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AQA GCSE Chemistry > 3. Quantitative Chemistry > Flashcards

3. Quantitative Chemistry Flashcards

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1
Q

Why do chemists need to know how to write and balance equations?

A
  • know the quantity of products
  • know the quantity and proportions of reactant they’ll need
  • determine quantity of waste product
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2
Q

What happens to mass during a reaction?

A

It is conserved

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3
Q

What is relative formula mass?

A

The sum of the relative atomic masses of each atom in a compound

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4
Q

What can relative formula mass be shortened to?

A

Mr

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5
Q

Why is there always uncertainty when results are obtained?

A

Due to errors

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6
Q

How to avoid a measurement error when using a measuring cylinder?

A
  • measure from bottom on meniscus

* measure from eye level

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7
Q

What does judging the meniscus from eye level prevent?

A

A parallax error

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8
Q

What has to be ensured when using a gas syringe so no gas escapes?

A

That it is sealed tightly

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9
Q

What is a zero error when using a gas syringe?

A

When the gas syringe has not been set back to zero before taking the measurement

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10
Q

How can a zero error be prevented?

A

By setting the gas syringe or top pan balance back to zero before taking a reading

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11
Q

What is the result of a zero error?

A

A measurement appears larger than it actually is

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12
Q

What can disruptions to measurements when using a top pan balance be due to?

A
  • other people (e.g. leaning on table)
  • wind/breeze
  • contamination (e.g. already powder on balance)
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13
Q

How can contamination of a top pan balance be avoided?

A

By cleaning balance with a soft brush

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14
Q

What are some reasons for uncertainty when collecting measurements?

A
  • product/reactant is impure
  • losses have occurred
  • sample is wet
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15
Q

How can a product or reactant being impure affect certainty of measurements?

A

Less than 100% of the recorded mass is what you think it is

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16
Q

How can losses occurring affect the certainty of measurements?

A

Products like gases can escape easily, and solid powders can be blown away

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17
Q

How can a sample being wet affect the certainty of measurements?

A

Water can contaminate solids, so they appear heavier

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18
Q

What does the range do?

A

Represents the distribution of results

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19
Q

How is uncertainty shown using the mean and range?

A

Uncertainty = mean +/- furthest away figure from mean

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20
Q

How is percentage uncertainty calculated?

A

Range / Mean x 100

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21
Q

How many atoms, molecules or ions are in 1 mole?

A

6.02x10 to the power of 23

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22
Q

If you have 1 mole of an element, how much will it weigh?

A

The relative atomic mass in grams

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23
Q

How many atoms are in 12g - its relative atomic mass - of carbon?

A

6.02x10 to the power of 23

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24
Q

How is mass calculated? (Mr and mol)

A

Mr x Mol

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25
Q

How is Mr calculated? (mass and mol)

A

Mass / Mol

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26
Q

How is mol calculated? (mass and mr)

A

Mass / Mr

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27
Q

If you wanted to calculate the mass of a neutron relative to the mass of a proton, how would you do it?

A

Divide the neutron mass number by the proton mass number (which happens to equal 1, by the way)

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28
Q

What is the coefficient in a chemical equation proportional to?

A

The number of moles

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29
Q

Why would knowing the molar (stoichiometric) ratio be useful for a chemist to know how much of a reactant he needs?

A

He can calculate the mass of reactant needed using mass = mr x mol

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30
Q

What are the 3 steps to balance an equation using moles?

A
  1. Divide mass by Mr to calculate number of moles of each substance
  2. Divide each number of moles by the smallest to determine the ratio
  3. Molar ratio = coefficients in equation
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31
Q

What is the limiting reactant?

A

When the number of moles of a reactant is less than the stoichiometric ratio

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32
Q

What does the limiting reactant limit?

A

How far the reaction progresses i.e. the reaction will not go to completion

33
Q

Why may it not always be possible to obtain the calculated amount of product?

A
  • reaction may not go to completion because it’s reversible
  • some product lost when being separated from reaction mixture
  • some reactants may react different to expected
34
Q

What is the yield?

A

The amount of a product obtained

35
Q

What the is percentage yield?

A

When the actual amount of product obtained is compared to the theoretic amount as a percentage

36
Q

What is the theoretical maximum?

