testing for cations and anions - RP

Question 1

how do you test for group 2 metals

Answer 1

-add 10 drops of 0.1mol dm-3 barium chloride solution should be added to the first test tube
-around 10 drops of dilute NaOH solution to the same test tube
-swirl the test tube carefully to mix
-continue to add the sodium hydroxide solution dropwise until in excess
-repeat for calcium bromide solution, magnesium chloride solution and strontium chloride solution

Question 2

results for testing for Mg2+ ions

Answer 2

ammonium solution:
white precipitate - Mg(OH)2

Excess sodium hydroxide solution:
white precipitate - Mg(OH)2

Excess sulfuric acid:
colourless solution

Question 3

results for testing for Ca2+ ions

Answer 3

ammonium solution:
no change seen

Excess sodium hydroxide solution:
white precipitate - Ca(OH)2

Excess sulfuric acid:
light white precipitate - CaSO4

Question 4

results for testing for Sr2+ ions

Answer 4

ammonium solution:
no change seen

Excess sodium hydroxide solution:
slight white precipitate - Sr(OH)2

Excess sulfuric acid:
white precipitate - SrSO4

Question 5

results for testing for Ba2+ ions

Answer 5

ammonium solution:
no change seen

Excess sodium hydroxide solution:
no change seen

Excess sulfuric acid:
white precipitate - BaSO4

Question 6

how do you test for ammonium ions and results

Answer 6

-10 drops of solution containing ammonium ions, such as ammonium chloride, added to the clean test tube
-about 10 drops of sodium hydroxide should be added using a pipette
-swirl the test tube to ensure it is mixed well
-the test the solution should then be placed in a beaker of water, and the beaker of water should be placed above a Bunsen burner, so it can become a water bath
-as solution is heated gently, fumes will be produced
-a pair of tongs should be used to hold a damp piece of red litmus paper near the mouth of the test tube, to test the fumes
-the red litmus paper will change colour and become blue in the presence of ammonium gas

Question 7

test for ammonium ions

Answer 7

-10 drops of solution containing ammonium ions, such as ammonium chloride, added to the clean test tube
-about 10 drops of sodium hydroxide should be added using a pipette
-swirl the test tube to ensure it is mixed well
-the test the solution should then be placed in a beaker of water, and the beaker of water should be placed above a Bunsen burner, so it can become a water bath

Question 8

results for test for an ammonium ions

Answer 8

-as solution is heated gently, fumes will be produced
-a pair of tongs should be used to hold a damp piece of red litmus paper near the mouth of the test tube, to test the fumes
-the red litmus paper will change colour and become blue in the presence of ammonium gas

Question 9

how do you test for halide ions

Answer 9

-add sample to test tube using a pipette
-add dilute nitric acid and then silver nitrate solution

Question 10

results for testing for halide ions

Answer 10

-chloride ions form white precipitate of AgCl
-bromide ions form a cream precipitate of AgBr
-iodide ions form a yellow precipitate of AgI

Question 11

results for further test of halide ions

Answer 11

-AgCl forms soluble complex with dilute ammonia –> dissolves and colour change to colourless
-AgBr forms soluble complex with concentrated ammonia –> dissolves an colour change to colourless
-AgI doesn’t form a soluble complex with ammonia so remains as yellow precipitate

Question 12

test for hydroxide ions

Answer 12

-small amount of solution should be added to the test tube using a pipette
-test the pH using red litmus paper or universal indicator indicator paper

Question 13

results for the test for the hydroxide ions

Answer 13

-presence of hydroxide ions will turns red litmus paper blue and the pH will clearly be alkaline on the universal indicator indicator paper of hydroxide ions are present

Question 14

test for carbonate ions

Answer 14

-add a small amount of dilute HCL to test tube using a pipette
-an equal amount of sodium carbonate solution should then be added to the test tube using a clean pipette
-as soon as sodium carbonate solution is added, a bung with a delivery tube should be attached to test tubes
-the delivery tube should transfer the gas which is formed into a different test tube contains a small amount of limewater (calcium hydroxide solution)

Question 15

results for testing for carbonate ions

Answer 15

-carbonate ions react with hydrogen ions form the acid to produce carbon dioxide gas
-the carbon dioxide gas will turn the limewater milky

Question 16

how do you test for sulfate ions

Answer 16

-acidify the sample with dilute hydrochloric acid then add a few drops of aqueous barium chloride

Question 17

results for test for sulfate ions

Answer 17

is sulphate ions is present then a white precipitate of barium sulphate is formed
equation:
Ba2+ (aq) + SO42- (aq) → BaSO4 (s)

Question 18

test for chloride ion as a solid salt

Answer 18

concentrated sulfuric acid:
white, steamy fumes

Blue litmus:
turns red

Question 19

test for bromide ions as a solid salt

Answer 19

concentrated sulfuric acid:
orange fumes

Blue litmus:
turns red

Question 20

test for iodide ions as a solid salt

Answer 20

concentrated sulfuric acid:
purple fumes and purple/black solid

Blue litmus:
turns red