Topic 3 – Quantitative Chemistry (Practice Q's)

Question 1

Which two methods can be used to identify the presence of potassium ions
in potash alum solution?

Answer 1

flame emission spectroscopy

flame test

Question 2

Explain the trend in boiling points of the halogens shown in Table 1

Answer 2

(boiling point) increases (down the table / group)

(Because) the molecular mass increases

(so) the intermolecular forces increase (in strength)

(so) more energy is needed to overcome the intermolecular forces

Question 3

Why is it not correct to say that the boiling point of a single bromine
molecule is 59 °C?

Answer 3

boiling point is a bulk property

Question 4

Explain why the reactivity of the halogens decreases going down the
group.

Answer 4

(going down the group) the outer electrons/shell become further
from the nucleus

(so) the nucleus has less attraction for the outer electrons/shell

(so) an electron is gained less easily

Question 5

Explain why the excess hydrogen must be burned off.

Answer 5

to prevent hydrogen from escaping (into the air)

(Because) hydrogen is explosive

Question 6

Explain why you would not expect titanium chloride to be a liquid at room
temperature.

Answer 6

metal chlorides are usually ionic
allow titanium chloride is ionic

(so)(metal chlorides) are solid at room temperature

(because) they have strong (electrostatic) forces between the ions

Question 7

whats the percent yield calculation?

Answer 7

actual / theoretical x 100

Question 8

The reaction is carried out at a temperature of 250 °C and a pressure of
100 atmospheres.
The forward reaction is exothermic.
Explain what happens to the yield of methanol if a temperature higher than
250 °C is used.

Answer 8

smaller yield
(because) favours endothermic reaction

Question 9

A pressure of 100 atmospheres is used instead of atmospheric pressure.
The higher pressure gives a greater yield of methanol and an increased
rate of reaction.
Explain why.

Answer 9

(yield)
equilibrium position moves to the product side
(because) fewer molecules / moles / particles on product side

(rate)
more collisions per unit time
(because) more molecules / particles per unit volume

Question 10

Suggest why a catalyst is used in this industrial process

Answer 10

less energy is needed

Question 11

Suggest the effect of using the catalyst on the equilibrium yield of
methanol.

Answer 11

no effect / change

Question 12

Give a reason why it is important to use a reaction with a high atom
economy.

Answer 12

more sustainable or less waste

Question 13

how can you evaporate a flammable substance safely?

Answer 13

heat w a water bath

Question 14

Explain why the scientist adds excess zinc rather than excess iodine.

Answer 14

to make sure that all the iodine reacts
(as) excess iodine would remain in solution
(so) iodine could not be filtered off

Question 15

Suggest one reason why the percentage yield is not 100%.

Answer 15

some product lost on separation

Question 16

Describe how a sample of copper chloride crystals could be made from
copper carbonate and dilute hydrochloric acid.

Answer 16

add excess copper carbonate (to dilute hydrochloric acid)
filter (to remove excess copper carbonate)
heat filtrate to evaporate some water or heat to point of crystallisation
leave to cool (so crystals form)

Question 17

Compare the atom economies of the two reactions for making copper
chloride.
Give a reason for the difference

Answer 17

atom economy using carbonate is lower because an additional product is
made

Question 18

Why does the volume of carbon dioxide collected stop increasing at 95.0
cm3?

Answer 18

all of the acid has reacted