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Chemistry A-Level > Calculations, Formulae and Relative Mass (2.3 + Chapter 3) > Flashcards

Calculations, Formulae and Relative Mass (2.3 + Chapter 3) Flashcards

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1
Q

From mass to moles?

A 
n = m / Mr
m = n x Mr
Mr = m / n
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2
Q

Units of n?

A

mols

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3
Q

Units of m?

A

g

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4
Q

Units of Mr?

A

gmol-1

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5
Q

From concentration to moles?

A 
n = c x v 
c = n / v
v = n / c
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6
Q

Units of c?

A

moldm-3

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7
Q

Units of v?

A

dm-3

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8
Q

How to convert from concentration in gdm-3 to concentration in moldm-3?

A

c (gdm-3) = c (moldm-3) x Mr (gmol-1)

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9
Q

From gas volumes to moles?

A 
n = V / 24
V = n x 24
24 = n / V  *at RTP/STP
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10
Q

What is the ideal gas law equation?

A

pV = nRT *not at RTP/STP

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11
Q

What is the value of p, V, n, R and T in the ideal gas law equation?

A 
p = Pa
v = m3
n = mol
R = 8.31
T = K
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12
Q

What is the equation for atom economy?

A

(Sum of the Mr of desired products / sum of Mr of all products) x 100

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13
Q

What is the equation for yield?

A

(actual yield / expected yield) x 100

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14
Q

What is important to remember about the atom economy equation?

A

To include molar ratio numbers in calculation the equations e.g. Mr of 2Na = 2 x 23 = 46

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15
Q

What is the limiting reagent (i.e the reagent to use in mols ratio)?

A

The reactant that is not in excess which will be completely used up first and stop the reaction

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16
Q

How do you convert cm3 to m3?

A

x 10^-6

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17
Q

How do you convert dm3 to m3?

A

x 10^-3

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18
Q

How do you convert degreesC to K?

A

+ 273

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19
Q

How do you convert kPa to Pa?

A

x 10^3

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20
Q

What is the Vm constant?

A

24dm3mol-1 or 24,000cm3mol-1

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21
Q

How do you convert atm to Pa?

A

x 101,325

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22
Q

What is 0.98atm equal to?

A

100,000 Pa

23
Q

What assumptions does the ideal gas law make?

A

1) Random motion
2) Elastic collisions
3) Negligible size
4) No IM forces

24
Q

What is the empirical formula?

A

The simplest whole number ratio of atoms of each element present in a compound

25
Q

What is the molecular formula?

A

The number and type of atoms of each element in a molecule

26
Q

What is the Avogadro’s constant (NA)?

A
  1. 02 x 10^23 mol-1

- The number of particles in each mole of carbon-12

27
Q

How would you find out the number of particles in a substance?

A

6.02 x 10^23 x number of moles

28
Q

What is a binary compound?

A

A compound that contains 2 elements only

29
Q

What are polyatomic ions?

A

Ions containing atoms of more than one element bonded together

30
Q

What does aqueous mean?

A

Dissolved in water

31
Q

What is the formula unit?

A

The formula worked out from the ionic charges

32
Q

What is the amount of substance (n)?

A

A quantity used to count the number of particles in a substance, measured in mols

33
Q

What is one mole?

A

The amount of substance that contains 6.02x10^23 particles

34
Q

What is the molar mass?

A

The mass per mole of a substance

35
Q

What are the units of molar mass?

A

g/mol

36
Q

What is the molar gas volume?

A

The volume per mole of gas molecules at a stated temperature and pressure

37
Q

What are the units of molar gas volume?

A

dm3/mol

38
Q

What is the relative molecule mass (Mr)?

A

Compares the mass of a molecule with the mass of an atom of carbon-12

39
Q

What is the relative formula mass?

A

Compares the mass of a formula unit with the mass of an atom of carbon-12

40
Q

What does hydrated mean?

A

That water molecules are part of the crystalline structure of a crystal

41
Q

What is the water of crystallisation?

A

The water molecules that are part of the crystalline structure

42
Q

What does anhydrous mean?

A

That the bonds holding together the water within the crystal are broken and the water is driven off

43
Q

What assumptions are you making when you dehydrate a hydrated crystal?

A

1) All of the water has been lost

2) There has been no further decomposition

44
Q

What is one dm3 equal to?

A

1 litre

45
Q

What is RTP

A

20 degrees and 101kPa (1atm)

46
Q

What is the molar gas volume at RTP?

A

24 dm3/mol

47
Q

What is the stoichiometry of a reaction?

A

The ratio of the amount, in moles, of each substance in a balanced equation

48
Q

Why is it difficult to achieve the theoretical yield of a reaction?

A

1) The reaction may not have gone to completion
2) Side reaction may have taken place
3) Purification of the product may result in some loss of the product

49
Q

How do you work out which reactant is in excess?

A

1) Working out the amount in moles of each reactant and comparing with the equation
2) Calculations must be based on the limiting reagent (i.e. use this in moles ratio)
- e.g. when hydrogen and oxygen react to form water, 2 mol of hydrogen are required for every 1 mole of oxygen
- therefore, if equal amounts of hydrogen and oxygen are allowed to react, hydrogen will be used up first, and half the oxygen will be unreacted
- the limiting reagent is therefore hydrogen

50
Q

What is the atom economy?

A

A measure of how well atoms have been utilised

51
Q

What do reactions with high atom economies produce?

A

A large proportion of desired products and few unwanted waste products

52
Q

What are reactions with high atom economies important for?

A

Sustainability as they make the best use of natural resources

53
Q

What are the benefits for sustainability for developing chemical processes with a high atom economy?

A

1) Makes industrial processes more efficient
2) Preserves raw materials
3) Reduces waste

Chemistry A-Level (27 decks)

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