Amount of Substance

Question 1

Define a mole.

Answer 1

1. Amount of a substance (N) that contains 6.022 x 10^23 particles
2. Measured in mol

Question 2

What is Avagadro’s constant?

Answer 2

1. 6.022 x 10 ^23 (Nₐ)

2. Number of particles in one mole

Question 3

What is the unit of molar mass?

Answer 3

g mol⁻¹

Question 4

What is the formula for moles?

Answer 4

Moles = mass/molar mass

Question 5

What is the difference between empirical and molecular formula

Answer 5

1. Molecular = No of atoms of each element in a molecule

2. Empirical = Simplest whole no ratio of atoms in a compound.

Question 6

Define molecule.

Answer 6

A NEUTRAL particle made up of 2 or more covalently bonded atoms

Question 7

Why don’t ionic compounds and metals have molecular formulas?

Answer 7

They form giant structures which are not molecules.

Question 8

What is the difference between relative MOLECULAR mass and relative FORMULA mass?

Answer 8

1. RMM = weighted mean mass of a MOLECULE relative to 1/12 of the mass of an atom of carbon-12
2. RFM = mass of a formula unit relative to mass of an atom of carbon-12

Question 9

How do you work out the molecular formula from the empirical formula?

Answer 9

1. Calculate RMF from EF
2. Divide molecular mass by RFM to find factor
3. Multiply each atom in EF by factor