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AQA A Level Physical Chemistry > 2. Amount Of Substance > Flashcards

2. Amount Of Substance Flashcards

1
Q

Why are all mass relative to carbon-12?

A

1/12 of its relative atomic mass is 1

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2
Q

How can relative atomic mass (Ar) be defined?

A

The weighted average mass of an atom of an element, taking into account its isotopes, relative to 1/12 of the relative atomic mass of an atom of carbon-12

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3
Q

How can relative atomic mass be calculated?

A

average mass of one atom of an element / 1/12 mass of one atom of carbon-12

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4
Q

How can relative molecular mass (Mr) be defined?

A

The mass of that molecule compared to 1/12 of the relative atomic mass of an atom of carbon-12

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5
Q

How can relative molecular mass be calculated?

A

average mass of one molecule / 1/12 mass of one atom of carbon-12

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6
Q

What do ionic compounds exist as instead of molecules?

A

Ionic lattices

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7
Q

What is used for ionic compounds instead of relative molecular mass?

A

Relative formula mass

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8
Q

Why is relative formula mass used for ionic compounds?

A

They form ionic lattices instead of molecules

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9
Q

What does the formula of an ionic compound show?

A

The simplest ratio of ions in the compound

instead of the total number of atoms in the compound

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10
Q

What is the mole defined as?

A

The amount of substance that contains 6.022e23 particles

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11
Q

How many particles are in one mole of a subtance?

A

6.022e23 (electrons, atoms, molecules, ions or compounds)

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12
Q

What equation is used to work out number of moles (using mass and mr)?

A

n = mass / mr

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13
Q

What is the final answer usually given to?

A

3 significant figures

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14
Q

How many decimal places should Mr be calculated to?

A

1

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15
Q

What is the concentration of a solution?

A

The amount of solute present in a fixed quantity of solvent

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16
Q

What is concentration measured in?

A

g/dm³ or mol/dm³

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17
Q

What is the molarity?

A

The concentration (in mol/dm³)

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18
Q

How can number of moles be calculated (when given conc. and volume)?

A

n=cv

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19
Q

g/dm³ to mol/dm³?

A

÷ Mr

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20
Q

mol/dm³ to g/dm³?

A

x Mr

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21
Q

What is a titration?

A

The procedure of reacting volumes

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22
Q

During a titration, what is placed in the burette?

A

The solution of known concentration

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23
Q

During a titration, what is placed in the conical flask?

A

The solution of unknown concentration

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24
Q

What is the law of conservation of mass?

A

Mass of reactants = Mass of products

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25
Q

What does the volume a gas occupies depend on?

A
  • temperature
  • pressure
  • amount of gas
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26
Q

How does the temperature of a gas influence the volume it occupies?

A

The hotter the gas, the faster the particles move and the more space they occupy

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27
Q

How does the pressure of a gas influence the volume it occupies?

A

The higher the pressure, the more compressed the gas will be and the less space it will occupy

28
Q

How does the amount of a gas influence the volume it occupies?

A

The more gas particles there are, the more space they will occupy

29
Q

What is the ideal gas law?

A

One mole of any gas, at the same temperature and pressure, will have the same volume as one mole of any other gas

30
Q

What is the equation for the ideal gas law?

A

PV = nRT

31
Q

What is pressure measured in for the ideal gas equation?

A

Pa

32
Q

What is volume measured in for the ideal gas equation?

A

m³

33
Q

What is the gas constant measured in for the ideal gas equation?

A

J/K mol

34
Q

What is temperature measured in for the ideal gas equation?

A

kelvin, K

35
Q

How to convert from degrees to kelvin?

A

add 273

36
Q

What is the value of the gas constant, R, in the ideal gas equation?

A

8.31 J/K mol

37
Q

What is 1 atm equal to?

A

100,000 Pa

38
Q

What is the empirical formula of a compound?

A

The formula which shows the simplest, whole-number ratio of the atoms in the compound

39
Q

What is the molecular formula of a substance?

A

The formula which shows the number of each type of atom in the one molecule of that substance

40
Q

What is the molecular formula, relative to the empirical formula?

A

The molecular formula is always a simple, whole-number multiple of the empirical formula (and therefore can be the same as the empirical formula)

41
Q

Why can the percentage of each element in a compound be used as the mass ratio?

A

As the empirical formula is a ratio

42
Q

What can you use if you are not given mass ratios when working out empirical formula?

A

The percentage of each element in a compound

43
Q

How to work out empirical formula?

A
  • Find mole ratio by doing mass/mr for each substance in compound
  • divide by smallest value
  • round if near number, if not multiply all to get a whole number ratio
44
Q

How can molecular formula be found from empirical formula?

A

Divide Mr of the compound by Mr of the empirical formula`

45
Q

What does a chemical reaction equation show?

A
  • the identities of all the reactants and products
  • the reaction coefficients
  • state symbols
46
Q

When balancing equations, what should be done with unchanged species?

A

They should be left out e.g. catalysts

47
Q

What should be balanced first in equations?

A

Compounds first; elements second

48
Q

What does a state symbol show?

A

The physical state of each species in the reaction e.g. s, l, g, aq

49
Q

What are compounds of ions known as?

A

Salts

50
Q

Do salts form molecules?

A

No - they form giant ionic lattices

51
Q

Why is the formula representing salts not a molecular formula?

A

They form giant ionic lattices instead of molecules, so a represented using a unit formulae

52
Q

What is the unit formula of an ionic compound?

A

The formula that shows the simplest whole number ratio in which the ions in the compound exist

53
Q

What are the ions called that remain in aqueous solution before and after the reaction?

A

Spectator ions

54
Q

In ionic equations, if an insoluble ionic compound is produced, is the formula written as ions?

A

No - the ions are not free to move

55
Q

What are ionic equations useful for?

A
  • to simplify precipitation reactions

* to simplify acid-base reactions

56
Q

Do all reactions between strong acids and alkalis have the same ionic equation?

A

Yes

57
Q

Can covalent compounds be ‘split up’ in ionic equations?

A

No - they do not contain ions

58
Q

What is percentage yield?

A

A comparison of the theoretical maximum yield and the actual yield

59
Q

What is atom economy?

A

The percentage of the total mass of reactants that can be converted into the desired product

60
Q

How is percentage yield calculated?

A

(Actual amount of product ÷ theoretical amount of product) x 100

61
Q

What quantities are used when calculating percentage yield?

A

mols or grams

62
Q

Why is percentage yield always less than theoretical maximum?

A
  • some reactions are reversible - not all reactants end up as products
  • in some reactions products must be isolated from other unwanted products (and some desired products may be lost in isolation methods)
  • some reactions may produce products that go on to produce additional reactions
63
Q

How is atom economy calculated?

A

(Mr of desired products ÷ sum of molecular mass of all reactants) x 100

64
Q

In which of atom economy and percentage yield do you have to pay attention to the coefficient before formulae?

A

Atom economy

65
Q

Advantages of having a higher atom economy?

A

economic - more efficient use of raw materials, and less money wasted from producing unwanted by-products from reactants

environmental - produce less waste, and some products are harmful to the environment (high atom economy means less of these products are produced)

AQA A Level Physical Chemistry (12 decks)

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