Topic 4

Question 1

How do you test for carbonate or hydrogencarbonate ions? CO3-2orHCO3-1

Answer 1

Add HCl, a positive result shows fizzing due to production of CO2 gas. Test for gas using limewater. It turns cloudy in the presence of CO2.

Question 2

What is limewaters chemical composition?

Answer 2

Calcium hydroxide solution

Question 3

What is the test for SO4-2

Answer 3

Add dilute HCl to remove any traces of carbonate ions then add BaCl2. A positive results shows the formation of a white precipitate.

Question 4

How to test for ammonium ions. NH4+

Answer 4

Add some NaOH and gently heat. Test the neck of the tube with damp litmus paper. It’s damp so that the ammonia gas can dissolve. Positive result shows a colour change from red litmus paper to blue.

Question 5

How to test for Cl- ions.

Answer 5

Bleaches damp blue litmus paper. It turns red then blue.

Question 6

What colours are group one metal ion flames?

Answer 6

Li - red
Na - orange/yellow
K - lilac
Rb - red
Cs - blue

Question 7

What colours are the group 2 metal ion flames?

Answer 7

Ca - brick red
Sr - crimson
Ba - green
Pb - grey flame
Cu - blue/green

Question 8

What are the two chemical tests for water?

Answer 8

Add anhydrous CuSO4 (white) which becomes CuSO4.5H2O (blue) in the presence of water

Or

Add anhydrous CoCl2 (blue) which becomes CoCl2.6H2O (pink) in the presence of water.

Question 9

What is the physical test for pure water?

Answer 9

Heat to boiling, use a thermometer to measure the temperature at which it boils. If it’s at 100*C, it’s pure.

Question 10

What is the test for ethanol.

Answer 10

Put a lighted splint near it and if it ignites, it’s ethanol. It also has an antiseptic smell.

Question 11

What is the test for ethanoic acid?

Answer 11

Colourless liquid which smells like vinegar.

Question 12

How to test for halide ions?

Answer 12

Add dilute HNO3 to remove any extra ions and add AgNO3 to make a precipitate.
Cl- —> white precipitate dissolved in dilute ammonia solution
Br- —> cream precipitate dissolved in concentrated ammonia solution
I- —> yellow precipitate doesn’t dissolve in any sort of ammonia

Question 13

How do group 1 carbonates decompose?

Answer 13

Only LiCO3 decomposes into Li2O and CO2.

Question 14

How do group 1 nitrates decompose?

Answer 14

XNO3 —> XNO2 + O2

Except Li: LiNO3 —> Li2O + NO2 + O2

Question 15

How do group 2 carbonates decompose?

Answer 15

XCO3 —> XO + CO2

Question 16

How do group 2 nitrates decompose?

Answer 16

X(NO3)2 —> XO + NO2 + O2

Question 17

Write the reaction of chlorine with cold water for water treatment.

Answer 17

Cl2 + H2O —> ClO- + Cl- + H+

Question 18

Write the reaction for chlorine with cold NaOH

Answer 18

Cl2 + NaOH —> NaClO + NaCl + H2O

Question 19

Write the reaction for chlorine with hot NaOH

Answer 19

Cl2 + NaOH —> NaClO3 + NaCl + H2O

Question 20

Does the reducing power of a halide increase or decrease down a group?

Answer 20

Increases down the group because there is less attraction between the electrons and the nucleus.

Question 21

What happens when a hydrogen halide dissolved in water?

Answer 21

HX + H2O —> H3O+ + Cl-

Question 22

What happens when a hydrogen halide reacts with ammonia

Answer 22

NH3 + HX —> NH4X

Question 23

What happens when KF or KCl reacts with H2SO4?

Answer 23

KF + H2SO4 —> KHSO4 + HF.
HF produces misery fumes upon contact with moisture in the air.

Question 24

What happens when KBr reacts with H2SO4.

Answer 24

KBr + H2SO4 —> KHSO4 + HBr.

HBr has misery fumes

HBr + H2SO4 —> Br2 + SO2 + H2O

Question 25

What happens when KI reacts with H2SO4?

Answer 25

KI + H2SO4 —> KHSO4 + HI
HI + H2SO4 —> I2 + SO2 + H2O
HI + SO2 —> H2S + I2 + H2O
H2S is toxic and smells bad