Group 7 QA FA

Question 1

All halogens are…

Answer 1

Non-metals

Brittle and crumbly when solid

Question 2

Colour and standard state of fluorine

Answer 2

Pale yellow gas

Question 3

Colour and standard state of chlorine

Answer 3

Yellow/green gas

Question 4

Colour and standard state of bromine

Answer 4

Red/brown liquid

Question 5

Colour and standard state of iodine

Answer 5

Grey solid

Question 6

Trend in melting and boiling points down the group and an explanation

Answer 6

Increase going down the group

Due to the stronger VDW’S forces due to increasing atomic radius

Question 7

General half equation for halogens forming a halide

Answer 7

X2+2e-→2X-

Question 8

Which halogen is the best oxidising agent and why?

Answer 8

Fluorine
Least shielding and smallest distance
Despite low nuclear charge
So, strongest attraction between nucleus and new electrons
Accepts electrons the easiest

Question 9

Displacement reactions occur if…

Answer 9

The most reactive species is not starting in a compound

If there’s enough activation energy

Question 10

In a displacement reaction, what is the oxidising agent and what is the reducing agent?

Answer 10

Oxidising agent: halogen

Reducing agent: halide

Question 11

Which halide is the strongest reducing agent and why?

Answer 11

Iodide
Largest atomic radius, so most shielding
Least attraction to the outer electron
Easier to lose outer electrons

Question 12

How does NaF react with concentrated sulphuric acid?

Answer 12

Fluoride is not a good reducing agent, so an acid-base reactions takes place

NaF(s)+H2SO4(l)→NaHSO4(aq)+HF(g)

(steamy fumes of HF)

Question 13

How does NaCl react with concentrated sulphuric acid?

Answer 13

NaCl(s)+H2SO4(l)→NaHSO4+HCl

steamy fumes of HCl

Question 14

How does NaBr react with concentrated sulphuric acid?

Answer 14

Step 1: NaBr(s)+H2SO4(l)→NaHSO4(aq)+HBr(g)
(steamy fumes of HBr)

Step 2: 2HBr+H2SO4→Br2+SO2+2H2O

Question 15

How does NaI react with concentrated sulphuric acid?

Answer 15

Step 1: NaI(s)+H2SO4(l)→NaHSO4(aq)+HI(g)
(stemy fumes of HI)

Step 2: 8HI+H2SO4→4I2+H2S+4H2O

Question 16

What do you observe when NaCl reacts with concentrated sulphuric acid?

Answer 16

Colourless gas (HCl) or white fumes evolved

Question 17

What do you observe when NaBr reacts with concentrated sulphuric acid?

Answer 17

Colourless gas (HBr) or white fumes evolved
SO2 gas given off
Dark orange vapour (Br2)

Question 18

What do you observe when NaI reacts with concentrated sulphuric acid?

Answer 18

Colourless gas (HI) or white fumes evolved
SO2 and H2S gases given off
Violet vapour/black solid (I2)

Question 19

What is the test for halides?

Answer 19

Add nitric acid, then silver nitrate solution

Question 20

Why is nitric acid added to the substance first when testing for halides?

Answer 20

To prevent a false positive result

Question 21

What will you observe depending on the halide when testing for halides?

Answer 21

Fluoride - no precipitate
Chloride - white precipitate
Bromide - cream precipitate
Iodide - yellow precipitate

Question 22

What is used to check the halide test and why?

Answer 22

Ammonia
Silver chloride redissolves in any ammonia solution
Silver bromide redissolves in concentrated ammonia solution
Silver iodine will not redissolve in any ammonia solution