(1) Group 2 & Group 7

Question 1

Explain the trend in electronegativity moving down group 7.

Answer 1

• Increasing atomic radius
• Decreasing attraction between nucleus and outer electron
• Electronegativity decreases

Question 2

Explain why fluorine is the weakest reducing agent, whereas Iodine is a very good reducing agent.

Answer 2

• Iodide has a larger atomic radius and more shielding
• Weaker nuclear attraction between nucleus and outer electron
• so its more willing to give up additional electron making it a good reducing agent.

Question 3

Write an equation for the reaction of concentrated sulfuric acid with solid sodium fluoride and state observations.

Answer 3

H2SO4 + NaF → NaHSO4 + HF

-solid formed and steamy fumes of HF gas is released

Question 4

Suggest one reason why the reaction of sodium fluoride with concentrated sulfuric acid is different from the reaction with sodium iodide.

Answer 4

Fluoride less powerful reducing agent than iodide.

may not react as well as iodide

Question 5

Write an equation for the reaction of concentrated sulfuric acid with solid sodium chloride and state observations.

What is the role of the Cl- ions?

Answer 5

NaCl(s) + H2SO4(aq) → NaHSO4(s) + HCl(g)

• solid formed and steamy fumes of HCL gas is released
• proton acceptor (accepts H+ to form HCl)

Question 6

Write an equation for the reaction of concentrated sulfuric acid with solid sodium bromide then with bromide ions and state observations.

Answer 6

NaBr(s) + H2SO4(aq) → NaHSO4(s) + HBr(g)

2H+ + H2SO4 + 2Br- → SO2 + 2H2O + Br2

• acidic gas forms and brown fumes of bromine gas appear

Question 7

Sodium bromide reacts with concentrated sulfuric acid in a different way from sodium chloride. Explain why bromide ions react differently from chloride ions.

Answer 7

• > Br- ions are bigger than Cl- ions
• > weaker nuclear attraction between nucleus and outer electron
• > Therefore Br- ions lose an electron more easily than Cl- ions

Question 8

What three things iodide ions can reduce Sulphur in H2SO4 down to?

Answer 8

• SO2 (g)
• S (s)
• H2S (g)

Question 9

Write an equation for the reaction of concentrated sulfuric acid with solid sodium iodide (initial reaction).

Answer 9

NaI(s) + H2SO4(aq) → NaHSO4(s) + HI(g)

Question 10

Write an equation for the reaction of concentrated sulfuric acid with iodide ions to form SO2 and state observations.

Answer 10

2H+ + H2SO4 + 2I- → SO2 + 2H2O + I2

• acidic SO2 gas forms and a black solid of Iodine forms

Question 11

Write an equation for the reaction of concentrated sulfuric acid with iodide ions to form S and state observations.

Answer 11

6H+ + H2SO4 + 6I- → S + 4H2O + 3I2

• yellow solid sulfur produced and black solid of Iodine forms

Question 12

Write an equation for the reaction of concentrated sulfuric acid with iodide ions to form H2S and state observations

Answer 12

8H+ + H2SO4 + 8I- → H2S + 4H2O + 4I2

• gas smelling of bad eggs and black solid of Iodine forms.

Question 13

What is the test for halide ions

Answer 13

• Add dilute nitric acid (HNO3) to remove any carbonate ions which may alter results
• then silver nitrate solution (AgNO3)
• observe

Question 14

Describe the observations following a Halide Ions test.

Answer 14

F- : clear colourless solution

Cl- : white precipitate

Br- : cream precipitate

I- : yellow precipitate

Question 15

What can be done to the precipitates to confirm the halide ions test?

Answer 15

Ammonia can be added.

Question 16

Describe the observations after adding Ammonia to Halide Ions.

Answer 16

• The COLOURLESS solution for fluoride ions will show no visible change as there’s no precipitate
• The WHITE precipitate for chloride ions will dissolve in dilute ammonia.
• The CREAM precipitate for bromide ions wont dissolve in dilute ammonia, but will dissolve in concentrated ammonia.
• The YELLOW precipitate for iodide ions is completely insoluble even in concentrated ammonia.

Question 17

What are the uses of Chlorine?

Answer 17

• disinfectant for swimming pools and drinking water
• kills bacteria
• manufacture of bleach

Question 18

Give two reasons why chlorine is used for the treatment of drinking water even though the gas is very toxic.

Answer 18

• only used in low concentrations

- the benefits outweigh the risks

Question 19

.Chlorine reacts with water to form an equilibrium mixture containing hydrochloric acid and chloric(I) acid. Write an equation for the formation of this equilibrium mixture.

Answer 19

Cl2(g) + H2O(l) ⇌ HCl (aq) + HClO(aq)

Question 20

State and explain why it is dangerous to acidify an aqueous mixture of sodium chlorate(I) and sodium chloride.

Answer 20

Equilibrium shifts and moves left

Producing chlorine gas which is toxic.

Question 21

What’s a disproportionation reaction?

Answer 21

A reaction where the same element is oxidised and reduced in the same reaction.

Question 22

State the equation which occurs to cause the chlorine concentration to decrease.

Answer 22

2Cl2(g) + 2H2O(l) → 4HCl(aq) + O2(g)

Question 23

Give the equation of the disproportionation reaction which forms a chlorine compound found in bleach.

Answer 23

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

Question 24

Give the equation for the reversible reaction sodium chlorate or calcium chlorate is added to water.

Answer 24

NaClO(s) + H2O(l) → Na+(aq) + -OH(aq) + HClO(aq

Question 25

Describe the boiling points of halogens.

Answer 25

• non-polar molecules
• meaning they have induced dipole dipole attractions
• The strength of these is dependent on the size of the molecule,
• F2 has the lowest melting point and boiling point, I2 has the highest melting point and boiling point