3.2.3 - Group 7, the Halogens

Question 1

Why does electronegativity and reactivity decrease down group 7? (3)

Answer 1

• Atoms get larger
• More distance between nucleus and electrons (ionic radius increase)
• Weaker attraction to pair of electrons in covalent bond

Question 2

Halogen displacement principle

Answer 2

A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt

Question 3

Test for halides

Answer 3

Add dilute nitric acid and then silver nitrate solution.

Question 4

White ppt in test for halides

Answer 4

Chloride ions

Question 5

Cream ppt in test for halides

Answer 5

Bromide ions

Question 6

Yellow ppt in test for halides

Answer 6

Iodide ions

Question 7

Purpose of nitric acid while testing for halides

Answer 7

Reacts with any anions (e.g. carbonates) which would give false positive

Question 8

What is the solubility in ammonia of Cl,Br,I ?

Answer 8

Cl- dissolves in dilute NH3
Br- dissolves in conc NH3
I- is insoluble in NH3

Question 9

Test for ammonium compounds

Answer 9

Add NaOH, gently heat
Damp red litmus paper will turn blue in presence of ammonia gas

Question 10

Test for hydroxides

Answer 10

Red litmus paper turns blue

Question 11

Test for carbonates

Answer 11

Add dilute HCl
Bubble gas through limewater, will turn cloudy

Question 12

Test for sulfates

Answer 12

Add HCl + barium chloride
White precipitate will form

Question 13

Chloride + conc sulfuric acid product

Answer 13

White gas

Question 14

Bromide + conc sulfuric acid product

Answer 14

Orange gas

Question 15

Iodide + conc sulfuric acid produces a…

Answer 15

Purple gas

Question 16

Why does BaCl2 need to be acidified?

Answer 16

Both sulfites and sulfates produce a white precipitate with BaCl, acid prevents that.

Question 17

What order should you test group 7 compounds?

Answer 17

Carbonate test - sulfate test - halide test

Question 18

Bleach disproportionation reaction equation

Answer 18

2NaOH + Cl2 —-> NaCl + NaOCl + H2O

Question 19

Why is the bleach reaction a disproportionation reaction?

Answer 19

Chlorine is both reduced and oxidised simultaneously

Question 20

What do iodide ions reduce concentrated sulphuric acid into? (3)

Answer 20

Sulphur dioxide - SO2 (+4)
Sulfur - S (0)
Hydrogen sulfide (H2S) (-2)

Question 21

How do you formulate the half equation for the reduction of sulphuric acid producing … ?

Answer 21

SO4(2-) —– ____ + H20
Balance hydrogens, then charge using e-

Question 22

Water + Cl2 equation

Answer 22

CL2 + H20 —-> HCl + HOCl

Question 23

Overall ionic reaction for reduction with sulphuric acid

Answer 23

H2SO4 + (hydrogens) + (Halide ions) = (reduction product) + (Br2/Cl2/I2) + H20

Question 24

Sodium chloride + conc sulfuric acid equation + role of chloride

Answer 24

NaCl + H2SO4 —-> NaHSO4 + HCL
Act as base (proton accepter)

Question 25

What should you do before testing compounds with silver nitrate?

Answer 25

Add acid, add water, then add silver nitrate.