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GCSE Chemistry > Chemical Calculations > Flashcards

Chemical Calculations Flashcards

1
Q

What does RAM stand for?

A

Relative Atomic Mass

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2
Q

Why is RAM used instead of the actual atomic mass for calculations?

A

It simplifies calculations by providing a standardized mass for elements, due to the small size of individual atomic masses.

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3
Q

What is the definition of Relative Atomic Mass?

A

The weighted average mass of the isotopes in an element.

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4
Q

Which isotope of carbon is the most common?

A

C-12

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5
Q

How is the Relative Molecular Mass (Mr) calculated?

A

Add together the Ar’s of its constituent elements

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6
Q

Calculate the Mr of CH4.

A

16

Calculation: Mr = 12 + (4x1)

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7
Q

Calculate the Mr of Ca(OH)2.

A

74

Calculation: Mr = 40 + 2(16 + 1)

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8
Q

What is a mole in terms of its atoms?

A

1 mole of hydrogen would be 1g, 1 mole of carbon would be 12g.

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9
Q

True or False: The Relative Atomic Mass of an element is a fixed number.

A

False, it varies based on the isotope it is.

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10
Q

What is the RAM of carbon?

A

12.011

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11
Q

How is the percentage mass of an element in a compound calculated?

A

Percentage mass = (Ar of element / Mr of compound) × 100

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12
Q

What is the formula for calculating the molar mass (Mr) of a compound?

A

Mr = sum of the Ar of all elements in the compound

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13
Q

Calculate the molar mass (Mr) of FeSO₄ given the atomic masses: Fe = 56, S = 32, O = 16.

A

Mr = 56 + 32 + 4(16) = 152

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14
Q

How do you calculate the percentage mass?

A

Percentage mass = (Ar of element / Mr of compound) x 100%

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15
Q

What is the percentage mass of Fe in FeSO₄?

A

Percentage mass of Fe = (Ar of Fe / Mr of FeSO₄) × 100 = (56 / 152) × 100 = 36.8%

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16
Q

What does the term ‘mole’ refer to in chemistry?

A

A mole is a unit that represents 6.02 x 10²³ particles.

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17
Q

What is Avogadro’s number?

A

Avogadro’s number is 6.02 x 10²³ particles. It is equal to 1 mole of that element.

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18
Q

What does the molar mass (Mr) represent?

A

The molar mass is equal to the mass of 1 mole of that substance.

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19
Q

Fill in the blank: 1 mole of an element is its ______ in grams.

A

Ar

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20
Q

What is the unit for molar mass?

A

g/mol

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21
Q

What does ‘Mr’ stand for in chemistry?

A

Molar mass

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22
Q

What is the relationship between mass and moles?

A

mass = moles x molar mass

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23
Q

True or False: The mass of products is equal to the mass of reactants in a chemical reaction.

A

True

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24
Q

What is the significance of the molar ratio in reacting masses calculations?

A

To calculate or deduce moles of the other species

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25
Q

Fill in the blank: No atoms are made or lost during a chemical reaction so the mass of _______ = mass of reactants.

A

products

26
Q

How can you do reacting masses calculations?

A
  • Identify the two relevant species (mass given and mass to find)
  • Calculate moles of mass given
  • Use molar ratio to find moles of other species
  • Calculate mass (moles x mr)
27
Q

In the equation ‘I Mg + 2 HCl → MgCl2 + H2’, what is the mass of H2 if the mass of Mg is 192g?

The Ar of Mg is 24, molar ratio is 1:1, and the Mr of H2 is 2

A

mass = 16

28
Q

If you know how many moles are in a substance, how can you calculate the mass?

A

mass = moles x Mr

29
Q

What does the symbol ‘Ar’ represent in chemistry?

A

Relative atomic mass

30
Q

What does ‘molar ratio’ refer to?

A

The ratio of moles of reactants to moles of products in a reaction.

31
Q

What is the definition of the empirical formula?

A

The empirical formula gives the simplest proportion of elements in a compound, but not its actual numbers.

32
Q

What is every alkene’s empirical formula?

A

CH2

33
Q

How can you calculate the empirical formula?

