Chemical Tests

Question 1

which flame colour does sodium give

Answer 1

yellows

Question 2

which flame colour does potassium give

Answer 2

lilac

Question 3

which flame colour does calcium give

Answer 3

yellow-red/ red-orange

Question 4

which flame colour does barium give

Answer 4

pale green

Question 5

which flame colour does lithium give

Answer 5

red

Question 6

which flame colour does strontium give

Answer 6

crimson

Question 7

which flame colour does rubidium give

Answer 7

red-violet

Question 8

which flame colour does caesium give

Answer 8

blue

Question 9

which flame colour does magnesium give

Answer 9

no colour

Question 10

Describe the 2 tests used to identify Group 2 ions

Answer 10

1. Adding sodium hydroxide solution, NaOH(aq), to produce a group 2 hydroxide
2. Adding sulfuric acid, H2SO4(aq) or sodium sulphate solution, Na2SO4(aq), to make a group 2 sulphate
   - The solubility of the precipitates formed will help to identify the ions

Question 11

describe the observation of adding Mg+2 to sodium hydroxide solution.
State how soluble the hydroxide produced is

Answer 11

• a thick white precipitate of magnesium hydroxide is formed
• the magnesium hydroxide is not soluble

Question 12

describe the observation of adding Ca+2 to sodium hydroxide solution.
State how soluble the hydroxide produced is

Answer 12

• a white precipitate of calcium hydroxide is formed
• the calcium hydroxide is not very soluble

Question 13

describe the observation of adding Sr+2 to sodium hydroxide solution.
State how soluble the hydroxide produced is

Answer 13

• a thin white precipitate of strontium hydroxide is formed
• the strontium hydroxide is soluble

Question 14

describe the observation of adding Ba+2 to sodium hydroxide solution.
State how soluble the hydroxide produced is

Answer 14

• a very thin white precipitate of barium hydroxide is formed
• the barium hydroxide is very soluble

Question 15

Write an ionic equation for the reaction between a group 2 metal ion (M) with sodium hydroxide

Answer 15

M2+(aq) + OH-(aq) -> M(OH)2(s)

Question 16

describe the observation of adding Mg+2 to sodium sulphate solution.
State how soluble the sulphate produced is

Answer 16

• no precipitate is formed
• the magnesium sulphate is very soluble

Question 17

describe the observation of adding Ca+2 to calcium sulphate solution.
State how soluble the sulphate produced is

Answer 17

• a thin white precipitate is formed
• the calcium sulphate is soluble

Question 18

describe the observation of adding Sr+2 to sodium sulphate solution.
State how soluble the hydroxide produced is

Answer 18

• a white precipitate is formed
• the strontium sulphate is not very soluble

Question 19

describe the observation of adding Ba+2 to sodium sulphate solution.
State how soluble the hydroxide produced is

Answer 19

• a thick white precipitate is formed
• the barium sulphate is not soluble

Question 20

Write an ionic equation for the reaction between a group 2 metal ion (M) with sodium sulphate

Answer 20

M+2(aq) + SO4-2(aq) -> MSO4(s)

Question 21

describe the test for ammonium ions, NH4 +

Answer 21

1. Place a few cm^3 of sodium hydroxide solution in a test tube and add a spatula measure of the sample, warm gently.
2. Test any gas evolved using damp red litmus paper or damp universal indicator paper or using a glass rod dipped in concentrated hydrochloric acid
   - Observation: if ammonium ions are present: a pungent gas is released, indicator paper turns blue, white smoke with glass rod
   - Detail of reaction: when the ammonia compound reacts with the sodium hydroxide solution, ammonia gas is produced (alkaline). White smoke is ammonium chloride from the reaction between ammonia and hydrogen chloride

Question 22

Write an ionic equation for the reaction between ammonium ions and the sodium hydroxide solution

Answer 22

NH4 +(aq) + OH-(aq) -> NH3(g) + H20(l)

Question 23

describe the test for halide ions, Cl-, Br- and I-

Answer 23

1. Dissolve a spatula measure of the sample in dilute nitric acid and add a few cm^3 of silver nitrate solution.
2. Add dilute/ concentrated ammonia solution
   Observation:
   - if chloride ions present, a white precipitate (AfCl) is redissolved in dilute ammonia solution to form a colourless solution
   - if bromide ions present, a cream precipitate (AgBr) is NOT redissolved in dilute ammonia solution, but is redissolved in the concentrated ammonia solution to form a colourless solution
   - If iodine ions present, a yellow precipitate (AgI) is NOT redissolved in neither dilute ammonia solution or concentrated ammonia solution
   - if no halide ions present, no precipitate is formed

Question 24

Write the ionic equation for the reaction between acidified silver nitrate solution and a halide ion (X)

Answer 24

Ag+(aq) + X-(aq) -> AgX(s)

Question 25

Describe the test for sulphate ions, SO4 -2

Answer 25

1. Dissolve a spatula measure of the sample in dilute nitric acid (or hydrochloric acid) and add a few cm^3 of barium chloride solution Observations: - if sulphate ions present, white precipitate (BaSO4) is formed - if no sulphate ions present, no precipitate is formed

Question 26

Describe the test for carbonate ions, CO3 -2, or hydrogen carbonate ions, HCO3 -

Answer 26

1. Place a few cm^3 of dilute nitric acid in a test tube and add a spatula measure of the sample Observations: - if carbonate ions or hydrogen carbonate ions present, there's fizzing and gas is produced. This gas can be passed through limewater in another test tube. If the limewater changes from colourless to milky, CO2 is present - if no carbonate ions or hydrogen carbonate ions present, there's no gas produced or fizzing