoxychavicol acetate, C13H14O4, is a galangal acetate, an acetate ester, a phenylpropanoid, and an antineoplastic agent.
It occurs in Sweet flag, (Acorus calamus), Acoraceae, and in Snap ginger, (Alpinia calcarata), Zingiberaceae
Acetoxyeugenol acetate
Acetoxyeugenol acetate, C14H16O5, is a phenylpropanoid, a monomethoxybenzene.
It occurs in Greater galangal, (Alpinia galanga), Zingiberaceae, and in Snap ginger, (Alpinia calcarata), Zingiberaceae
Acetylbrowniine
Acetylbrowniine, C27H43NO8, 14-O-Acetylbrowniine, is an acetate ester obtained by acetylation of browniine, C25H41NO7.
Acetyl chloride
Acetyl chloride, C2H3ClO, CH3COCl, C2ClH3O, ethanoyl chloride, acyl chloride, acetic chloride, has low flash point.
It is toxic colourless, fuming liquid, pungent odour, vapour heavier than air, irritates eyes and mucous membranes, corrodes metals.
Acetylcholine
Acetylcholine C7H16NO2+, neurotransmitter, stimulates muscle, acetyl ester of choline, is a 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
Acetylharpagide
Acetylharpagide, C17H26O11, 8-O-Acetylharpagide, iridoid glucoside, ecdysteroid
Chinese medicine, anti-inflammatory, vasoconstrictor, antibacterial, antiviral, acts on smooth. muscle, inhibits, Epstein-Barr virus (EBV).
It occurs in Ajuga decumbens, and in Ajuga reptans
Acetylpyrrolidine
Acetylpyrrolidine, C6H11NO, 2-Acetylpyrrolidine
Substituted pyrrolidine, CH3COC5H4N, occurs in malt, popcorn, and beer
Acetylpyrroline
Acetylpyrroline, C6H9NO, 2-Acetyl-1-pyrroline (2AP), occurs in jasmati and basmati rice, wheat bread crust, sweet corn.
It is the white bread smell in cereals, and hot popcorn.
It occurs in screwpine, Pandanus.
Achillin
Achillin, C15H18O3, santolin, sesquiterpene lactone, a guaianolide, plant growth inhibitor
It occurs in Achillea, and in Artemisia.
Acids
7.4.1 Acids
Acid-base indicators
19.1.1 Acid-base indicators in the home
12.11.4.1 Acid-base neutralization
12.2.1 Acid-base reactions
16.1.5.7 Acid anhydrides
12.3.0.6 Acid dissociation constants
12.3.0.7 Acid dissociation constant at logarithmic scale, pKa
12.3.15 Acid dissociation constant at logarithmic scale, pKa
1.0.0 Acid fuchsin indicator, Andrade's
Acid rain
12.3.0 Acids, Chemical reactions
19.1.5 Acids in foods, Food acids
1.1 Acids, List of mineral acids
1.2 Acids, List of organic acids
Acids with other substances
Acidic oxides (Experiments)
Acidity
19.1.2 Acidulated water, Cooking
12.3.0.1Amphoteric substances
3.9.0 Carbonic acid, soda water
12.3.5 Concentrated acids, with a non-metal, carbon
12.3.10 Concentrated acids, with metals, H2SO4 + Cu
12.3.12 Concentrated acids with metals, nitric acid with copper
12.3.14 Concentrated acids with a non-metals, carbon
12.4.0 Dilute acids with
12.3.0.5 Ionization reaction of carbonic acid
12.3.11.1 Nitric acid with metals
12.3.0.4 pH
12.3.0.2 Polyprotic acids
Prepare acids
12.3.1 Properties of acids
12.16.5 Reactions of sulfuric acid
19.1.17 Solid acids, solubility
12.3.0.3 Strong acids and weak acids
12.11.2 Tests for acid radicals in solution
12.3.17 Taste of acids, solid acids in the home
12.3.1 Taste of acids
12.11.2 Tests for acid radicals in solution
Titration
Acidity
Acidity, definition, [degree of being an acid]
18.1.0.1 Acidity and alkalinity
12.11.4.2 Acidity of vinegar and wine
19.1.1 Acidity regulators, food additives
16.1.5 Acidity test, (milk testing)
6.1.0 Soil acidity
Prepare acids
5.6.4 Prepare acid-base indicators
3.1 Prepare acid alcohol solution
11.0 Prepare acids and bases, dilution instruction
5.4.7 Prepare dilute acids
3.4.10 Prepare dilute acids and bases, (Safety)
Boric acid, Boracic acid, H3BO3
12.3.16, Hydroiodic acid, a strong acid
Hydrochloric acid, HCl
12.19.7.0, Hydrofluoric acid, HF
Nitric acid, HNO3
Nitrous acid, HNO2
Phosphoric acid, H3PO4
Acid rain
12.8.11 Acid rain and nitrogen oxides, NOx
12.6.0.1 Acid rain, SOx, from burning S or S compounds
18.6.0 Air pollution
12.19.5.0 CFCs, "Freons"
Acidic oxides
An acidic oxide is oxide of a nonmetal, e.g. carbon dioxide, or a metal in high oxidation state, e.g. 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)
12.13.01, Acidic oxides
12.13.6, Carbon dioxide, acidic oxides, (non-metal oxides)
12.13.7, Carbon dioxide, with barium hydroxide solution
12.13.8, Carbon dioxide, with sodium hydroxide solution
12.13.0, Reactions of oxides
Acids with other substances
