School Science Lessons
Chemistry
2025-12-04a

Chemistry Experiments, Q, R

Chemistry, Q, R
Q
R

Chemistry, Q
Contents
Quantity of chemical in experiments
Quark
Quartz
Quartzite
Quassin
Quercetin
Quicklime
Quicksand
Quicksilver
Quinacrine
Quinaldine red indicator
Quinidine
Quinine
Quinol
Quinoline
Quinoline alkaloids
Quinolizidine
Quinolizidine alkaloids
Quinones
Quisqualic acid

Chemistry, R
Contents
Racemic acid, Tartaric acid
Radical
Radioactive element
Radium
Radon
Raffinose
Rain smell, Geosmin
Rainbow reactions, Butyl chloride
Rancidity of fats
Raoult's law
Rapanone
Raphanin
Raphides
Rare earth elements, Lanthanides
Rare gases, Noble gases
Raspberry ketone
Rates of reactions
Ratio and proportion
Rayon
Razor blades and knives
RDX explosive, Nitrosamines
Reactions, Chemical reactions
Reactions of
Reagents, Prepare acids and bases
Reagents, Prepare chemicals
Reagents, solutions in water
Realgar, As4S4
Rebaudioside
Recycle chemicals
Red cabbage indicator
Red lead, Lead (II/IV) oxide
Red phosphorus, P
Red phosphorus, safety matches
Redox
Reduce
Reductants
Reduction reactions
Refrigerator
Regelation
Relative atomic mass, Magnesium
Re-lighting candles
Renewable energy
Rennet
Reproductive toxicity, chemicals
Resazurin indicator
Rescinnamine
Reserpine
Residuals, Bitmen
Resins, Rosins
Resorcinol
Restore bronze coins
Respiration of soaked peas
Resuscitation
Resveratrol
Retinol, Vitamin A
Retamine
Reticuline
Retort stand clamp
Retronecine
Reverse osmosis
Rhamnazin
Rhamnetin
Rhamnose
Rhaponticin
Rhein, rhubarb yellow
Rhenium
Rhodamine
Rhodiolin
Rhodionin
Rhodium
Rhodochrosite
Rhododendrol
Rhodonite
Rhodopin
Rhoeadine
Rhombifoline
Rhodoxanthin
Rhyolite
Riboflavin
Ribose
Ribulose
Rice grain slope
Ricin
Ricinine
Ricinoleic acid
Riddelline
Ridentin
Rifampin
Ringer solution
Risk assessment
Rituximab
RNA
Roasting meat
Rochelle salt
Rock candy crystals
Rock crystal
Rock salt
Rocks
Rodenticides
RODP, Ozone depletion
Roentgenium
Rohypnol
Rosarin
Rose bengal
Rose oxide
Rose petal indicator
Rose quartz
Rosmarinic acid
Rotenone
Rottlerin
Rotundine
RU-486, Mifepristone
Rubeanic acid, copper test
Rubber, Latex
Rubbing alcohol
Rubidium
RuBisCo
Rubixanthin
Rubrofusarin
Ruby, Corundum
Rusting
Rutaecarpine
Ruthenium
Rutherfordium
Rutile
Rutin

Quantity of chemical to be used in school science experiments
Disposal of waste chemicals
1. In this document, "dilute solution" refers to a 2 M solution, or a 10% solution, unless otherwise specified.
2. In this document, "concentrated acid", or any other substance, refers to the concentration supplied by chemical suppliers, e.g. concentrated hydrochloric acid is 36% w / w, unless otherwise specified.
3. For all experiments, unless otherwise instructed, use either:
3.1 a 5 mL of solution, or
3.2 a test-tube filled to the depth of a finger width, or
3.3 the powder on a little finger nail, or
3.4 a piece of solid chemical the size of half a dried pea, or
3.5 no more than one third of a test-tube of any solution.
4. Do not make gas jars full of gas for demonstration purposes.
Use test-tubes with stoppers to collect gases.

