3.1.3 group 7

Question 1

describe the properties of the first 4 halogens

Answer 1

F2 pale yellow gas
Cl2 greenish gas
Br2 red liquid
I2 shiny grey solid

Question 2

state and explain the trend of melting points down the halogens

Answer 2

increases
•molecules become larger
•more electrons so more attraction to nucleus
•stronger london forces between molecules so more energy needed to overcome

Question 3

state and explain the trend of electronegativity down the halogens

Answer 3

decrease
•shielding increases as there are more shells
•electrons in the covalent bond are further from nucleus so attraction decreases to the nucleus

Question 4

give the basic equation of a halogen acting as an oxidising agent

Answer 4

X2(?) + 2e- —> 2X-(aq)

Question 5

state and explain the trend of oxidising power down the halogens

Answer 5

decrease
•shielding increases as shells increase
•electrons are further away from nucleus so less attraction
•so less likely to gain an electron

Question 6

give the basic equation of a halide acting as a reducing agent

Answer 6

2X-(aq) —> X2(?) + 2e-

Question 7

state and explain the trend of reducing power down the halides

Answer 7

increases
•number of shells in the ions increases so shielding increases
•less attraction of outer electrons to nucleus so they are more easily lose

Question 8

give an equation and state the observations of Cl2 reacting with
KBr

Answer 8

colourless —> yellow solution

2KBr(aq) + Cl2(aq) —> 2KCl(aq) + Br2(aq)

Question 9

give an equation and state the observations of Cl2 reacting with
KI

Answer 9

colourless —> brown solution

2KI(aq) + Cl2(aq) —> 2KCl(aq) + I2(aq)

Question 10

give an equation and state the observations of Br2 reacting with
KI

Answer 10

colourless —> brown solution

2KI(aq) + Br2(aq) —> 2KBr(aq) + I2(aq)

Question 11

what are the changes in displacement reactions of halogens if an organic solvent is added

Answer 11

Cl - colourless
Br -yellow
I -purple

Question 12

give the method of reacting halide ions with AgNO3

Answer 12

1) make solution of halide
2) acidity with dilute nitric acid to prevent formation of insoluble silver salts
3) add AgNO3 solution
4) if ppt is formed add dilute NH3
5) if still ppt add concentrated NH3

Question 13

give the colour ppt that is formed when cl, br and i react with AgNO3

Answer 13

AgCl white
AgBr cream
AgI yellow

Question 14

how can you tell the difference between AgCl AgBr and AgI

Answer 14

AgCl dissolves in dilute ammonia whereas AgBr and AgI do not

AgBr dissolves in concentrated ammonia whereas AgI does not

Question 15

define disproportionation

Answer 15

when an element is simultaneously oxidised and reduced

Question 16

define electronegativity

Answer 16

the relative tendency of an atom in a covalent bone in a molecule to attract electrons in a covalent bond to itself

Question 17

give the reaction of chlorine with water and give the colour change when indicator is added

Answer 17

Cl2(g) + H2O(l) —> HClO(aq) + HCl(aq)

will first turn red then colourless as HClO bleaches the colour

Question 18

give the equation of Cl with NaOH and give the colour change

Answer 18

Cl2(aq) + 2NaOH(aq) —> NaCl(aq) + NaClO(aq) + H2O(l)

colourless

Question 19

what is a use of NaClO

Answer 19

bleach to kill bacteria