A
  • Calculate moles of each element
  • Work out the simplest molar ratio by dividing by the smallest number (eg 1:2:1)
  • Write the empirical formula (eg CH2O) to work out molecular formula (eg C6H12O6)
  • Calculate MF / EF and scale up your EF accordingly
34
Q

When calculating the empirical formula, if you are given a percentage of an element, what should you do?

A

Assume the percentage is the mass in grams.

35
Q

What is the formula for percentage yield?

A

percentage yield = (amount of product produced / max. amount of product possible) × 100%

36
Q

What are some reasons why percentage yield may not be 100%?

A
  • Incomplete reaction
  • Loss in transfer (some reactants left in apparatus)
  • Reaction may be reversible (products react to produce reactants again)
  • Hard to separate some products which are formed as a mixture
  • Gaseous products may escape
37
Q

What do you try to find in solution calculations?

A

The amount of solute dissolved in a volume of solvent.

38
Q

What units can be used for volume in solution calculations?

A
  • dm³
  • cm³
39
Q

What units can be used for mass in solution calculations?

A
  • grams
  • moles
40
Q

What units can be used for concentration in solution calculations?

A
  • g/dm³
  • g/cm³
  • mol/dm³
41
Q

What is the relationship between concentration, mass, and volume?

A

concentration = mass / volume

42
Q

What is 1 dm³ in cm³?

A

1 dm³ = 1000 cm³

43
Q

What is 1 dm in cm?

A

1 dm = 10 cm

44
Q

What is a reagent and what do we need them for?

A

A substance added to a mixture to make a reaction occur.

45
Q

What is a limiting reagent?

A

The reactant which is totally consumed during a chemical reaction.

46
Q

How is the product formed limited by the limiting reagent?

A

No more product can be formed as the reaction cannot continue without this reagent.

47
Q

In the reaction with 3 mol of A and 5 mol of B, which is the limiting reagent?

A

A is the limiting reagent.

This is because 3 mol of A reacts with 3 mol of B to create 3 mol of C, leaving 2 mol of unreacted B.

48
Q

What is the molar ratio in the reaction 2B + 1A → IC?

A

1:2:1

This indicates that for every 1 mol of A, 2 mol of B are required to create 1 mol of C.

49
Q

If you have 8 mol of A and 10 mol of B, how many mol of B are needed for a complete reaction, and so which is the limiting reagent.?

In a ratio of 1:2:1 (A:B:C)

A

16 mol B, so B is limiting.

The calculation is based on the ratio, where 8 mol A requires 16 mol B to fully react to make 8 mol C.

50
Q

What is the complete reaction equation for 3 mol A and 6 mol B, giving your answer in terms of C?

In a 1:2:2 ratio

A

3 mol A + 6 mol B → 6 mol C.

51
Q

What is the molar volume of a gas?

Not the actual volume, the definition

A

The volume occupied by 1 mole of any gas at the same temperature and pressure is called the molar volume.

52
Q

How many moles of any gas occupy the same volume at the same temperature and pressure?

A

1 mole of any gas occupies the same volume as and contains the same number of molecules as 1 mole of any other gas.

53
Q

Fill in the blank: The molar volume of a gas is always _______ at room temperature and pressure.

A

24 dm³ or 24,000 cm³

54
Q

True or False: The molar volume of a gas varies with the type of gas.

A

False

55
Q

What is the volume occupied by 1 mole of gas at room temperature and pressure in cm³?

A

24,000 cm³

56
Q

What is water of crystallisation?

A

Water that is chemically attached to a crystal structure.

It is found in hydrated salts like hydrated copper sulphate.

57
Q

What is the formula for hydrated magnesium chloride?

A

MgCl2 • 6H2O

This indicates that magnesium chloride is attached to six molecules of water.

58
Q

What do we call a substance with no water attached?

A

Anhydrous

59
Q

How do you find the ‘x’ in a hydrated salt?

eg. MgCl2 * xH2O

A

Find the ratio of moles of the salt to the moles of water

This involves calculations based on mass and molar mass.

60
Q

Fill in the blank: The term for the simplest molar ratio in a compound is _______.

A

Empirical formula

It represents the simplest whole-number ratio of atoms in the compound.

GCSE Chemistry (13 decks)

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