Quartz
Silica, SiO2
Quartz: 35.14.0
Construct molecular models (quartz): 11.2.3
Silicon: 12.10.0
Voltage from mechanical stress to crystals, piezoelectricity: 32.1.2.1

Quassin
Quassin, C22H28O6, nigakilactone D, a quassinoid febrifuge, vermicide, bitter tonic
It occurs in Surinam Quassia wood, (Quassia amara).

Quercetin
Quercetin, C15H10O7, [(C6-(C3-(C6], flavonol glycoside, a pentahydroxyflavone, polyphenolic flavonoid, the most active of the flavonoids.
It is a yellow powder, antioxidant in many plants, a phytoestrogen, are used for vegetables in a good diet and food additive.
Many medicinal plants have high quercetin content, anti-inflammatory activity. by inhibiting release of histamine.
Quercetin, antioxidant activity, anticancer, inhibits fatty acid synthase, phytochemical
It causes the colouring found in the skins of apples and red onions.
Quercetin may protect against heart disease and cancer, prevents damage to LDL cholesterol, antioxidant, natural anti-histamine.
It is anti-inflammatory, anti-cancer, but unproved addition to dietary supplements.
It occurs in berries, red grapes, citrus fruit, tomato, and in broccoli.
Do not take quercetin if taking prescribed medicines, are pregnant or breast feeding or have liver disease.

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.
It 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.

Quinidine
Quinidine, (C20H24N2O2), Quinoline Alkaloid
Quinidine, Chinidin, Pitayine, Cin-quin, optical isomer of quinine, antimalarial, anti-arrhythmic in the heart, dampens the excitability of cardiac and skeletal muscles, decreases conduction velocity of nerve impulses
It occurs in Chinchona tree bark.
See diagram: Quinidine.

Quinine
Quinine, (C20H24N2O2), Quinoline Alkaloid
Quinine, Chinin, Chinine, Qualaquin, irritant, alkaloid from cinchona tree bark, antimalarial drug, active ingredient, mild antipyretic
It is an aanalgesic, so it is used in common cold preparations, used to treat idiopathic leg cramps.
Nowadays, it is used as a bitter and flavouring agent in Schweppes Indian Tonic Water.
It occurs in cinchona tree extracts.
See: Quinine.
See diagram: Quinine.

Quinoline
Quinoline, (C9H7N), Quinoline Alkaloid
Quinoline, heterocyclic aromatic organic compound, colourless hygroscopic liquid, strong odour, if exposed to light yellow then brown
It is slightly soluble in cold water, and is used as a flavouring ingredient.
It occurs in Mentha, cocoa, black tea, and in scotch whisky.
See diagram: Quinoline.

Quinoline yellow, (C18H11NO2), mixture of dyes based on quinoline, quinophthalone, solvent yellow, erio chinoline yellow 4G
E104, azo dye is based on quinoline, bright yellow colour, possible health risk is dermatitis, used in lipsticks.

Radium, Ra
Radium, Table of the Elements
Radium, RSC
Radium (Latin radius, spoke), alkaline earth metal
Radium is a radioactive alkaline earth metal, extracted from pitchblende, uraninite, used in cancer therapy, and as a radioactive resource.
Radiation dose from entry of radioactive materials into the body: 7.2.2
Atomic number: 88, Relative atomic mass: 226.025, RD: 5.0, MP: 700 oC, BP:1140 oC
Specific heat capacity: 121 J kg-1 K-1

Radon, Rn
Radon, Table of Elements
Radon, RSC
Radon, Rn (from Ra radioactive decay), in former health spas, Rn-222, Group 18, last noble gas found.
Radon is a non-metal noble colourless water-soluble gas at room temperature and pressure.
Rn2 is formed by decay of radium-226, usually under granite, where it may be a health habit to people living in granite houses.
Radon has few compounds and is used in radiotherapy.
Atomic number: 86, Relative atomic mass: (222), RD: 4.4 (211 K), MP: -71 oC, BP: -61.8 oC
Specific heat capacity = 92 J kg-1 K-1

Rapanone
Rapanone, C19H30O4, is a quinone, benzoquinone, dihydroxy-1,4-benzoquinone, and is antihelmintic.
It occurs in (Rapanea maximowiczii), Aegiceras, and in Oxalis.

