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Chemistry > Atoms, molecules and Stoichiometry & redox > Flashcards

Atoms, molecules and Stoichiometry & redox Flashcards

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1
Q

What is proton number?

A

Number of protons in an atom

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2
Q

What is nucleon number?

A

Total number of protons and neutrons in an atom

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3
Q

What does relative abundance refer to?

A

The percentage of isotopes found in the naturally occurring element

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4
Q

What is relative isotopic mass (Ar)?

A

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

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5
Q

What is relative atomic mass (Ar)?

A

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

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6
Q

What is relative molecular mass (Mr)?

A

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

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7
Q

What is relative formula mass (Mr)?

A

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

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8
Q

What is a formula unit?

A

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

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9
Q

What is the definition of Avogadro’s constant?

A

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

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10
Q

What is the definition of mole?

A

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

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11
Q

What is molar mass?

A

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

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12
Q

What is the unit for molar mass?

A

g mol-1

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13
Q

What is molar mass numerically equal to?

A

Ar and Mr

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14
Q

What is the molar gas volume (Vm)?

A

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

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15
Q

What is the Avogadro’s Law?

A

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

V ∝ n

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16
Q

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

A

n = number of particles / Avogadro constant

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17
Q

What is empirical formula?

A

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

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18
Q

What is molecular formula?

A

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

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19
Q

What is the formula for percentage yield?

A

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

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20
Q

What is eudiometry used for?

A

To determine the molecular formulae of gaseous hydrocarbons

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21
Q

What is volumetric analysis used for?

A

To determine the concentration of a solute in a given solution

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22
Q

What does volumetric analysis depend on?

A

Volumes of 2 solutions which react together completely

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23
Q

What is standard solution?

A

The solution whose concentration is accurately known

24
Q

What is the solution added from burette called?

A

Titrant

25
Q

What is the solution in the conical flask called?

A

Aliquot

26
Q

What is the equivalence point?

A

Point during titration at which stoichiometric amounts of reactants have reacted

27
Q

What is the end point?

A

Point during titration where indicator changes colour

28
Q

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

A

As close as possible

29
Q

What is the difference between end point and equivalence point?

A
  • 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
30
Q

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

A
  • CO₃²⁻ (aq) + H⁺ (aq) → HCO₃⁻ (aq)
    * thymol blue/thymolphthalein
  • HCO₃⁻ (aq) + H⁺ (aq) → CO₂ (g) + H₂O (l)
    * methyl orange
31
Q

What is back titration?

A

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

32
Q

What is the definition of oxidation in terms of oxygen?

A

Gain of oxygen

33
Q

What is the definition of reduction in terms of oxygen?

A

Loss of oxygen

34
Q

What is the definition of oxidation in terms of hydrogen?

A

Loss of hydrogen

35
Q

What is the definition of reduction in terms of hydrogen?

A

Gain in hydrogen

36
Q

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

A

Loss of electron

37
Q

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

A

Gain of electron

37
Q

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

A

Increase in oxidation number

37
Q

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

A

Decrease in oxidation number

37
Q

What is oxidising agent?

A

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

37
Q

What is reducing agent?

A

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

38
Q

What are some common oxidising agents?

A
  • 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⁻)
39
Q

What are some common reducing agents?

A
  • thiosulfate ions (S₂O₃²⁻ → S₄O₆²⁻)
  • hydrogen peroxide (H₂O₂ → O₂)
  • iodide ions (I⁻ → I₂)
  • iron(II) salts (Fe²⁺ → Fe³⁺)
  • ethanedioate ions (C₂O₄²⁻ → CO₂)
40
Q

What are the exceptions of the oxidation state of O?

A
  • 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
41
Q

What are the exceptions to the oxidation state of H?

A

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

42
Q

What is disproportionation reaction?

A

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

43
Q

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

A

Sulfuric acids (H₂SO₄)

44
Q

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

A

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

45
Q

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

A

Orange to green

46
Q

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

A
  • H₂SO₄ and HCl
  • HCl can be used because K₂Cr₂O₇ is a weaker oxidising agent than KMnO₄ and cannot oxidise Cl⁻ to Cl₂
47
Q

What is the equation for iodine-thiosulfate titrations?

A

I₂ + 2S₂O₃²⁻ → 2I⁻ + S₄O₆²⁻

48
Q

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

A

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

49
Q

When is starch added for thiosulfate titrations and why?

A
  • 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
50
Q

How does starch work for iodine titrations?

A

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

51
Q

What can iodine-thiosulfate titrations be used for?

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

Chemistry (21 decks)

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