Group 7

Question 1

Does boiling point increase down the group? Why?

Answer 1

Yes
Increasing strength of VdW forces as size and relative mass increases so more energy is required to overcome these.

Question 2

Does electronegativity increase down the group? Why?

Answer 2

No.
Larger atoms attract electrons less than smaller one since atomic radius and shielding is larger. Leading to reduced attraction.

Question 3

Does halogen oxidising power decrease down the group? Why?

Answer 3

Yes
Larger atoms with more shielding make it easier to gain an electron due to reduced attraction to the nucleus so it is harder to gain an electron.

Question 4

What is a halide?

Answer 4

A negative ion of a halogen.

Question 5

Which halides does chlorine displace and what is the ionic equation?

Answer 5

Br- and I-

Br: Cl2 + 2Br- –> 2Cl- + Br2
Orange (Br) solution

I: Cl2 + 2I- –> 2Cl- + I2
Brown (I) solution

Question 6

Properties of fluorine

Answer 6

Pale, yellow gas

Question 7

Properties of chlorine

Answer 7

Pale, green gas

Question 8

Properties of bromine

Answer 8

brown - orange liquid

Question 9

Properties of iodine

Answer 9

grey solid

Question 10

Does reactivity decrease down the group? Why?

Answer 10

Yes
Atoms with a smaller atomic radius find it easier to attract an electron.

Question 11

Which halides does bromine displace and what is the ionic equation?

Answer 11

I-

Br2 + 2I- –> 2Br- + I2
Brown (I) solution

Question 12

Which halides does iodine displace and what is the ionic equation?

Answer 12

Nothing

Question 13

Does halide reducing power decrease down the group? Why?

Answer 13

No
Halide ions need to loose electrons to reduce something which become easier with weaker attraction from larger atomic radius and shielding.

Question 14

What is the silver nitrate test for halides?

Answer 14

Add dilute nitric acid to remove any ions that could interfere.

Add a few drops of silver nitrate solution as it will form different precipitate colours:
Ag+ + X- –> AgX

Add ammonia solution to further separate them as they each have different solubility.

Question 15

In the silver nitrate test, what precipitate colours do each halide produce?

Answer 15

F - None
Cl - White
Br - Cream
I - Yellow

Cl forms slowest
I forms fastest

Question 16

In the silver nitrate test, what are the different solubilitise in ammonia?

Answer 16

Cl - white ppe, dissolve in dilute NH3

Br - cream ppe, dissolves in conc NH3

I - yellow ppe, insoluble in conc NH3

Question 17

What is the reaction of NaCl and sulphuric acid?

Answer 17

NaCl + H2SO4 –> NaHSO4 + HCl

Cl not strong enough to reduce H2SO4 so stops.
Not a redox.

Question 18

What is the reaction of NaBr and sulphuric acid?

Answer 18

2NaBr + H2SO4 –> SO2 + Br2 + 2H20 + Na2SO4

HBr is a strong enough reducing agent to reduce H2SO4.

Redox reaction in the second.

Question 19

What is the reaction of NaI and sulphuric acid?

Answer 19

NaI + H2SO4 –> NaHSO4 + HI

2HI + H2SO4 –> I2 + SO2 + 2H20

6HI + SO2 –> H2S + 3I2 + H2O

HI is a very strong reducing agent so can reduce H2SO4 and further to reduce SO2 and H2S>.

Redox reaction.

Question 20

What reaction creates bleach?

Answer 20

Mixing sodium hydroxide and chlorine to form sodium chlorate(I) solution - bleach.

2NaOH + Cl2 –> NaClO + NaCl + H2O

Question 21

Is the bleach reaction disproportionate?

Answer 21

Yes as chlorine is both reduced and oxidised.

Question 22

Uses of bleach

Answer 22

Treating water, bleaching paper and fabrics, cleaning agents

Question 23

Why does chlorine do in water?

Answer 23

Kill bacteria

Question 24

How does adding chlorine to water kill bacteria? (Include reaction)

Answer 24

H2O + Cl2 –> 2H+ + Cl- + ClO-

ClO- (chlorate ions) kills bacteria.

Question 25

Does adding chlorine to water result in a disproportionate reaction?

Answer 25

Yes as the chlorine is both reduced and oxidised.

Question 26

How does sunlight decompose chlorinated water?

Answer 26

2H2O + Cl2 --> 4H+ + 2Cl- + O2

Question 27

Why does the sunlight decomposed water a problem?

Answer 27

As it contains no chlorate ions which sterilises water.

Question 28

Advantages of chlorinated drinking water

Answer 28

Destroy disease causing microorganisms Long lasting so reduces bacteria down the water supply Reduces growth of bad smelling and testing algae. Prevents cholera epidemics.

Question 29

Disadvantages of chlorinated drinking water

Answer 29

Chlorine gas can irritate the respiratory system .Liquid chlorine can cause chemical burns. Speculation chlorine can react with organic compounds in water to make chloroalkanes which are linked to causing cancer.

Question 30

How do you test for ammonia?

Answer 30

Damp red litmus paper into an area of gas while will turn blue with ammonia gas present.

Question 31

How to test for ammonium atoms? (NH4+)

Answer 31

Add sodium hydroxide and gently heat. If ammonium compound is present, ammonia gas will be released: NH4+ + OH- --> NH3 + H2O Use damp red litmus paper to check again.

Question 32

How to test for sulfates?

Answer 32

Add dilutes HCl Add barium chloride solution: Ba2+ + SO42- --> BaSO4 If a white ppe forms, sulfates present

Question 33

How to test for hydroxides?

Answer 33

Dip red litmus paper into solution. Will turn blue if present.

Question 34

How to test for carbonates?

Answer 34

Add HCl Solution will fizz if CO2 is present due to the carbonate ions: CO32- + 2H+ --> CO2 + H2O