Raphanin
Raphanin, C6H9NOS2, sulphoraphene, toxic, antioxidant, antibacterial, and is used in Chinese medicine.
It occurs in seed of Radish, (Raphanus raphanistrum subsp. sativus), Brassicaceae, and in root vegetables.

Rayon
Rayon, viscose, is made from cellulose products and wood.
Rayon polymer: 3.8.14
Rayon, burning test: 4.3.21
Organic builders in washing powders: 12.6.8
Prepare rayon: 3.3.8
Triboelectric series: 31.1.02 See: Negative polarity, 29. Rayon

Reactions of:
Rate of reaction, k: 17.1.11

14.4.0 Reactions of:
Reactions of aluminium:
Reaction of ammonium carbonate with ethanoic acid: 14.4.1
Reaction of ammonium nitrate with water: 14.4.2
Reactions of ammonium salts and potassium salts with water: 14.4.3
Reactions of antimony: 12.2.1
Reactions of arsenic and arsenic compounds: 12.3.3
Reactions of aspirin (rate of reaction): 17.1.13
Reactions of barium compounds: 12.4.1
Reactions of benzene: 16.5.3
Reactions of bismuth compounds: 12.5.1
Reactions of bromides: 12.19.9.6
Reactions of bromine: 12.19.9.1
Reactions of bromine water (bromine solution): 12.19.9.2
Reactions of cadmium sulfate solution: 12.7.1
Reactions of calcium and calcium compounds: 12.4.1
Reactions of carbonates: 12.15.0
Reactions of chloramines in swimming pools: 18.1.5
Reactions of chlorine: 12.19.8
Reactions of chromium compounds, Cr: 12.8.0
Reactions of copper (I) compounds: 12.7.3
Reactions of copper (II) ions: 12.7.2
Reactions of copper (II) oxide, CuO: 12.7.1.0
Reactions of dichromates, potassium dichromate: 12.8.3
Reactions of dilute acids: 12.4.0
Reactions of dilute sulfuric acid as a acid: 12.18.5.4
Reactions of dilute sulfuric acid as a sulfate: 12.16.2.1
Reactions of hydrogen bromide, HBr: 12.19.9.4
Reactions of iodides: 12.19.6.2
Reactions of iron: 14.5.0
Reactions of iron (II) salts and iron (III) salts, Prussian blue: 14.8.1
Reactions of lead (II) salts: 12.9.1
Reactions of lead (IV) salts: 12.9.2
Reactions of lithium with water: 12.9.3
Reactions of magnesium, burning or molten magnesium: 12.10.2
Reactions of magnesium compounds: 12.10.4
Reactions of magnesium oxide: 13.3.6
Reactions of magnesium with carbon dioxide, sparkler experiment: 3.77
Reactions of magnesium with water: 12.10.1
Reactions of manganese (II) salts: 12.8.1
Reactions of mercury compounds: 3.7
Reactions of: Metallic elements
Reactions of metals as reducing agents: 12.14.0
Reactions of metals with air or oxygen gas: 12.14.3
Reactions of metals with concentrated oxidizing acids: 12.14.5
Reactions of metals with dilute acids: 12.14.4
Reactions of metals with steam: 12.14.8
Reactions of methane with chlorine: 16.5.1.3
Reactions of nickel compounds: 12.9.4
Reactions of nitrates, (See: 4.)
Reactions of nitrites: 12.11.1
Reactions of non-metals with water: 12.15.4
Reactions of oxides: 12.13.0
Reactions of permanganate ion: 15.4.0
Reactions of phosphites: 12.9.5
Reactions of phosphorus and phosphates: 12.13.1
Reactions of potassium nitrate with water: 14.4.4
Reactions of potassium salts with water: 14.2.1
Reactions of salts: 12.10.10
Reactions of salts with water: 12.10.9
Reactions of sodium with water: 12.73.0
Reactions of silver compounds: 12.11.0
Reactions of silver halides: 12.19.2.6, photography
Reactions of sodium chloride: 12.19.8.1
Reactions of strontium compounds: 12.12.0
Reactions of sulfamic acid: 12.18.6.3
Reactions of dilute sulfuric acid: 12.16.2.0
Reactions of concentrated sulfuric acid: 12.16.3.0
Reactions of tin and tin compounds: 12.20.1
Reactions of urea: 16.5.4, Biuret, (See: 1.)