A

The amount calculated using mass = mr x mol and if the reaction went fully to completion

37
Q

How to calculate percentage yield?

A

Actual amount / Theoretical yield x 100

38
Q

What is atom economy a measure of?

A

The amount of starting materials that end up as useful products

39
Q

Why should reactions have a high atom economy?

A

For sustainable development and economic reasons

40
Q

How is atom economy calculated?

A

Mr of desired product / Sum of Mr of all reactants x 100

41
Q

What happens in atom economy equations that doesn’t happen in any other?

A

The Mr and coefficients are multiplied together

42
Q

When calculating what do you multiply the Mr and coefficients together?

A

Atom economy

43
Q

What are the chemical units of volume?

A

dm3

44
Q

What is 1 dm3 equal to in litres?

A

1 litre

45
Q

What is 1 dm3 equal to in cm3?

A

1000 cm3

46
Q

How do you convert cm3 to dm3?

A

Divide by 1000

47
Q

How is concentration (g/dm3) calculated?

A

Quantity of solute / volume

48
Q

How can the quantity of a solute be calculated?

A

Concentration x volume

49
Q

What is the equation that links concentration, quantity of solute and volume?

A

Concentration (g/dm3) = quantity (g) / volume (dm3)

50
Q

What happens to concentration if volume is doubled?

A

The concentration is halved

51
Q

What is the most common measure of concentration?

A

mol/dm3

52
Q

Why do chemists prefer to use mol/dm3 when calculating concentration?

A

So they can use the molar stoichiometry of balanced equations

53
Q

How do you convert from mol/dm3 to g/dm3?

A

Multiply by Mr

54
Q

How do you convert from g/dm3 to mol/dm3?

A

Divide by Mr

55
Q

How is concentration calculated using moles?

A

Concentration = mol / volume

56
Q

How is the number of moles calculated using concentration?

A

concentration x volume

n=cv

57
Q

What is the symbol equation for calculating concentration in mol/dm3?

A

n=cv

58
Q

When calculating concentration with moles, what MUST the volume be in?

A

dm3

59
Q

Factors that should be considered when choosing a method make a product?

A
  • atom economy
  • percentage yield
  • reaction rate
  • reversibility
  • energy cost
  • cost of reactants
  • whether undesirable products can be sold/used
60
Q

What do acids do when they are part of a solution?

A

Ionise to release H+ ions

61
Q

What happens to pH when there is a higher concentration of H+ ions?

A

pH is lowered (more acidic)

62
Q

What happens to pH when there is a lower concentration of H+ ions?

A

pH is raised (less acidic)

63
Q

Is HCl a strong or weak acid?

A

Strong

64
Q

Why is HCl is strong acid?

A

Every molecule fully ionises

65
Q

How many molecules in weak acid ionise?

A

Few of them - partially ionises

66
Q

Is ethanoic acid a strong or weak acid?

A

Weak - pH 3

67
Q

Is nitric acid a strong or weak acid?

A

Strong - pH 1

68
Q

Is citric acid a strong or weak acid?

A

Weak - pH 3

69
Q

Is carbonic acid a strong or weak acid?

A

Weak - pH 4

70
Q

Is hydrochloric acid a strong or weak acid?

A

Strong - pH 1

71
Q

Is sulphuric acid a strong or weak acid?

A

Strong - pH 1

72
Q

What type of scale does the pH scale use?

A

Logarithmic

73
Q

What was Avogadro’s law about the molar volume of a gas?

A

1 mol of any gas at room temperature and pressure occupies a volume of 24dm3

74
Q

In Avogadro’s gas law, what is room temperature?

A

25*C

75
Q

In Avogadro’s gas law, what is room pressure?

A

1 atm

76
Q

How much volume does 1 mol of a gas at room temperature and pressure occupy?

A

24dm3

77
Q

Equation to find the volume of a known gas at room temperature and pressure?

A

Volume of gas = (Mass of gas / Mr of gas) x 24

78
Q

How much CO2 is formed when 30dm3 of oxygen reacts with carbon monoxide? (2CO + O2 -> 2CO2)

A

1 mol of O2 makes 2 mols of CO2, so 30dm3 produces 60dm3 of CO2

AQA GCSE Chemistry (10 decks)

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