12.3.4 Acids with aluminiums
12.1.18 Acids with baking soda
12.1.25 Acids with sodium carbonate
12.1.40 Acids with sodium thiosulfate
12.14.18 Acids with zinc
12.3.12 Concentrated acids with metals, nitric acid with copper
12.3.14 Concentrated acids with a non-metals, carbon
12.4.0 Dilute acids with
Acridine
Acridine, C13H9N, toxic if ingested and skin contact, give First aid if ingested: Give water, and induce vomiting
Acridine orange, C17H19N3, an aminoacridine, hydrochloride salt 'acridine orange', is used to stain cell nuclei, e.g. DNA.
See diagram Acridine, (9-Azaanthracene), (2,3-Benzoquinoline)
Acriflavine
Acriflavine, C14H14ClN3, orange-brown, dye and antiseptic
It shows green fluorescence when diluted in water.
Acroleic acid
Acroleic acid, CH2CHCO2H, C3H4O2, acrylic acid, propenoic acid, prop-2-enoic acid, Toxic
It is 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, (C3H3NaO2)n, waterlock, is sold as toy product "Super Expanding Creatures".
3.1.22 Sodium polyacrylate gels, ghost crystals, Prepare
Acrolein
Acrolein, CH2CHCHO, CH2=CHCHO, C3H4O, acrylaldehyde, 2-Propenal, ethylene aldehyde, acrylic aldehyde
It is the simplest unsaturated aldehyde, colourless or yellow liquid, and a toxic chemical.
It has a horrible odour like the smell of burnt fat when glycerol breaks down into acrolein.
Acrolein test for presence of fats: Heat sample with potassium bisulfate --> acrolein released
Acrolein, Solution < 0.1%, Not hazardous, clear, yellowish liquid, sweet, pungent burnt fat smell, highly flammable
It polymerizes in the presence of light or alkali, or strong acids, and is unstable.
It occurs in cigarette smoke and vehicle exhaust, aquatic herbicide, kill algae and waterweeds, and it is used as a pesticide.
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.
Acrylonitrile
Acrylonitrile, CH2=CH-CN, flammable, low flashpoint, below 32 oC, 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
16.7.6 Nitriles
4.3.1 Acrylonitrile-butadiene-styrene, burning test for synthetic fibres
3.4.2 Chewing gum (Tg)
Actinium Ac
Actinium Table of Elements
Actinium RSC
Actinium, Ac, (Greek actinray), refers to light causing chemical change, radioactive, no commercial use.
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.
19.1.17 Solid acids, solubility
19.1.11 pH of solid acids
19.1.16 Solid acids, add sodium carbonate
19.1.17 Solid acids, solubility
Citric acid
Tartaric acid
Boric acid
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.
Represent the hydrogen ion, a proton, in different ways to show how it is related to the water molecules in the solution.
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.
Use 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.
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
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
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.)
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.
It does not refer to 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.
12.3.0.6 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
However, 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 25 oC.
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"!
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.
12.3.0.7 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!
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.
Experiment
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.
Citric acid C6H8O7
9.1.6, Acetic acid, ethanoic acid, CH3COOH
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 HCl, dilute sulfuric acid and dilute acetic acid.
Copper does not react with dilute acids or with concentrated hydrochloric acid.
Copper does react with dilute and concentrated nitric acids and with hot concentrated sulfuric acid.
However, it does not produce hydrogen gas in reaction with them.
Residual mixtures contain solutions of salts.
However, writing equations is difficult, because more than one reaction can occur between Cu, Mg, Zn and nitric acid.
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)
12.3.14 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)
12.3.16 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
However, 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 25 oC.
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"!