Chapter 3

Question 1

What’s the value of Avogadro’s constant?

Answer 1

6.02 x10^23

Question 2

What is the molar mass?

Answer 2

The mass in grams in each mole of a substance

Question 3

How do you work out moles from mass and relative formula mass?

Answer 3

n = m/mr

Question 4

What is the molecular formula?

Answer 4

The number of atoms of each element in a molecule

Question 5

What is empirical formula?

Answer 5

The simplest whole-number ratio of atoms of each element in a compound.

Question 6

What is relative molecular mass?

Answer 6

Compares the mass of a molecule with the mass of an atom of carbon-12

Question 7

What is the relative formula mass?

Answer 7

Compares the mass of a formula unit with the mass of an atom of carbon-12.

Question 8

What is a hydrated salt?

Answer 8

Water molecules are a part of the crystalline structure. White powder forms when the water is evaporated.

Question 9

What is the water in a hydrated salt called?

Answer 9

Water of crystallisation

Question 10

Assumptions made when heating hydrated salts?

Answer 10

1) All of the water has been loss (some water could be left inside) to avoid this we heat till constant mass.
2) No further decomposition (black soot could be formed) its hard to judge if there is no colour change.

Question 11

Assumptions made when heating hydrated salts?

Answer 11

1) All of the water has been loss (some water could be left inside) to avoid this we heat till constant mass.
2) No further decomposition (black soot could be formed) its hard to judge if there is no colour change.

Question 12

What formula do we use to work out moles from concentration and volume?

Answer 12

n = cv

Question 13

What is a standard solution?

Answer 13

A solution of known concentration.

Question 14

How do you produce a standard solution?

Answer 14

An exact mass of the solute is dissolved in a solvent and made up to an exact volume in a volumetric flask. It’s then inverted a few times.

Question 15

What is the molar volume (Vm)?

Answer 15

The volume per mole of gas molecules at a stated temperature and pressure.

Question 16

How do you work out the moles of a gas with the volume and molar gas volume?

Answer 16

n = V/24

molar gas volume = 24dm^3 at RTP

Question 17

What is the ideal gas equation?

Answer 17

pV=nRT

Question 18

What are all of the units used in the ideal gas equation?

Answer 18

p= Pa
V= m^3
n= mol
R= 8.314 JMol^-1K^-1 (ideal gas constant)
T= temperature (K)

Question 19

How do you go from cm3 –> m^3

Answer 19

x 10^-6

Question 20

How do you go from dm3 –> m^3

Answer 20

x10^-3

Question 21

How do you go from degrees Celsius to kelvin?

Answer 21

+ 273

Question 22

How do you go from kPa to Pa?

Answer 22

x 10^3

Question 23

What is percentage yield?

Answer 23

The actual amount of product gained from a reaction

Question 24

What is theoretical yield?

Answer 24

The maximum possible amount of product.

Question 25

How do you work out percentage yield?

Answer 25

percentage yield = actual yield/ theoretical yield x100

Question 26

What is the limiting reagent?

Answer 26

The reactant not in excess that is completely used up first and stops the reaction.

Question 27

What is atom economy?

Answer 27

A measure of how well atoms have been utilised.

Question 28

How do you work out atom economy?

Answer 28

Sum of mr of desired products/ sum of mr of all products x 100

Question 29

Why is it important to try to maximise atom economy?

Answer 29

• industrial processes are more efficient
• raw materials are preserved
• waste is reduced
• you must also take percentage yield into account