Rates
17.1.0 Rates of reaction
17.2.0 Rates of reaction, clock reactions
Rates of solution, (Experiments)

Recycle
Recycle chemicals: 3.4.7 See: 1.3 Recycle
Plastics recycling code, recycling symbols: 3.4.0
Recycle copper: 12.7.8
7.9.31, Recycle heavy metals safety, (Experiments)
Recycle silver: 12.10.1, (See: 6.)

Redox
Redox reactions, reduction-oxidation reactions
Redox indicators, List of redox indicators: 1.21
Redox reactions: 12.2.9
Redox reactions, Disproportionation: 17.7.16

Reduce
Reduce, reducing, reductants, reduction
In an electrolytic cell, oxidation occurs at the positively charged anode and reduction occurs at the negatively charged cathode.
Reduce carbon dioxide with burning magnesium: 3.1.1
Reduce copper oxide with natural gas methane: 16.5.1.64
Reduce metal compounds: 10.10.0
Reduce nitrate to ammonia: See 4.1
Reducing agent, Reactions of metals as reducing agents: 12.14.0
Reducing agent, Separate metals by reduction of metal oxides: 10.10.0
Reducing agents, Oxidizing agents and reducing agents: 15.4.0
Reducing sugars, tests for breakdown of starch to reducing sugars: 9.3.6
Reductants (reducing agents): 15.3.3
Reductants, List of chemical reductants: 1.22
Reduction reactions, gain of electrons: 16.1.3
Tests for reducing sugars, Benedict's test for reducing sugars: 9.4.1
Tests for reducing sugars, Fehling's test for reducing sugars: 9.5.0

Rescinnamine Rescinnamine, (C35H42N2O9), Vinca Alkaloid, anti-hypertensive, tranquillizer
It occurs in (Rauvolfia vomitoria).
See diagram: Rescinnamine.

Reserpine
Reserpine, (C33H40N2O9), Indole Alkaloid
Reserpine, indole derivative alkaloid, monoterpenoid indole alkaloid, corynanthe type alkaloid, anti-hypertensive, antipsychotic
It was used to control high blood pressure, tranquillizer, nowadays rarely used
It occurs in (Rauvolfia sepentina).
See diagram: Reserpine

Resins
Resin, (Latin: resina, Resinum from a pine)
Resins are hard, sticky, inflammable, usually aromatic substances, insoluble in water, usually collected by incisions into fir and pine trees.
They contained organic polymers and terpenoids, e.g. alpha-pinene, beta-pinene, limonene. terpinolene, caryophyllene and resin acids.
Synthetic resins, so-called, because they at first resembled natural resins, are used to make plastics are thermosetting or thermoplastic.
Rosin, colophony, gum rosin, colophonium, Greek pitch, is a solid amber residue made by the distillation of turpentine from pine stumps.
Rosin is used for adhesives, varnishes, violin bows, and contains diterpenes.
Rosins are used on the bows of violins and other stringed instruments.
Resin, ion exchange resin, anion exchange resin ("Permutit"), DOWNEX AGI-X8
Melamine-formaldehyde resins, (MF): 16.7.6.1 Cyanamides
Remove water hardness: 12.5.5
Resins and gums: 3.0.0
Resin Identification Code, Plastics recycling code: 3.4.0
Zeolite: 18.1.28
Water softening using ion exchange resin: 12.2.15

Resveratrol
Resveratrol, C14H12O3, plant polyphenol, a stilbenoid, a glycoside, a resorcinol, polyphenolic phytoalexin, antioxidant.
It is anti-diabetic, neuroprotective, antibacterial, antifungal.
It may be used to treat diabetes, atherosclerosis, aging.
It occurs in seeds of transgenic oilseed rape (Brassica napus), Japanese knotweed, red grapes skin, Polygonum, Picea, Pinus, and in Eucalyptus wandoo wood.

