Calculations

Question 1

What is the Avogadro constant?

Answer 1

• N (subscript A)

- The number of particles per mole, 6.02 x 1023

Question 2

What is the molecular formula?

Answer 2

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

Question 3

What is the empirical formula?

Answer 3

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

Question 4

What does it mean if a crystal is hydrated?

Answer 4

• Water molecules are part of their crystalline structure. This water is known as water of crystallisation
• If it is anhydrous there is no water

Question 5

What is a standard solution? How would you make one?

Answer 5

• It is a solution of known concentration

- Dissolve an exact mass of the solute in a solvent and making up the solution to an exact volume

Question 6

What is a molar gas volume?

Answer 6

It is the volume per mole of gas molecules at a stated temperature and pressure, unit dm3mol-1

Question 7

What is the molar mass?

Answer 7

The mass per mole, units gmol-1

Question 8

What is meant by the stoichiometry of the reaction?

Answer 8

1. In a balanced equation, the balancing numbers give the ratio of the amount, in moles, of each substance
2. This ratio is called the stoichiometry of the reaction

Question 9

Why do you use balanced equations?

Answer 9

To find:

1. The quantities of reactants required to prepare a required quantity of a product
2. The quantities of products that should be formed from certain quantities of reactants
   - These quantities can then be changed to adjust the scale of a preparation

Question 10

17.1g of Al2(SO4)3 was dissolved in water and calculate the number of SO4 2- ions present how would you do this?

Answer 10

Moles = mass / Mr

Moles x 6.02x10^23 x 3