Atoms, molecules and Stoichiometry & redox

Question 1

What is proton number?

Answer 1

Number of protons in an atom

Question 2

What is nucleon number?

Answer 2

Total number of protons and neutrons in an atom

Question 3

What does relative abundance refer to?

Answer 3

The percentage of isotopes found in the naturally occurring element

Question 4

What is relative isotopic mass (Ar)?

Answer 4

The mass of one mole of atoms of an isotope relative to 1/12 the mass of one mole of 12C atoms

Question 5

What is relative atomic mass (Ar)?

Answer 5

The average mass of one mole of atoms of an element relative to 1/12 the mass of one mole of 12C atoms

Question 6

What is relative molecular mass (Mr)?

Answer 6

Average mass of one mole of molecules relative to 1/12 the mass of one mole of 12C atoms

Question 7

What is relative formula mass (Mr)?

Answer 7

Average mass of one formula unit of one mole of compound relative to 1/12 the mass of one mole of 12C atoms

Question 8

What is a formula unit?

Answer 8

Smallest group of atoms/ions from which the formula of a compound can be established

Question 9

What is the definition of Avogadro’s constant?

Answer 9

Number of 12C atoms in exactly 12g of 12C

Question 10

What is the definition of mole?

Answer 10

One mole of a substance contains exactly 6.02 * 10^23 elementary entities

Question 11

What is molar mass?

Answer 11

Mass of 1 mole of the specified substance (atoms, molecules, formula units, ions)

Question 12

What is the unit for molar mass?

Answer 12

g mol-1

Question 13

What is molar mass numerically equal to?

Answer 13

Ar and Mr

Question 14

What is the molar gas volume (Vm)?

Answer 14

The volume occupied by one mole of the substance in the gaseous state under given conditions of temperature and pressure

Question 15

What is the Avogadro’s Law?

Answer 15

Equal volumes of gases, measured under the same conditions of temperature and pressure, contain the same number of particles

V ∝ n

Question 16

How to find number of particles with the amount of substance?

Answer 16

n = number of particles / Avogadro constant

Question 17

What is empirical formula?

Answer 17

Formula of a chemical compound that shows the simplest whole-number ratio of the number of atoms of each element present in the substance

Question 18

What is molecular formula?

Answer 18

Formula of a chemical compound that shows the actual number of atoms of the different elements in one molecule in the compound

Question 19

What is the formula for percentage yield?

Answer 19

actual mass or amount of product formed/ theoretical mass or amount of product * 100%

Question 20

What is eudiometry used for?

Answer 20

To determine the molecular formulae of gaseous hydrocarbons

Question 21

What is volumetric analysis used for?

Answer 21

To determine the concentration of a solute in a given solution

Question 22

What does volumetric analysis depend on?

Answer 22

Volumes of 2 solutions which react together completely

Question 23

What is standard solution?

Answer 23

The solution whose concentration is accurately known

Question 24

What is the solution added from burette called?

Answer 24

Titrant

Question 25

What is the solution in the conical flask called?

Answer 25

Aliquot

Question 26

What is the equivalence point?

Answer 26

Point during titration at which stoichiometric amounts of reactants have reacted

Question 27

What is the end point?

Answer 27

Point during titration where indicator changes colour

Question 28

What do the end point and the equivalence point need to be in order to get accurate results?

Answer 28

As close as possible

Question 29

What is the difference between end point and equivalence point?

Answer 29

- at equivalence point only products are present - end-point may occur before/at/after equivalence point - equivalence point is independent of indicator used while end-point is dependent on indicator used

Question 30

What are the two steps in acid carbonate reaction and what is the indicator used?

Answer 30

* CO₃²⁻ (aq) + H⁺ (aq) → HCO₃⁻ (aq) * thymol blue/thymolphthalein * HCO₃⁻ (aq) + H⁺ (aq) → CO₂ (g) + H₂O (l) * methyl orange

Question 31

What is back titration?

Answer 31

Use a known amount of reagent A to react in excess with reagent B then find the amount of A unreacted through titration

Question 32

What is the definition of oxidation in terms of oxygen?

