Equations in reactions

Question 1

What are the masses of protons, neutrons and electrons in relative formula masses?

Answer 1

For this, we say protons and neutrons have a mass of 1 and electrons 0

Question 2

What is a mole?

Answer 2

One mole of a substance is equal to its formula mass in grams

Question 3

How do you calculate relative formula masses?

Answer 3

Add up all of the individual masses of the atoms in the formula

Question 4

How do you find the percentage mass of an element?

Answer 4

• Calculate relative formula mass
• Calculate the mass of the element you want to know the percentage mass of
• Divide the relative formula mass by the mass of the element then times by 100

Question 5

What is the empirical formula?

Answer 5

Lowest number formula for a given compound or molecule

Question 6

How do you find the empirical formula?

Answer 6

• Divide the number of atoms of each element in the formula by each’s atomic mass
• Divide everything by the smallest answer to the above calculation
• Put those numbers in the formula with their corresponding element (usually to the nearest whole number)

Question 7

What happens when you react chemicals in terms of masses?

Answer 7

Nothing is created or destroyed, just different substances are formed (Total mass of reactants = total mass of products)

Question 8

How do you calculate the mass of something formed from a particular amount of reactant (or vice versa)?

Answer 8

-Find the relative atomic mass for the substances mentioned in the question
-Divide all the above answers by the atomic mass of the substance with the given weight
-Times all of the above answers by the mass given in the question
-e.g. What mass of sulphur trioxide is formed from 96g of sulphur dioxide?
2SO2 + O2 = 2SO3
128g = 160g
1g = 1.25g ( /128)
96g = 120g ( x 96)

Question 9

What is the percentage yield?

Answer 9

The amount of product gained compared to the yield expected

Question 10

How do you calculate percentage yield?

Answer 10

actual yield
% yield = ____________ x 100
predicted yield

Question 11

Why might yield be less than expected?

Answer 11

• Lost to the surroundings
• Incomplete reactions
• Stuck to the container
• Impurities causing different reactions
• Made a different product

Question 12

Why is yield always less than 100%?

Answer 12

• Reaction is reversible so the reactants will never completely convert because the reaction goes both ways, so some of the products change back to the original reactants
• If you filter a product to remove solid particles, you nearly always lose a bit of liquid or solid
• Unexpected side reactions happen which use up reactants

Question 13

What are food additives?

Answer 13

Food additives are any substances, natural or synthetic, that are added to food to improve its taste, appearance, or another aspect

Question 14

How do you do paper chromatography?

Answer 14

• Non instrumental method
  1. Extract the colour from a sample using a solvent
  2. Put spots of the colour on a pencil baseline on filter paper
  3. Put the sheet in a beaker with solvent keeping the baseline above the solvent
  4. Solvent seeps up the paper, taking the dyes and forming spots in different places

Question 15

What does the number of dots on the filter paper after paper chromatography mean?

Answer 15

Number of dots means at least that number of dyes, not exactly that number

Question 16

How do you do gas chromatography?

Answer 16

1. Gas (mobile phase) carries substances through a column packed with solid materials (stationary phase)
2. The substances travel at different speeds depending on their solubility in the stationary phase and are separated
3. The time they take to reach the detector is the retention time and is used to identify the substances
4. A recorder draws peaks on a graph to show different compounds
5. Can link to a mass spectrometer to identify substances even more accurately

Question 17

What are the advantages of instrumental methods?

Answer 17

• Sensitive
• Fast
• Accurate

Question 18

What are the disadvantages of instrumental methods?

Answer 18

• Expensive
• Need trained personnel
• Information needs a comparator