The Halide Salts.Aim: To identify and understand the general

properties of the halide salts.To understand that halide ions are reducing

agents and identify their reactions with concentrated sulphuric acid.

Properties of Halide Salts. Crystalline?

Water soluble?

Conductivity?

Mpt. Bpt?

Bonding?

Formation of Halide Salts. Reaction with group 1 metals. (Sodium

chloride)

Reaction with group 2 metals. (Magnesium chloride)

Reaction with d-block metals.( Copper (II) Chloride)

Halide Ions as Reducing agents. The reaction between (aq) sodium iodide and iron (III)

Chloride to make Iodine, Iron (II) chloride and Sodium chloride

NaI + FeCl3 I2 + FeCl2 + NaCl.

Ionic half equation for Iodine:

Ionic half equation for Iron:

Overall redox equation:

Reducing agent?

Halides as Reducing agents………… What is a reducing agent?

A substance that reduces another species by giving it one or more electrons. It undergoes oxidation as it loses electrons.

What is the trend in power of reducing power of halide ions as group 7 is descended?

I-1>Br-1>Cl-1>F-1 . I-1 loses electrons more

easily than F-1 Why?

Reaction of Halide Salts with Conc. Sulphuric Acid.

Acid + Halide salt can make

Hydrogen halides – HCl, HBr, HI.NaCl + H2SO4 HCl + NaHSO4

These products can go on to react with the sulphuric acid – and

reduce it.

How would we prove that

hydrogen halides are produced in the

reaction?

Hydrogen halides make dense white fumes when they react with conc

ammonia solution.

What is the equation for this type of reaction?

NH3+ HCl NH4Cl

Reaction of Hydrogen Halides with Conc Sulphuric acid.

Possible products when hydrogen halides react

with Conc sulphuric include sulphur dioxide, Hydrogen Sulphide and

the Halogen itself.

How do you test for Sulphur

dioxide?

Acidified potassium dichromate paper turns form orange to green

if sulphur dioxide is present.(Reaction type?)

How do you test for

Hydrogen Sulphide?

It smells of rotten eggs!

How do you identify the halogens?

Chlorine – Bleaches damp blue litmus

paper.Bromine – Slowly as above + distinctive

colour.Iodine – Distinctive

colour

Reaction of Halides with Sulphuric Acid.Halide Observation

with conc Sulphuric acid

Confirmatory test

Inference

KCl

KBr

KI.

Reaction of Halides with Sulphuric Acid.Halide Observation

with conc Sulphuric acid

Confirmatory test

Inference

KCl Steamy fumes in cold, no apparent effect when

heated

White smoke with ammonia - HCl, damp litmus paper turns red (not bleached) – no Cl2

HCl

KBr Steamy fumes in cold, brown gas on warming

(Br2)

White smoke with ammonia HBr.

acidified potassium dichromate(VI) goes from orange to green

– SO2 .

HBr & Br2, & SO2

KI. Steamy violet fumes in cold, more on warming (I2), bad egg smell (H2S)

White smoke with ammonia – HI

acidified potassium dichromate(VI) goes from orange to green – SO2

HI, I2 & H2S & SO2

Reaction with KCl KCl + H2SO4 HCl + KHSO4

What are the oxidation numbers of each element in each compound on the reactant side?

K = Cl= H= O= S=

Oxidation numbers on the product side? Is the Chloride ion acting as a reducing agent?

Reaction of KBr and Sulphuric Acid.

Reaction with KBr. Step 1 – Production of HBr. KBr + H2SO4 Step 2 – Reaction of HBr + H2SO4 HBr + H2SO4

What is the change in oxidation number of Bromide in the reaction?

Has the Bromide ion been oxidised or reduced? What is the change in oxidation number of

Sulphur during the reaction? Has Sulphur been oxidised or reduced? Is the Bromide ion a reducing or oxidising agent?

Br2 + SO2 + H2O

Reaction with KI 2KI(s) + H2SO4(l) KHSO4(s) + 2HI(g)

2HI(g) + H2SO4(l) SO2(g) + 2H2O(l) + I2(s)

AND 8HI(g) + H2SO4(l) H2S(g) + 4H2O(l) + 4I2(s)

Change in oxidation number of I-1? Change in oxidation number of S? Using these facts why is I-1 a stronger reducing

agent compared to Br-1?

Questions What halides have reduced the Sulphuric

acid? From your observations put the hydrogen

halides in order of reducing ability – most to the least.

How did you come to this conclusion? Explain why the hydrogen halide you have

chosen is the best reducing agent.

Homework Write up the halide ion tests in your lab

book from last week. See p.154 AS chemistry.

P156 AS chemistry Questions 1,2,3,4,6,7,10 –Only.

For Thursday.