halogens

Question 1

appearance of flourine

Answer 1

pale yellow gas

Question 2

appearance of chlorine

Answer 2

green gas

Question 3

appearance of bromine

Answer 3

red-brown liquid

Question 4

appearance of iodine

Answer 4

grey solid

Question 5

what colour will the solution go if bromine is displaced

Answer 5

yellow

Question 6

what colour will the solution go if iodine is displaced

Answer 6

orange / brown

Question 7

fluoride + sulfuric acid
+ observation

Answer 7

NaF (s) + H2SO4 (aq) = NaHSO4 (aq) + HF (g)
Misty white fumes (HF)

Question 8

chloride + sulfuric acid

Answer 8

NaCl (s) + H2SO4 (aq) = NaHSO4 (aq) + HCl (g)
Misty white fumes (HCL)

Question 9

bromide + sulfuric acid

Answer 9

NaBr (s) + H2SO4 (aq) = NaHSO4 (aq) + HBr (g)
Misty white fumes (HBr)

2HBr (g) + H2SO4 (aq) = Br2 (g) + SO2 (g) + 2H2O (l)
Orange vapour (Br2)

Question 10

iodide + sulfuric acid

Answer 10

NaI (s) + H2SO4 (aq) = NaHSO4 (aq) + HI (g)
Misty fumes

2HI (g) + H2SO4 (aq) = I2 (g) + SO2 (g) + 2H2O (l)
Violet iodine vapour (I2)

6HI (g) + SO2 (g) = H2S (g) + 3I2 (s) + 2H2O (l)
Violet iodine vapour (I2)
Rotten egg smell (H2S)

Question 11

Testing for halide ions method + findings

Answer 11

• add dilute nitric acid to remove any impurities like carbonates
• add silver nitrate solution
• observe precipitate colour

Chloride = white
Bromide = cream
Iodide = yellow

Question 12

confirming identity of halide ions (not using silver nitrate)

Answer 12

add excess ammonia

chloride = dissolves in both conc and dilute
bromide = dissolves in conc, not dilute
iodide = doesn’t dissolve in conc or dilute

Question 13

using chlorine to disinfect drinking water

Answer 13

Cl2 (g) + H2O (l) = HCl (aq) + HClO

HCLO dissociates:
HClO = H+ (aq) + ClO-
The ClO- ions act as a disinfectant.

In sunlight-
Cl2 (g) + 2H2O (l) = 2HCl (aq) + 1/2 O2 (g)

Question 14

making bleach

Answer 14

Cl2(g) + 2NaOH (aq) = NaClO (aq) + NaCl (aq) + H2O (l)

cold, dilute sodium hydroxide

Question 15

identifying carbonate ions

Answer 15

• add dilute nitric acid (HNO3) dropwise
• observe for effervescence (CO2)

CO3 2- (aq) + 2H+ (aq) = CO2 (g) + H2O (l)

Confirm presence of CO2 by bubbling through limewater, if it turns cloudy, CO2 is present

CO2 (g) + Ca(OH)2 (aq) = CaCO3 (s) + H2O (l)

Question 16

identifying sulfate ions

Answer 16

• add dilute nitric acid dropwise
• add a few drops of a solution containing aqueous Ba 2+ ions (like BaCl2 or Ba(NO3)2 )
• observe for white precipitate of BaSO4
• Ba 2+ (aq) + SO4 2- (aq) = BaSO4 (s)