Retamine
Retamine, (C15H26N2O), Quinolzidine Alkaloid
Retamine, Hydroxysparteine, hypotensive, diuretic
It occurs in Genista.
See diagram: Retamine.

Retene
Retene, C18H18, methyl isopropyl phenanthrene, environmental hazard, polycyclic aromatic hydrocarbon, cytotoxic
It occurs in tars from distillation of resinous woods, and in wood pulp effluent.
It indicates conifer forest fires.

Reticuline
Reticuline, (C190H23NO4), Isoquinoline Alkaloid
Reticuline, benzylisoquinoline alkaloid, coclanoline, alkaloid precursor, (precursor of morphine)
It occurs in Papaver, Cryptocarpa, and in Romneya.
See diagram: Reticuline.

Retronecine
Retronecine, (C8H13NO2), Pyrolizidine Alkaloid, senecifolinene, pyrolizidine derivative, non-ester, may cause liver damage from excessive consumption
It occurs in (Borago officinalis), (Senecio vulgaris), (Tussilago farfara), (Heliotropium europaeum), (Echium plantagineum), and in (Crotalaria retusa).
See diagram: Retronecine.

Rhaponticin
Rhaponticin, C21H24O9, rhapontin, ponticin, a stilbenoid, antifungal.
It occurs in (Polygonum multiflorum), rhubarb, (Rheum rhabarbarum), and in Eucalyptus.

Rhein
Rhein, C15H8O6, cassic acid, rhubarb yellow, rheic acid, glucorein (rhein-8-glucoside), yellow needles or powder, cathartic.
It occurs in Rhubarb, (Rheum rhabarbarum), Polygonaceae.

Rhenium, Re
Rhenium, Table of the Elements
Rhenium, RSC
Rhenium (Latin: Rhenus 'Rhine river')

Rhodamine dyes Rhodamine B, C28H31ClN2O3
Rhodamine 6G, C28H31N2O3Cl
Rhodamine 123, C21H17ClN2O3
Rhodamine B cation, Rhodamine B(1+), Rhodamine 610, C28H31N2O3+, cationic fluorescent dye, xanthene dye.

Rhodinol
Rhodinol, C10H20O, monoterpene alcohol, floral fragrance
It occurs in citronella oil, and in lemon grass.

Rhodium, Rh
Rhodium, Table of the Elements
Rhodium, RSC
Rhodium, Rh, (Greek rhodos 'rose', from pink colour of Rh compounds), white to blue-white, hard, ductile, malleable metal
It is used in jewellery and electroplating.
C28H31N2O3Cl. Rhodium trichloride
Catalytic converter in a motor vehicle: 18.6.1

Rhodopin
Rhodopin, C40H58O, a carotenoid pigment, carotenol, tertiary alcohol
It occurs in phototrophic bacteria and in Afifella.

Rhoeadine
Rhoeadine, (C21H21NO6), rheadine, rhoeadan alkaloid, possibly antitumour, folk medicine, expectorant, sedative.
It occurs in (Papaver rhoeas).
See diagram: Rhoeadine.
Isoquinoline Alkaloid

Rhombifoline
Rhombifoline, (C15H20N2O), rhombifoline, butenylcytisine
It occurs in Genista, Ammodendron, Thermopsis, and in (Laburnum anagyroides).
See diagram: Rhombifoline.
Quinolzidine Alkaloid

