Group 2

Question 1

Why do the group 2 metals become more reactive as you go down the group?

Answer 1

• as you go down the group, the number of electron shells increases, and atomic radius increases
• outer e- is further from the nucleus, and experiences more shielding
• so weaker force of attraction between the outer e- and the nucleus
• so outer e- is more easily lost

Question 2

Explain why the melting point of strontium (Sr) is less than that of magnesium (Mg)

Answer 2

• Sr has a greater number of e- shells than Mg, and greater atomic radius
• outer e-s are further from nucleus, and have greater shielding
• so the electrostatic force of attraction between positive ions and delocalised electrons decreases
• easier to overcome this weaker metallic bonding

Question 3

Describe the reaction of group 2 metals with oxygen.

Answer 3

-They all burn with a bright white flame
-They all react with oxygen in the air to make a coating of MO on the surface of the metal
-2M + O2 -> 2MO

Question 4

This question is about the group 2 metals.
When calcium metal is added to cold water, a reaction occurs, and the resulting solution turns moist red litmus paper blue.

State the equation for the reaction of calcium with cold water.
Give the name for this reaction.
Give 4 observations a student would see when this experiment is carried out.

Answer 4

-Ca(s) + H2O(l) -> Ca(OH)2(aq) + H2(g)
It is a redox reaction (Ca 0 -> +2, H +1 -> 0)
-exothermic reaction (temp of solution increases)
-fizzing/effervescence
-metal dissolves away
-white precipitate may be seen

Question 5

Magnesium burns with a bright white light and is used in flares and fireworks.

Use your knowledge of group 2 metals with water to explain why water should not be used to put out a fire in which magnesium is burning.

Answer 5

• H2 is produced in reaction: M + 2H2O -> M(OH)2 + H2
• H2 is highly flammable, could cause an explosion

Question 6

Reaction of group 2 metals with hot steam.
Give the equation for the reaction of magnesium with steam.

Answer 6

Mg(s) + H2O(g) -> MgO(s) + H2(g)

Question 7

Magnesium reacts readily with steam.

State 2 observations you would make when magnesium reacts with steam.

Answer 7

In presence of steam,
-Mg burns with a bright white flame
-A white powder of MgO is left behind

Question 8

Give the most common allotropes of P, S and Cl.

Using your answer, explain why the melting points follow this trend:

P < S > Cl > Ar

Answer 8

P4, S8, Cl2.

increasing Mr, increasing vdW
S8 has the highest Mr

Question 9

Observations as you put a group 2 metal in water

Question 10

Give the steps of extracting Ti from TiO2. Explain some limitations of the process and why it is expensive.

Answer 10

Start with TiO2
- TiO2(s) + 2Cl2(g) + 2 C(s) -> TiCl4(l) + 2CO(g)
Displacement reaction with Mg under argon at 500 degrees
TiCl4 + Mg2 -> Ti(s) + 2MgCl2(s)

LIMITATIONS
-Mg expensive
-cooling cost, as each batch must be cooled before emptying it, so cooling and heating
-heating cost

Question 11

Applications of group 2 compounds
- milky
- gardens
- barely
- fart gas
- let’s test

Answer 11

• Milk of magnesia suspension of Mg(OH)2 to neutralise excess stomach acid
  Mg(OH)2(s) + 2HCl(aq) -> MgCl2 + 2H2O
• Calcium hydroxide Ca(OH)2 used to neutralise acidic soils, and as a test for carbon dioxide
• Barium sulfate is used as a barium meal for X-ray imaging
• Calcium oxide - used in flue gas desulfurisation to neutralise acidic SO2
• test for hydroxide ions, add soluble salt eg MgCl2