GROUP 7

Question 1

What is the trend in the boiling point down group 7? why? (4)

Answer 1

Increases down the group
size of atoms increases
increase in number of electron so
stronger van der waals forces of attraction between molecules require more energy to overcome

Question 2

What is the trend in electronegativity down group 7? Why? (5)

Answer 2

Decreases
increased atomic radius
more shielding
outer e- further away from nucleus
more difficult yo attract electron density in a covalent bond

Question 3

state and explain trend in oxidising ability in group 7

Answer 3

going down G7 halogens become weaker oxidising agents.
Larger radius
Weaker attraction between nucleus and outer e-

Question 4

Describe what you would see if you combined the following reagents and write stoichiometric and ionic equations for any reactions that take place

1. Br2 (aq) with NaF (aq)
2. Cl2 (aq) with NaBr (aq)
3. Br2 (aq) with NaI (aq)

Answer 4

1. No reaction occurs, Bromine can’t displace fluoride
2. An orange- brown solution forms
   Cl2(aq) + 2NaBr(aq) –> 2NaCl(aq) + Br2(aq)

Cl2(aq) + 2Br-(aq) –> 2Cl-(aq) + Br2(aq)

3. Orange solution turns brown
   Br2(aq) + 2NaI(aq) –> 2NaBr(aq) + I2(aq)

Br2(aq) + 2I-(aq) –> 2Br-(aq) +I2(aq)

Question 5

State and explain the trend in reducing ability of the halide ions

Answer 5

Reducing strength increases down group
ions radius increases
Weaker attraction between outer e- and nucleus

Question 6

Identify 2 solid sodium halides that can’t reduce concentrated sulphuric acid. write simplest ionic equations for a reaction occurring with just on for a reaction occurring with just one of theses halides and give oberservations

Answer 6

H+ + F- –> HF
Ob: misty fumes of HF gas
H+ + Cl- –> HCl
Ob: misty fumes of HCl gas

Question 7

state the observation you would make if either of NaCl or NaF was reacted with concentrated sulphuric acids

Answer 7

steamy white fumes

Question 8

Name the products formed when solid NaBr reacts with concentrated H2SO4 and state the observations you would make upon their function

Answer 8

Steamy fumes of HBr
brown fumes of Br2
colourless fum of SO2 gas
colourless solution of NAHSO4

Question 9

Write redox equations for the formation of Br with H2SO4

Answer 9

2Br –> Br2 + 2e-
H2O4 + SH+ + 2e- –> SO2 + 2H2O
H2SO4 + 2H+ + 2Br- —> SO2 + 2H2O + Br2

Question 10

Give a common use of Sodium hypochlorite (NaClO)

Answer 10

used as disinfectant as it kills bacteria

Question 11

Write and equation for the reaction between Chlorine and cold dilute sodium hydroxide

Answer 11

Cl2(g) + 2NaOh(aq) —-> NaCl(aq) + NaClO(aq) + H2O(l)

Question 12

Even though chlorine is toxic , why do we add it to swimming pools? (2)

Answer 12

adding chlorine to swimming pools kills bacteria.
health benefits of adding very small amount if Cl to water outweigh the risks

Question 13

write equation for the reaction between H2O and Cl in the presence of direct sunlight

Answer 13

2Cl2(g)+ 2H2O (l) (EQUALIBRIUM SIGN) 4HCl (aq) + O2(g)

Question 14

What does disproportination reaction mean?

Answer 14

reaction in which one reactant species is simultaneously oxidised and reduced

Question 15

write the equation for the reaction between water and chlorine to form 2 chlorine- containing products

Answer 15

Cl2(g) + H2O(l) (EQUILIBRIUM ARROW) HCL(aq) + HCLO(aq)

Question 16

test for carbonate ions

Answer 16

Add H2SO4
effeservence
Co2 produced

Question 17

<write a half equation for the formation of Iodine from Iodide ions

Answer 17

2I- —-> I2 + 2e-

Question 18

Test for hydroxide ions

Answer 18

MgCl2
White ppt
Mg(OH)2 formed

Question 19

Test for ammonium ions

Answer 19

add NaOH
warm it
gas turns dam red litmus paper blue it indicates ammonium ions were present

Question 20

ionic equation for NaBr and silver nitrate

Answer 20

Ag+ (aq) + Br-(aq) —-> AgBr(s)

Question 21

why is the silver nitrate test used to identify used to identify halide ions

Answer 21

produces precipitate that are easily identified by colour

Question 22

Fluoride reaction with ammonia
colour of precipitate

Answer 22

No reaction
no colour

Question 23

Chloride reaction with ammonia
colour of precipitate

Answer 23

colour: white ppt
reaction: Dissolve in dilute ammonia

Question 24

Bromide reaction with ammonia
colour of precipitate

Answer 24

colour: Cream ppt
reaction: Dissolve in concentrated ammonia

Question 25

Iodide reaction with ammonia
colour of precipitate

Answer 25

colour: yellow ppt
reaction: insoluble in concentrated ammonia

Question 26

why is dilute nitric acid added before the silver nitrate for a halide test

Answer 26

to remove soluble carbonate and hydroxide ions would give a false +ve result

Question 27

describe how you would carry out the halide test

Answer 27

1. Dissolve sample in water
2. Add HNO3
3. Add AgNO3 solution
4. Change in colour
5. Add dilute NH3
6. Add conventrayed NH3

Question 28

write half equations for the formation of the 3 sulfur-contacting reduction products of this reaction

Answer 28

H2SO4 + 2H+ + 2e- –> SO2 + 2H2O

H2SO4 + 6H+ + 6e- —> S + 4H2O

H2SO4 + 8H+ + 8I- —> H2S + 4H2O

Question 29

write a redox equations for the formation of the 3 sulphur- containing reductions products of this reaction

Answer 29

H2SO4 + 2H+ + 2I- —> SO2 + 2H2O + I2

H2SO4 + 6H+ + 6I- —-> S + 4H2O + 3I2

H2SO4 + 8H+ + 8I- —> H2S + 4H2O + 4I2

Question 30

Name the products formed when solid NaI reacts with concentrated sulphuric acid and state the observations you would make upon their formation

Answer 30

steamy fumes of HI
black solid of I2
Bad eggs smell caused by H2S
yellow solid of S
colourless solution of NaHSO4

Question 31

Write equation for the precipitates

Answer 31

Ag+ + I- ——> AgI
Ag+ + Br- ——> AgBr
Ag+ + Cl- ——> AgCl

Question 32

Equation for NH3 with
AgCl
AgBr

Answer 32

AgCl + 2NH3 ——> Ag(NH3)2 +Cl-
AgBr + 2NH3 ——> Ag(NH3)2 +Br-

Question 33

Cl is often added to water because it….

Answer 33

Sterelises wate4 by killing bacteria