Riboflavin
Riboflavin, C17H20N4O6, (Latin flavus 'yellow') Food additive E10, 1 Riboflavin, Riboflavin-5'-phosphate(vitamin B2), (In green vegetables, eggs, milk, liver), colour: orange to yellow), (in margarine)
Cassava tubers and cocoa "beans" contain riboflavin
Riboflavin, vitamin b2, Lactoflavin, Riboflavine, orange-yellow crystalline compound, a heat-stable and water-soluble flavin is a growth promoting factor.
It is the precursor of the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), is important for metabolism.
It is essential for healthy skin, nails, and hair, and it is used to treat vitamin b2 deficiency.
It occurs in babassu palm, burdock, pepper, (capsicum), Vitamin b2 complex vitamins in cereals, milk, eggs, malted barley, liver, kidney, heart, leafy vegetables.
It occurs freely in eye retina and urine.
E101 Riboflavin, Riboflavin-5'-phosphate, (vitamin b2), (in green vegetables, eggs, milk, liver), (colour: orange to yellow) (margarine)
Diet: 15.0, Bananas
Flavonoids, (Bioflavonoids)
Freezing, thawing and cold storage of meat: 19.2.5
Lost nutrients in food: 19.2.7
Pasteurization of milk: 19.2.10
Poultry composition: 12.4
Regular cows milk, fresh milk, full cream milk, whole milk: 16.2.1a
Test the cooking water of boiled vegetables: 19.2.12

Ricinine
Ricinine, (C8H8N2O2), Pyrrolidine and Piperidine Alkaloid
Ricinine, Ricidine, Ritsinin, pyridine derivative, pyridine alkaloid, pyridone, nitrile, bitter white crystals.
It may cause toxic burning feeling in mouth and throat, nausea, vomiting, severe pain in stomach, diarrhoea, reactions, hepatic and renal damage, death.
It is used as alkaloid marker for poisonous lectin ricin, e.g. in urine, toxic alkaloid, insecticidal.
It occurs in (Ricinus communis), castor seeds and leaves.
See diagram: Ricinine
Castor oil, ricinoleic acid: 16.3.6.4.

Riddelline
Riddelline, (C18H23NO6), Pyrrolizidine Alkaloid
Riddelline, is a diester of retronecine (C8H13NO2), and a possible carcinogen.
It occurs in (Senecio riddelli), (Senecio vulgaris), (Acobaea vulgaris), Crotalaria, and in Amsinckia.
See diagram: Riddelline.

Ridentin
Ridentin, C15H20O4, a germacrane sesquiterpenoid. cytotoxic, antitumour.
It occurs in Artemisia.

Rishitin
Rishitin, sesquiterpene, C14H22O2, polyol, terpenoid compound, antifungal, bacteriocidal, phytotoxic, phytoalexin.
It is produced by tubers of (Solanum tuberosum) infected by Phytophthora fungi.

Rituximab
Rituximab, C6416H9874N1688O1987S44, ia a monoclonal antibody medication.
It is used to treat non-Hodgkin lymphoma,and other conditions, by slow injection into a vein.
It works against the CD20 antigen on the surface of normal and malignant immune system B lymphocytes, to trigger cell death.
Side effects may include easy bruising, decrease in the amount of urine or unusual tiredness.
CHOP, chemotherapy used or treatment of non-Hodgkin lymphoma.
Cyclophosphamide, is an alkylating agent.
Hydroxydaunorubicin, (doxorubicin, adriamycin), is an intercalating agent.
Oncovin (vincristine), prevents cells from duplicating by binding to the protein tubulin.
Prednisone or Prednisolone, are corticosteroid component of R-CHOP21.

