Quantitative Chemistry

Question 1

HT ONLY: State that chemical amounts are measured in moles (mol) and explain what a mol is with reference to relative formula mass and Avogadro’s constant

Answer 1

Mol - 6.02 X 10 to the power of 23 (Avogadro constant)

Relative Formula Mass - sum of all the relative atomic masses (Ar) of the atoms in the molecular formula

Question 2

HT ONLY: Calculate the masses of reactants and products when given a balanced symbol equation

Answer 2

2Mg + 02 = 2MgO

Sum of the M’rs of the reactants = Sum of the M’rs of the products

Question 3

HT ONLY: Use the relative formula mass of a substance to calculate the number of moles in a given mass of the substance

Answer 3

Number of moles (mol) = mass in g ÷ Mr (relative formula mass)

Question 4

HT ONLY: Use moles to write a balanced equation when given the masses of reactants and products (inc changing the subject of the equation)

Answer 4

Mg(s) + 2HCl(aq) = MgCl2(aq) + H2(aq)

1 mol of Mg + 2 mol of H and Cl = 1 mol of Mg and 2 mol of Cl + 2 mol of H

Question 5

HT ONLY: Explain the effect of limiting the quantity of a reactant on the amount of products in terms of moles or masses in grams

Answer 5

Limiting quantity of a reactant limits the amount of product formed so the reactions stops.

Question 6

Calculate the mass of solute in a given volume of solution of known concentration in terms of mass per given volume of solution

Answer 6

Concentration (g/dm3) = mass of volume ÷ volume of solvent

Increased amount of solvent increases concentration

Increases volume of solvent decreases concentration