C4

Question 1

Concentration

Answer 1

The amount of a substance dissolved in a given volume of liquid

Question 2

Avogadro constant

Answer 2

The number of atoms, molecules/ions in a mole of any substance

Question 3

What is the value of Avogadro constant?

Answer 3

6.02 x 10-23 atoms/molecules/ions per mol

Question 4

Limiting reactant

Answer 4

The reactant in a chemical reaction that when used up causes the reaction to stop

Question 5

Mole

Answer 5

The amount of a substance(mass of atoms/molecules in any substance) in relative atomic/formula mass of a substance in grams/an amount of a substance containing an Avogadro number of particles/one mole of atoms/milecules in a substance has a mass in grams equal to the relative formula mass for that substance

Question 6

Relative atomic mass

Answer 6

The average mass of the atoms of an element compared with carbon-12(which has a mass of exactly 12)

Question 7

Relative formula mass

Answer 7

The total of the relative atomic masses of a substance

Question 8

Percentage mass of an element in a compound =

Answer 8

Ar x number of atoms of that element/Mr of the compound x 100

Question 9

Number of moles=

Answer 9

Mass(g)/Mr(of the element or compound)

Question 10

A mixture contains 20% iron ions by mass. What mass of iron chloride(FeCl2) would you need to provide the iron ions in 50g of the mixture? Ar of Fe=56 Ar of Cl=35.5

Answer 10

1) Find the mass of iron in the mixture:
50 x 20/100= 10g of iron
2) Percentage mass of iron in iron chloride:
56/56+2(35.5 x 100=44.09%
3) Find the mass of iron chloride containing 10g of iron:
Iron chloride has 44.09% iron by mass, so 10 divided by 44.09/100= 23g
You need 23g of iron chloride to provide the iron in 50g of the mixture

Question 11

Conservation of Mass

Answer 11

During a chemical reaction, no atoms are destroyed/created

Question 12

Reason for mass increase in an unsealed reaction vessel

Answer 12

If the mass increases, it’s because one of the reactants contained in the reaction vessel is a gas found in air, but the products are solid, liquid or aqueous

Question 13

Reasons for mass decrease in an unsealed reaction vessel

Answer 13

If the mass decreases, it’s because one of the reactants is a gas which can escape from the reaction vessel, so you can no longer account it for its mass.

Question 14

Example of mass increase in an unsealed reaction vessel

Answer 14

When a metal reacts with oxygen in an unsealed container, a metal oxide is formed so the mass of the container increases

Question 15

Example of mass decrease in an unsealed reaction vessel

Answer 15

When a metal carbonate thermally decomposes to forma metal oxide and carbon dioxide gasm the mass of the reaction vessel will decrease if it isn’t sealed.

Question 16

Balancing equations in a reaction mixture

Answer 16

1) Work out Mr for each of the substances in the reaction.
2) Divide the mass of each substance by its Mr to calculate how many moles of each substance reacted/produced.
3) Divide by the smallest number of moles.
4) The numbers are whole numbers - write the balanced symbol equation

Question 17

What are excess reactants?

Answer 17

The reactants in a reaction added in excess to make sure the other reactant is used up

Question 18

Relationship between the amount of product formed and the amount of limiting reactant

Answer 18

The amount of product formed is directly proportional to the amount of limiting reactant

Question 19

How to calculate the mass of a oroduct using the mass of the limiting reactant and the balanced reaction equation

Answer 19

1) Work out the balanced equation.
2) Work out relative formula masses of the reactant/product you want
3) Find out how many moles there are of the substance you know the mass of.
4) Find the balanced equation to work out how many roles there’ll be of the other substance.
5) Use the number of moles and Mr to calculate the mass

Question 20

Solute

Answer 20

The substance which is dissolved in a given volume

Question 21

Concentration

Answer 21

Concentration(g/dm3)= mass of solute(g)/volume(dm3)

Question 22

1cm3=

Answer 22

1000dm3