Rochelle salt
Rochelle salt, KNaC4H4O6.4H2O, potassium sodium tartrate tetrahydrate, Seignette salt
Seidlitz powder is a double salt of tartaric acid.
It has a saline cooling taste as a laxative, and the large deliquescent monoclinic crystals are piezoelectric and used in "crystal" phonograph pickups.
Rochelle salt: E337
Prepare Fehling's solution: 9.5.1
Tests for proteins, biuret test: 9.4.2
Piezoelectricity: Rochelle salt

Rocks
Rocks and minerals: 35.1.0
Minerals: 35.2.0
Igneous rocks: 35.2.1
Metamorphic rocks: 35.3.7
Sedimentary rocks: 35.4.5a

Roentgenium, Rg
Roentgenium, Table of the Elements
Roentgenium, RSC
Roentgenium (William Roentgen, 1845-1923, Germany, discovered X-rays), radioactive, transuranic (atomic number > 92)

Rose bengal
Rose bengal, C20H4Cl4I4O5, fluorochrome, histological dye, xanthene dye, organic potassium salt, is related to fluorescein, C20H12O5.
The sodium salt, C20H2(Cl4I4Na2O5, is used to treat eye disorders.
It is used as a stain and to treat cancers.

Rotundine
Rotundine, (C21H25NO4), Tetrahydropalmatine, Berberine Alkaloid
It is a selective dopamine D1 receptor agonist, analgesic, adrenergic agent, non-narcotic analgesic, antiprotozoal, anti-arrhythmic, sedative, tranquillizer.
It occurs in (Stephania sinica).

Rhodoxanthin
Rhodoxanthin, C40H50O2, xanthophyll carotenoid, carotenoid pigment
Food additive: E161f
Rhodoxanthin occurs in the yew tree, (Taxus baccata).

Rose oxide
Rose oxide, C10H18O, monoterpenoid, is a fragrance chemical.
It occurs in roses oil, lychee, and in Gewurztraminer wines.

Rubidium, Rb
Rubidium, Table of the Elements
Rubidium, RSC
Rubidium, Rb, (Latin rubidus red), two red lines in spectrum), is a silver-white, very reactive, alkali metal.
It occurs in pegmatites, lepidolite and pollucite.

Ruthenium, Ru
Ruthenium, Table of the Elements
Ruthenium, RSC
Ruthenium, Ru, (LatinRuthenia 'Russia'), silver-white, rare similar to platinum, catalyst, hardens alloys.
It is used in electrical contacts, platinum alloys, jewellery electroplating for "high-tech grey-black look".
Ruthenium (III chloride, Ruthenium (III) chloride hydrate, Ruthenium carbonyl

Rutherfordium, Rf
Rutherfordium, Table of the Elements
Rutherfordium, RSC
Rutherfordium (Earnest Rutherford, 1971-1937, New Zealand, later UK)
Rutherfordium is radioactive, transuranic (atomic number > 92).

Rubixanthin
Rubixanthin, C40H56O, xanthophyll carotenoid, xanthophyll pigment, Natural Yellow 27, red-orange pigment, former food colourant (E161d).
It occurs in Rose hips (Rosa canina) and Apricot (Prunus armeniaca), Rosaceae.

Rutaecarpine
Rutaecarpine, (C18H13N3O), rhetine, a pyridopyrimidine, inhibits platelet aggregation, hypotensive, vasoldilator, with strong bitter taste, is in Chinese medicine.
It occurs in (Tetradium ruticarpum), (Evodia rutaecarpa), and in (Hortia arborea).
Indole Alkaloid

Rutin
Rutin, C27H32O16, sophorin, a tetrahydroxyflavone, Rutin, sophorin, bioflavonoid is a yellow or greenish-yellow, needle-shaped crystals.
Antioxidant, strengthens capillaries to prevent bruising or bleeding, anti-inflammatory.
It prevents fat deposits in the arteries, reduces cytotoxicity of oxidized LDL-cholesterol, utilizes vitamin C to maintain collagen.
It occurs in many plants, fruits and vegetables, buckwheat, Carpobrotus, (Sophora japonica), (Ruta graveolens), Citrus, olive, lovage, dock, dill, and in fennel.
Do not take rutin if pregnant or breastfeeding.
Rutin hydrate, C27H30O16.xH2O, polyphenolic flavonoid, antioxidant, a NO scavenger, free radical scavenger, is protection against carcinogenesis.