Topic 3 - Quantitative Chemistry

Question 1

What is the law of
conservation of mass?

Answer 1

The law of conservation of mass states that no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants

Question 2

Write a balanced equation
of magnesium reacting with
hydrochloric acid

Answer 2

Mg_(s)+ 2 HCl _(aq) → MgCl2_(aq)+ H2_(g)

Question 3

Define relative atomic mass
and relative formula mass

Answer 3

RAM - average mass of atoms in an element taking into account masses and abundance of its isotopes, relative to 12C.

RFM - sum of RAM’s of all atoms in the formula.

Question 4

What is the relative formula
mass of:
A)CaF₂

B) B) C₆H₁₂O₆

Answer 4

Question 5

The following reaction occurs in a test tube under a Bunsen
Burner:
4 MgO(s) + CH₄(g) → 4 Mg(s) + 2 H₂O(g) + CO₂(g)

The carbon dioxide and water escape from the test tube.
Use the equation to explain why

Answer 5

They are both gases

Question 6

Answer 6

(3.3 + 3.5 + 3.2) / 3 = 3.3
Measure to more decimal places or use a more sensitive balance / apparatus

Question 7

Write down the two formulae that
link concentration, mass and
volume together

Answer 7

Concentration (g per dm³) = Mass (g)/Volume (dm³)
Concentration (mol per dm³) = nr of moles/volume (dm³)

Question 8

What is the molar volume of a gas
at room temperature and
pressure?

Answer 8

1 mole of a gas at room temperature and pressure occupies 24 dm³

Question 9

What is titration?

Answer 9

A technique for finding the concentration of a solution by reacting a known volume of this solution with a solution of known concentration.

Question 10

How do you conduct a titration?

Answer 10

Question 11

Why is it not always possible to
obtain the theoretical amount of
product in a chemical reaction?

Answer 11

● The reaction may not go to completion because it is reversible.
● Some of the product may be lost when it is separated from the reaction mixture.
● Some of the reactants may react in ways different to the expected reaction (side reactions may occur)

Question 12

How is the percentage yield of
a product in a chemical
reaction?

Answer 12

Question 13

Answer 13

Question 14

What is atom economy?

Answer 14

A measure of the amount of starting materials that end up as useful products.
It is a ratio of the relative formula mass of desired product to the sum of relative formula masses of reactants

Question 15

Answer 15