Halogen displacement reactions

Question 1

What can a more reactive halogen do to a less reactive halogen?

Answer 1

displace it from its compounds

Question 2

investigating displacement practical

Answer 2

• adding a halogen solution to a metal halide solution
• see if the mixture darkens, indicating a reaction

-chlorine in ‘chlorine water’ displaces bromine from sodium bromide solution

CL2 + 2NaBr -> 2NaCl + Br2

ionic equation (Na+ ions are spectator ions):

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

Question 3

redox reaction

Answer 3

a reaction in which both oxidation and reduction happens

Question 4

define oxidation and reduction

Answer 4

Oxidation
Is
Loss of electrons

Reduction
Is
Gain of electrons

(OIL RIG)

Question 5

What type of reaction are halogen displacements

Answer 5

redox reactions

e.g.: chlorine displaces bromine from bromide ions in solution

1) chlorine atoms gain electrons and are reduced to chloride ions
2) bromide ions lose electrons and are oxidised to bromine

Question 6

Explain a redox reaction using chlorine and sodium bromide as an example

Answer 6

-chlorine is added to sodium bromide
(Cl2 + NaBr)
-both substances have a neutral charge

-chlorine displaces bromine to make sodium chloride
(Cl2 + NaBr -> NaCl + Br2)
-chlorine and bromine swap places

balanced:
Cl2 + 2NaBr -> 2NaCl + Br2

ionic equation:
-as Na is removed from the equation, the other elements in the compound gain a charge
-the charge is negative because group 7 elements form 1- ions
Cl2 + 2Br- -> 2Cl- + Br2

(the charges are always shown in the upper right of the symbol)

Question 7

How do you write half equations, using chlorine and sodium bromide as an example?

Answer 7

the loss or gain of electrons is always shown by + ne-

the e- represents the charge of the lost/gained electrons
the n is how many are gained or lost

the electrons are never - from the equation

in reduction the electrons are shown on the left side to indicate a gain of electrons:
Cl2 + 2e- -> 2Cl-

in oxidation the electrons are shown on the right to indicate a loss of electrons/the electrons separating from the substance:
2Br- -> Br2 + 2e-

(the substances are balanced as the uncharged atoms exist in pairs)

Question 8

A student adds a few drops of halogen solutions to small volumes of potassium halide solutions on a potting tile.

The three halides and halogens used are chlorine, bromine and iodine

State which potassium halides are displaced by:

a) chlorine
b) bromide
c) iodide

Answer 8

a) bromide and iodide
b) iodide
c) none of them

Question 9

Aqueous bromine solution reacts with aqueous potassium iodide solution

a) write the balanced equation and the ionic equation
b) explain, with the help of half equations, why this reaction is a redox reaction

Answer 9

a) Br2(aq) + 2KI(aq) -> 2KBr(aq) + I2(g)
Br2 + 2I -> 2Br + I2

b) bromide atoms (in Br2) gain electrons and are reduced to bromide ions

Br2 + 2e- -> 2Br-

Iodide ions lose electrons and are oxidised to iodine

2I- -> I2 + 2e-

Question 10

State and explain whether astatine will react with potassium iodide solution

Answer 10

astatine will not react with potassium iodide solution because

• reactivity decreases down group 7
• astatine is less reactive than iodine

Question 11

ionic equation

Answer 11

an equation that includes the charges of the ions

spectator ions can be left out

Question 12

spectator ions

Answer 12

ions that are unchanged (in charge) during a reaction

e.g. Na in the reaction of chlorine with sodium bromide

Question 13

In a redox reaction, what happens to:

a) atoms that gain electrons
b) ions that lose electrons

Answer 13

a) they are reduced to chloride ions
(‘reduced’ because reduction is gain of electrons)

b) they are oxidised to atoms

Question 14

Why are atoms that gain electrons described as ‘reduced’ to ions?

Answer 14

reduction is the gain of electrons