Reactions of the Group 2 Oxides and Hydroxides, and Trends in Solubility

Question 1

what are the group 2 oxides classified as and what does it mean

Answer 1

• basic oxides

- meaning they can react with water to form alkalis

Question 2

what observation is made when a group 2 oxide reacts with water

Answer 2

the solids react to form colourless solutions

Question 3

what is the general equation for the reaction between a group 2 oxide and water using M

Answer 3

MO(s) + H2O(l) = M(OH)2(aq)

Question 4

what is the ionic equation for these reactions and what do they tell us (you can split the oxide into its ions to show this)

Answer 4

• M2 + + O2- + H2O = M2+ + 2OH- (cancel M2+ spectator)
• O2+ + H2O = 2OH-
• the product is hydroxide ions, which is what makes them alkaline

Question 5

what is the trend in the solubility of the group 2 hydroxides down the group

Answer 5

their solubility increases down the group

Question 6

what does this therefore mean about the trend in heir pH down the group

Answer 6

it also increases

Question 7

what is the limewater in the carbon dioxide test

Answer 7

saturated aqueous solution of calcium hydroxide

Question 8

what is the equation for the reaction between limewater and CO2

Answer 8

CO2(g) + Ca(OH)2(aq) = CaCO3(s) + H2O(l)

Question 9

why is magnesium hydroxide often used to relieve symptoms of indigestion

Answer 9

• because its an alkali
• indigestion is often caused by too much HCl in the stomach
• so by taking in Mg(OH)2 it neutralises some of the acid to relieve symptoms

Question 10

what is the equation for the reaction between magnesium hydroxide and hydrochloric acid

Answer 10

Mg(OH)2 + 2HCl = MgCl2 + 2H2O

Question 11

what do all group 2 oxides and hydroxides react with acids to form

Answer 11

salt and water

Question 12

what observations are made from all of these reactions

Answer 12

a white solid reacting to form a colourless solution

Question 13

how lime (calcium hydroxide) used in agriculture

Answer 13

• farmers use it to control soil acidity

- so a greater yield of crops can be obtained

Question 14

are all group 2 nitrates and chlorides soluble

Answer 14

yes

Question 15

what is the trend in the solubility of group 2 sulfates down the group

Answer 15

their solubility decreases

Question 16

therefore why are barium ions used in the test for sulfate ions in solution

Answer 16

• because when barium and sulfate ions react to form barium sulfate
• it would form a white precipitate as it is barely soluble

Question 17

what is the ionic equation for this reaction

Answer 17

Br2+(aq) + SO4^2-(aq) = BrSO4(s)

Question 18

as there are other anions that could form a white precipitate with barium ions, what needs to be added into the solution in order to stop this and how will it do this

Answer 18

• a dilute acid like HCl or HNO3
• these would bring H+ ions into the equation
• this would prevent barium carbonate from forming as a white precipitate
• as the CO3^2- ions would react with the H+ ions to form hydrocarbonate ions (HCO3-)

Question 19

why is barium sulfate used in hospitals for people

Answer 19

• the barium sulfate is put into a meal forming a barium meal
• the BrSO4 allows soft tissues to show up in x-rays clearly for examination
• as its a dense white solid

Question 20

despite barium ions being poisonous, why is barium sulfate used for people

Answer 20

• because barium sulfate is insoluble

- so the ions arent free to move and poison