Answer 32

Gain of oxygen

Question 33

What is the definition of reduction in terms of oxygen?

Answer 33

Loss of oxygen

Question 34

What is the definition of oxidation in terms of hydrogen?

Answer 34

Loss of hydrogen

Question 35

What is the definition of reduction in terms of hydrogen?

Answer 35

Gain in hydrogen

Question 36

What is the definition of oxidation in terms of electron transfer?

Answer 36

Loss of electron

Question 37

What is the definition of reduction in terms of electron transfer?

Answer 37

Gain of electron

Question 37

What is the definition of oxidation in terms of oxidation number?

Answer 37

Increase in oxidation number

Question 37

What is the definition of reduction in terms of oxidation number?

Answer 37

Decrease in oxidation number

Question 37

What is oxidising agent?

Answer 37

A chemical species which oxidises another chemical species and itself is reduced

Question 37

What is reducing agent?

Answer 37

A chemical species which reduces another chemical species and itself is oxidised

Question 38

What are some common oxidising agents?

Answer 38

* dichromate(VI) ions in acidic medium (Cr2O₇²⁻ → Cr³⁺) * manganate(VII) ions in acidic medium (MnO₄⁻ → Mn²⁺) * manganate(VII) ions in neutral or slightly alkaline medium (MnO₄⁻ → MnO₂) * hydrogen peroxide (H₂O₂ → H₂O) * iodine (I₂ → I⁻) * iron(III) salts (Fe³⁺ → Fe²⁻)

Question 39

What are some common reducing agents?

Answer 39

- thiosulfate ions (S₂O₃²⁻ → S₄O₆²⁻) - hydrogen peroxide (H₂O₂ → O₂) - iodide ions (I⁻ → I₂) - iron(II) salts (Fe²⁺ → Fe³⁺) - ethanedioate ions (C₂O₄²⁻ → CO₂)

Question 40

What are the exceptions of the oxidation state of O?

Answer 40

* Peroxides (H₂O₂, Na₂O₂) where two oxygen atoms are linked together by a single covalent bond: -1 * Superoxides (NaO₂, KO₂) are compounds with O²⁻ ions: -1/2 * OF₂: +2

Question 41

What are the exceptions to the oxidation state of H?

Answer 41

metal hydrides (NaH, MgH₂) are compounds containing H⁻: -1

Question 42

What is disproportionation reaction?

Answer 42

A redox reaction in which one species is simultaneously oxidised and reduced

Question 43

What is used to provide the medium for manganate(VII) titrations?

Answer 43

Sulfuric acids (H₂SO₄)

Question 44

What is the end-point colour change for the titration of Fe²⁺ and MnO₄⁻ in acidic medium?

Answer 44

Yellow (Fe³⁺) to orange (mixture of yellow and pink)

Question 45

What is the colour change for dichromate(VI) titrations?

Answer 45

Orange to green

Question 46

What is used to provide the medium for dichromate(VI) titrations?

Answer 46

* H₂SO₄ and HCl * HCl can be used because K₂Cr₂O₇ is a weaker oxidising agent than KMnO₄ and cannot oxidise Cl⁻ to Cl₂

Question 47

What is the equation for iodine-thiosulfate titrations?

Answer 47

I₂ + 2S₂O₃²⁻ → 2I⁻ + S₄O₆²⁻

Question 48

Why is starch used as an indicator for iodine-thiosulfate titrations?

Answer 48

The colour change (pale yellow to colourless) at the end point is difficult to observe

Question 49

When is starch added for thiosulfate titrations and why?

Answer 49

* Near the end point * Not added to the start because when the concentration of iodine is high the blue-black colour could persist as some the iodine may remain trapped in the starch-iodine complex

Question 50

How does starch work for iodine titrations?

Answer 50

Unreacted iodine forms a blue-black complex with starch, making the colour change at the end-point

Question 51

What can iodine-thiosulfate titrations be used for?

Answer 51

* determine amount of iodine directly * add oxidising agent to KI (if the solutions contains I⁻) to liberate I₂ then titrate the liberated I₂