(2.44-2.50) Chemical Tests

Describe a test for hydrogen gas.

Place a lit splint over a test tube of trapped gas. There should be a squeaky pop.

Describe a test for oxygen gas.

Place a glowing splint over a test tube of trapped gas. The splint should relight.

Describe a test for carbon dioxide gas.

Bubble the gas through limewater. It should have bubbles and turn cloudy.

Describe a test for ammonium.

Damp red litmus paper over heated substance and sodium hydroxide solution. Paper should turn blue.

(this is turning ammonium into ammonia gas, then testing)

Describe a test for chlorine gas.

Place damp blue litmus paper over solution. The paper turns red, then white.

How do you carry out a flame test?

Nichrome of platinum wire is dipped in acid to clean it.

Dip the wire in a compound.

Burn the substance in a non-luminous flame and note colour.

Li+, Lithium Colour in flame test

Red

Na+, Sodium Colour in flame test

Yellow

K+, Potassium Colour in flame test

Lilac

Ca2+, Calcium Colour in flame test

Red-Orange

Cu2+, Copper Colour in flame test

Blue-Green

What is the test for Cu2+, Fe2+ and Fe3+?

Sodium hydroxide solution

Test for Cu2+

Add sodium hydroxide solution: Blue precipitate

Test for Fe2+

Add sodium hydroxide solution: Green precipitate

Test for Fe3+

Add sodium hydroxide solution: Brown precipitate

What is the test for these anions: Cl-, Br-, I-?

Use nitric acid and silver nitrate solution.

Test for Cl-

Nitric acid

Silver nitrate solution

result: White

Test for Br-

Nitric acid

Silver nitrate solution

result: Cream

Test for I-

Nitric acid

Silver nitrate solution

result: Yellow

Test for SO42-, Sulfate

Acidified Barium Chloride Solution

result: White precipitate

Test for CO32-. Carbonate

add dilute HCl- bubbles = carbon dioxide

Bubble the gas collected through limewater

to check the bubbles are CO2

result: bubbles and cloudy limewater

How do you test for presence of water?

Add substance to anhydrous copper (||) sulfate

result: White turns Blue

What is a physical test to show whether a sample of water is pure?

Check whether it freezes at 0 degrees and boils at 100 degrees