Chapter 3

Question 1

What is the amount of substance are used to count for?

Answer 1

The number of particles in a substance measured in moles.

Question 2

What is Avogadro’s constant?

Answer 2

6.02 x 10²³ mol the number of particles in each mole of carbon 12.

Question 3

12 g of carbon-12 contains how many particles?

Answer 3

6.02 x 10²³

Question 4

What is 1 mile of any element equivalent to?

Answer 4

The relative atomic mass in grams.

Question 5

How do you work out the amount of a substance?

Answer 5

Mass/ Molar mass

Question 6

What is the molecular formula?

Answer 6

It is the number of atoms of each element in a molecule.

Question 7

What is the empirical formula?

Answer 7

It is the simplest whole number ratio of atoms of each element in a compound.

Question 8

What is the relative molecular mass?

Answer 8

It compares the mass of a molecule with the mass of an atom of carbon 12.

Question 9

What is the relative formula mass?

Answer 9

This compares the mass of a formula unit with a mass of an atom of carbon 12. It’s calculated by adding the relative atomic masses of the elements in the empirical formula.

Question 10

What is water of crystallisation?

Answer 10

Many coloured crystals are hydrated with water molecules are part of their crystalline structure.

Question 11

How is water of crystallisation indicated?

Answer 11

By a large dot

Question 12

What happens when blue crystals of hydrated copper sulphate are heated?

Answer 12

The bonds holding the water within the crystal break with water driven off leaving a white anhydrous copper sulphate.

Question 13

What happens if water is not present within the crystalline structure?

Answer 13

The structure is lost and a white powder remains. It is difficult to remove all traces of water.

Question 14

Describe the experiment for hydrated salts?

Answer 14

1. Weigh an empty crucible
2. Add the hydrated salt in the weighed crucible and weigh them both.
3. Heat the crucible which is supported by a clay triangle on a tripod. This is heated gently for 1 minute, then heated strongly for another 3 minutes.
4. Leave to cool, then reweigh the anhydrous salt and crucible.

Question 15

Is the hydrated salt experiment accurate?

Answer 15

You can only see the surface of the crystals and some water could be left inside. If both forms form similar colours it can be hard to identify. In order to improve accuracy the compound is heated to a constant mass, where the crystals are heated repeatedly until the mass of the residue no longer changes implying all water has been removed. Many salts decompose further when heated making it very difficult to judge if there is no colour change.

Question 16

What is 1 cm³ equal to?

Answer 16

1 mL

Question 17

What is 1 dm³ equal to?

Answer 17

1000 cm³ = 1000ml= 1L

Question 18

How do you calculate the amount when given concentration and volume?

Answer 18

n = c x v

n= mol
c= mol/dm³
v= dm³

Question 19

If volumes are in cm³ how do you calculate the amount?

Answer 19

n = c x v/1000

n= mol
c= mol/dm³
v=cm³

Question 20

What is the molar volume?

Answer 20

It is the volume per mole of gas molecules at a stated temperature and pressure. The volume of gas depends on the conditions but most experiments are carried at RTP.

Question 21

What is RTP?

Answer 21

It is about 20°C and 101 kPa (one atm pressure)

Question 22

At RTP how many is 1 mole equivalent to?

Answer 22

24.0dm³ = 24000 cm³

Question 23

What is the molar volume at RTP?

Answer 23

24.0 mol/dm³

Question 24

What is the ideal gas equation?

Answer 24

This equation is used when the gases are at different temperatures and pressures.

Question 25

What assumptions are made when making up an ideal gas?

Answer 25

Random motion (not influenced by each other), elastic collisions, negligible size and no intermolecular forces.

Question 26

What is the ideal gas constant?

Answer 26

8.314 JmolK

Question 27

What units is temperature in?

Answer 27

Kelvin which stops the absolute zero (-273°C). Each 1K rise is equal to 1°C rise.

Question 28

What is the equation for ideal gas?

Answer 28

pv= nRT

p= Pressure - Pa
V= Volume - m³
n= amount - mol
R= gas constant 
T= Temperature - K

Question 29

What is a standard solution?

Answer 29

A standard solution is a solution of a known concentration. Standard solutions are prepared by dissolving an exact mass of the solute in a solvent and making up the solution by an exact volume.

Question 30

What is a limiting reagent?

Answer 30

A limiting reagent is a reactive which is completely used up and stops the reaction.

Question 31

What is the maximum possible amount of product called?

Answer 31

Theoretical yield

Question 32

Why is theoretical yield hard to achieve?

Answer 32

Reactions may not be complete, side reactions could occur as well as the main reaction, purification of the product may result in a loss of product.

Question 33

How do you work out percentage yield?

Answer 33

Actual/ Theoretical x100

Question 34

What is atom economy?

Answer 34

It is a measure of how well atoms have been utilised.

Question 35

Why is it good that reactions have high atom economies?

Answer 35

As they produce a large proportion of desired products and fewer unwonted waste products. It is important in sustainability as they make best uses of natural resources.

Question 36

Why are at economy is being improved?

Answer 36

As they make industrial processes more efficient, preserve all materials and reduces waste. An ideal chemical reaction are use is found with all products thus having an atom economy of 100%.

Question 37

How do you workout atom economy?

Answer 37

sum of molar masses of desired products/ sum of molar masses of all products x 100

Question 38

What does efficiency depend on?

Answer 38

Atom economy and percentage yield.