CPAC 4

Question 1

what test do we use for magnesium ions( Mg2+)

Answer 1

We have to add a solution, which has hydroxide ions, and this forms magnesium hydroxide.

A white precipitate will form.

This is because solubility decreases as we go down group 2.

Question 2

What test do we use for ammonium ions?

Answer 2

We place 10 drops of ammounium chloride solution into a test tube.

We then add an equal volume of dilute sodium hydroxide solution, stir the mixture, and warm gently in a water bath.

add damp red litmus paper, in the test tube.

RESULTS: Litmus paper should turn blue.

EXPLENATION: ammonium and hydroxide ions, react to produce ammonia gas.
-NH4+ + OH- —-> NH3+H2O.

ammonia is an alkali, which means it turns dam red litmus paper, into blue.

Question 3

How do we test for hydroxide ions?

Answer 3

method: dip universal indicator into solution.

results: It will turn from red to blue

Question 4

How do we test for carbonate ions?

Answer 4

place carbonate ions, into a test tube. connect VIA delivery tube, another test tube , containing calcium hydroxide solution ( limewater).

We then add dilute hydrochloric acid to the test tube containing the carbonate ions

RESULTS: The The sodium carbonate solution bubbles, and the colourless calcium hydroxide solution, turns cloudy.

EXPLENATION: Carbonate ions react with acid, in order to form carbon dioxide gas, this is responsible for the bubbling.

-CO3(2-)+ 2H+ —->CO2+2H2O

then carbon dioxide, reacts with the calcium hydroxide solution, and forms calcium carbonate. This is insoluble in water, so forms a white precipitate, that makes the solution cloudy.

-Ca(OH)2+CO2 —->CaCO3+ H2O.