CC9

Question 1

What is an empirical formula?

Answer 1

The formula showing the simplest whole number ratio of each element in a compound.

Question 2

What is a molecular formula?

Answer 2

The formula showing the actual number of atoms of each element in a molecule of a compound.

Question 3

How do you work out the empirical formula of a compound?

Answer 3

You need to divide the number of atoms of each element in a compound until it is in its simplest form (e.g. C₂H₆ = CH₃, C₂H₄O₂ = CH₂O).

Question 4

What is the relative formula mass(Mᵣ) of a substance?

Answer 4

The sum of the relative atomic masses(Aᵣ) of all the atoms or ions in its formula (e.g. Mᵣ of Ca(NO₃)₂ = Aᵣ(Ca) + 2(Aᵣ(N) + (3 x Aᵣ(O))) = 40 + 2(14 + (3 x 16)) = 164).

Question 5

How do you find the empirical formula of a substance?

Answer 5

You need to make a table with the following rows:
1. Mass(g) of elements
2. Relative atomic mass (Aᵣ)
3. Mass(g) / Relative atomic mass(Aᵣ)
4. Divide the answer of that by the smaller of the two answers
5. Empirical formula
(Multiply each number of empirical formula to whole number to find simplest whole number ratio if there are decimals)

Question 6

What is the law of conservation of mass?

Answer 6

The idea that mass is never lost or gained during a chemical reaction or physical change.

Question 7

What is a solution’s concentration?

Answer 7

The amount of solute dissolved in a stated volume of a solution.

Question 8

What is the unit for concentration?

Answer 8

Grams per cubic decimetre(gdm⁻³)

Question 9

What is the equation for concentration?

Answer 9

Concentration(gdm⁻³) = Mass of solute(g) / Volume of solution (dm³)

Question 10

What is the unit conversion from cm³ to dm⁻³?

Answer 10

You can convert cm³ to dm⁻³ by dividing the cm³ by 1000.

Question 11

What is a closed system in a reaction?

Answer 11

When no new substances are added or removed during a reaction as substances cannot enter or leave an observed environment (e.g. stoppered test tube)

Question 12

What is a non-enclosed system in a reaction?

Answer 12

When gas can escape the reaction so the mass appears to have decreased after the reaction.

Question 13

What happens to some solids when heated in a non-enclosed system?

Answer 13

Some solids appear to gain in mass when they are heated in a non-enclosed system.

Question 14

What is the Avogadro constant?

Answer 14

The number of particles in one mole of a substance (6.02 x 10²³ mol⁻¹).

Question 15

What is the unit for mole?

Answer 15

mol.

Question 16

What is the mass of one mole of a substance?

Answer 16

The mass of one mole of a substance is the relative atomic mass(Aᵣ) or relative formula mass(Mᵣ) in grams.

Question 17

What is the equation for calculating the number of moles in a substance?

Answer 17

Number of moles of a substance = Mass of substance(g) / Aᵣ or Mᵣ

Question 18

What does a balanced equation show in terms of moles?

Answer 18

A balanced equation shows the ratios of the substances in moles (e.g. 2Mg + O₂ –> 2MgO shows that 2 mol of magnesium reacts with 1 mol of oxygen to form 2 mol of magnesium oxide).

Question 19

Why do you usually burn magnesium in excess during an experiment(2Mg + O₂)?

Answer 19

To make sure that all the magnesium reacts with the Oxygen.

Question 20

What is a limiting reactant?

Answer 20

The reactant that determines the amount of product formed in a chemical reaction. Any other reactants will be present in excess.

Question 20

What is the stoichiometry of a reaction?

Answer 20

The molar ration of the reactants and the products in a chemical reaction.