3.2.2 Group 2

Question 1

Explain the trend in atomic radius of the group 2 elements

Answer 1

increases going down the group due to increasing number of electron shells

Question 2

Explain the trend in first ionisation enerfy going down group 2

Answer 2

decreases going down the group because:
- there is increased distance between the outer electron and the nucleus
- increased shielding
- decreased electostatic attraction between the outer electron and nucleus

Question 3

Explain the trend in melting point going down group 2 (Mg-Ba)

are there anomalies?

Answer 3

Generally, melting point decreases because
attraction ∝ charge/radius
and since charge remains the same but radius increases, attraction decreases.
weaker attraction between positive ions and delocalised electrons.
HOWEVER Mg is an anomaly due to a change in the
way the ions pack together.

Question 4

What is the role of Mg in the extraction of Ti?

Give thhe equations

Answer 4

Mg acts as a reducing agent in the extraction of titanium from its ore.
TiO2 + 2C + 2Cl2 –> TiCl4 + 2CO
TiCl4 + 2Mg –> Ti + 2MgCl2

Question 5

How does Magnesium react with H2O
- as liquid
- as steam

give the nature of both reactions and equations

Answer 5

as liquid (at room temp) : very slow
Mg(s) + 2H2O(l) –> Mg(OH)2(aq) + H2(g)
as steam : vigorous reaction, bright white flame
Mg(s) + H2O(g) –> MgO(s) + H2(g)

Question 6

General reaction equation for group 2 metals with water

take care with the state symbols

Answer 6

M(s) + 2H2O(l) –> M(OH)2(aq) + H2(g)

Question 7

Trend in the solubility of the group 2 hydroxides M(OH)2

Answer 7

increases going down the group, Mg(OH)2 is insoluble, Ba(OH)2 is very soluble.

Question 8

Trend in the solubility of the group 2 sulfates MSO4

Answer 8

decreases going down the group, BaSO4 is insoluble, MgSO4 is very soluble.

Question 9

What is the use of Mg(OH)2 in medicine?

Answer 9

Mg(OH)2 is used as an antacid in certain indigestion remedies.
Mg(OH)2(s) + 2HCl(aq) —> MgCl2(aq) + 2H2O(l)

Question 10

What is the use of BaSO4 in medicine?
How does it work?

Answer 10

• In medicine, an insoluble suspension of BaSO4, known as a ‘Barium meal’, is sometimes used when investigating the digestive tract using X-rays.
• The patient drinks a suspension of BaSO4 in water. X rays cannot pass through the ‘meal’, which shows up on the image.

Question 11

How come using BaSO4 is safe to consume in medicine even though Ba2+ is toxic?

Answer 11

isn’t harmful
because of the insolubility of BaSO4 in water.

Question 12

What can we use BaCl2 for?

Answer 12

BaCl2(aq) is a source of Ba2+ ions and these can be used to test for SO4 2- ions
a white precipitate is formed. This is the ionic equation:
Ba2+ (aq) + SO4 2- (aq) –> BaSO4(s)

Question 13

How does one test for SO42- ions

Answer 13

Acidified BaCl2(aq) is added to the solution being tested.
Dilute hydrochloric acid is used to acidify the solution to react with any impurities, such as aqueous carbonate or sulfite ions, which would also give a white precipitate with Ba2+ ions.

Question 14

Describe how Ca(OH)2 is used in agriculture?

Answer 14

Commonly known as ‘slaked lime’, Ca(OH)2 is used in agriculture to raise the pH of soil.

Question 15

What are CaO/CaCO3 used for?

Answer 15

CaO and CaCO3 are used to remove SO2 from flue gases in, say, coal-fired power stations.

Question 16

What are flue gases?

Answer 16

Gases produced by power stations which are harmful to the environment.

Question 17

How do CaO/CaCO3 remove SO2 from flue gases?

Answer 17

SO2 is acidic and CaO or CaCO3 act as bases to neutralise it

Question 18

Write the equation for the reaction of CaO with SO2

Answer 18

CaO(s) + SO2(g) –> CaSO3(s)

Question 19

Write the equation for the reaction of CaCO3 with SO2

Answer 19

CaCO3(s) + SO2(g) –> CaSO3(s) + CO2(g)