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AQA GCSE Chemistry > 3. Quantitative Chemistry > Flashcards

3. Quantitative Chemistry Flashcards

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
How is Mr calculated? (mass and mol)
Mass / Mol
26
How is mol calculated? (mass and mr)
Mass / Mr
27
If you wanted to calculate the mass of a neutron relative to the mass of a proton, how would you do it?
Divide the neutron mass number by the proton mass number (which happens to equal 1, by the way)
28
What is the coefficient in a chemical equation proportional to?
The number of moles
29
Why would knowing the molar (stoichiometric) ratio be useful for a chemist to know how much of a reactant he needs?
He can calculate the mass of reactant needed using mass = mr x mol
30
What are the 3 steps to balance an equation using moles?
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
31
What is the limiting reactant?
When the number of moles of a reactant is less than the stoichiometric ratio
32
What does the limiting reactant limit?
How far the reaction progresses i.e. the reaction will not go to completion
33
Why may it not always be possible to obtain the calculated amount of product?
* 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
What is the yield?
The amount of a product obtained
35
What the is percentage yield?
When the actual amount of product obtained is compared to the theoretic amount as a percentage
36
What is the theoretical maximum?
The amount calculated using mass = mr x mol and if the reaction went fully to completion
37
How to calculate percentage yield?
Actual amount / Theoretical yield x 100
38
What is atom economy a measure of?
The amount of starting materials that end up as useful products
39
Why should reactions have a high atom economy?
For sustainable development and economic reasons
40
How is atom economy calculated?
Mr of desired product / Sum of Mr of all reactants x 100
41
What happens in atom economy equations that doesn't happen in any other?
The Mr and coefficients are multiplied together
42
When calculating what do you multiply the Mr and coefficients together?
Atom economy
43
What are the chemical units of volume?
dm3
44
What is 1 dm3 equal to in litres?
1 litre
45
What is 1 dm3 equal to in cm3?
1000 cm3
46
How do you convert cm3 to dm3?
Divide by 1000
47
How is concentration (g/dm3) calculated?
Quantity of solute / volume
48
How can the quantity of a solute be calculated?
Concentration x volume
49
What is the equation that links concentration, quantity of solute and volume?
Concentration (g/dm3) = quantity (g) / volume (dm3)
50
What happens to concentration if volume is doubled?
The concentration is halved
51
What is the most common measure of concentration?
mol/dm3
52
Why do chemists prefer to use mol/dm3 when calculating concentration?
So they can use the molar stoichiometry of balanced equations
53
How do you convert from mol/dm3 to g/dm3?
Multiply by Mr
54
How do you convert from g/dm3 to mol/dm3?
Divide by Mr
55
How is concentration calculated using moles?
Concentration = mol / volume
56
How is the number of moles calculated using concentration?
concentration x volume | n=cv
57
What is the symbol equation for calculating concentration in mol/dm3?
n=cv
58
When calculating concentration with moles, what MUST the volume be in?
dm3
59
Factors that should be considered when choosing a method make a product?
* atom economy * percentage yield * reaction rate * reversibility * energy cost * cost of reactants * whether undesirable products can be sold/used
60
What do acids do when they are part of a solution?
Ionise to release H+ ions
61
What happens to pH when there is a higher concentration of H+ ions?
pH is lowered (more acidic)
62
What happens to pH when there is a lower concentration of H+ ions?
pH is raised (less acidic)
63
Is HCl a strong or weak acid?
Strong
64
Why is HCl is strong acid?
Every molecule fully ionises
65
How many molecules in weak acid ionise?
Few of them - partially ionises
66
Is ethanoic acid a strong or weak acid?
Weak - pH 3
67
Is nitric acid a strong or weak acid?
Strong - pH 1
68
Is citric acid a strong or weak acid?
Weak - pH 3
69
Is carbonic acid a strong or weak acid?
Weak - pH 4
70
Is hydrochloric acid a strong or weak acid?
Strong - pH 1
71
Is sulphuric acid a strong or weak acid?
Strong - pH 1
72
What type of scale does the pH scale use?
Logarithmic
73
What was Avogadro's law about the molar volume of a gas?
1 mol of any gas at room temperature and pressure occupies a volume of 24dm3
74
In Avogadro's gas law, what is room temperature?
25*C
75
In Avogadro's gas law, what is room pressure?
1 atm
76
How much volume does 1 mol of a gas at room temperature and pressure occupy?
24dm3
77
Equation to find the volume of a known gas at room temperature and pressure?
Volume of gas = (Mass of gas / Mr of gas) x 24
78
How much CO2 is formed when 30dm3 of oxygen reacts with carbon monoxide? (2CO + O2 -> 2CO2)
1 mol of O2 makes 2 mols of CO2, so 30dm3 produces 60dm3 of CO2

AQA GCSE Chemistry (10 decks)

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