Unit 2: Section 2 - Reactions of halide ions

The oxidation states of the sulfuric acid with hydrogen bromide is first +6, it then decreases to...

+4 (red.)

The oxidation states of the hydrogen bromide with sulfuric acid is first -1, it then increases to...

0 (ox.)

How do you test for Halide ions?

1) First you add dilute nitric acid to remove ions which might interfere with the test. 2) Add a few drops of silver nitrate solution (AgNO₃(aq)). 3) A precipitate of the silver halide is formed

What is produced when solid sodium iodide reacts with concentrated sulphuric acid?

1) Steamy fumes of HI 2) Black, I₂ 3) Pungent smell of H₂S gas is present 4) Yellow solid MAY be seen 5) Colourless SO₂ (choking)

What are the products when Sodium bromide reacts with sulfuric acid?

1) Steamy fumes of hydrogen bromide 2) Orange fumes of bromine 3) Colourless, choking sulfur dioxide

Why does the reducing ability of halide ions increases down the group?

1) the ions get bigger, so the electrons are further away from the positive nucleus 2) there are extra inner electron shells, so there's a greater shielding effect.

Give the equations of the 2 step reaction of NaBr with H₂SO₄

1. NaBr(s) + H₂SO₄(aq) → NaHSO₄(s) + HBr(g) 2. 2HBr(aq) + H₂SO₄(aq) → Br₂(g) + SO₂(g) + 2H₂O(l) The HBr is a stronger reducing agent than HCl and reacts with the H₂SO₄ in a redox reaction.

What is produced when sulfuric acid reacts with Sodium bromide?

1st: NaHSO₄²⁻ and HBr 2nd: SO₂, Br₂ and H₂O

What is the second balanced symbol equation between sodium bromide and sulfuric acid?

2HBr(aq) + H₂SO₄(aq) → Br₂(g) + SO₂(g) + 2H₂O(l)

What is the second balanced symbol equation between hydrogen iodide and hydrogen sulphate?

2HI(g) + H₂SO₄(aq) → I₂(s) + SO₂(g) + 2H₂O(l) Oxidation states of hydrogen sulphate is the same as in the other reaction between sodium bromide and hydrogen sulphate!

The third balanced symbol equation between hydrogen iodide and sulphur dioxide is...

6HI(g) + SO₂(g) → H₂S(g) + 3I₂(s) + 2H₂O(l)

How can you test for sulfates with HCl and Barium Chloride?

Add a little dilute HCl acid, followed by barium chloride solution, BaCl₂ (aq). Ba⁺(aq) + SO₄²⁻ (aq) → BaSO₄ If a white precipitate of barium sulfate forms, it means the original compound contained a sulfate!

To be extra sure of your results after having done the initial test for halide ions, what could you do?

Add ammonia solution! Each silver halide has a different solubility in ammonia! Chloride: white precipitate, dissolves in dilute NH₃(aq) Bromide: cream precipitate, dissolves in dilute NH₃(aq) Iodide: yellow precipitate, insoluble in conc NH₃(aq)

Use Red Litmus Paper and NaOH to test for...

Ammonium Ions! 1) Ammonia gas (NH₃) is alkaline - so you can test for it using a damp piece of red litmus paper. If ammonia is present, the paper will turn blue! 2) If you add hydroxide ions (OH⁻) to a solution containing ammonium ions (NH₄⁺), they will react to produce ammonia gas and water: NH₄⁺(aq) + OH⁻(aq) → NH₃(g) + H₂O (l) 3) Add some dilute sodium hydroxide solution to your substance in a test tube and gently heat the mixture. If there's ammonia given off, ammonium ions must be present.

Describe how a student could distinguish between aqueous solutions of potassium nitrate, KNO₃, and potassium sulfate, K₂SO₄, using one simple test-tube reaction.

BaCl₂ KNO₃: Colourless solution K₂SO₄: White precipitate

If you did not use nitric acid to neutralise the solution when trying to identify the halide ions present. The precipitate formed would be...

Brown-Silver Oxide

What does Br₂ look like?

Br₂ looks like orange fumes when produced in the reaction between NaBr and H₂SO₄

The symbol of nitric acid is...

HNO₃

_____________ ________ can be used to help detect carbonates.

Hydrochloric acid When you add dilute HCl acid, a solution containing carbonate ions will fizz. This is because the carbonate ions react with H ions in the acid to give CO₂. Limewater can be used to test for CO₂, turning the limewater cloudy!

What would you use to test for Hydroxides?

Hydroxide ions make solutions alkaline. So if you think a solution might contain hydroxide ions, you can use a pH indicator to test it. E.g. 1) Dip a piece of red litmus paper into the solution! 2) If hydroxide ions are present, the paper will turn blue!

Explain the trend in reducing power of the Halides!

It increases down the group! 1) the ions get bigger, so the electrons are further away from the positive nucleus! 2) there are extra inner electron shells, so there's a greater shielding effect!

Why isn't hydrochloric acid used to acidify the solution when testing for halide ions?

It would give a precipitate of silver chloride. Which would also invalidate the test.

When testing for halides, why is sulfuric acid not used to acidify the solution?

It would give a precipitate of silver sulfate. Which would invalidate the test.

Why does HBr react with the sulfuric acid in the second reaction?

It's a stronger reducing agent than HCl and reacts with the H2SO4 in a redox reaction.

What type of reaction is the reaction between Solid sodium bromide and concentrated sulphuric acid?

Its a redox reaction! The reactions are exothermic and some of the bromine vaporises.

For all of the halide ion reactions (in a compound with sodium) with concentrated sulphuric acid, the first reaction is as follows...

Na'X' + H₂SO₄ → NaHSO₄ + H'X'

What's the symbol equation for the reaction between sodium chloride and sulfuric acid?

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

Describe how a student could distinguish between aqueous solutions of magnesium chloride, MgCl₂, and aluminium chloride, AlCl₃, using one simple test-tube reaction.

NaOH MgCl₂: White precipitate AlCl₃: White precipitate dissolves in excess NaOH

Give the reagent you would use to distinguish between NaF(aq) and NaCl(aq) and what you'd observe.

Silver nitrate NaF(aq): no observable change NaCl(aq): white precipitate

Why must the litmus paper be damp when testing for ammonia gas?

So the ammonia can dissolve

Sodium chloride and and Sodium fluoride react with sulfuric acid react to produce...

Steamy fumes of hydrogen chloride, or Steamy fumes of hydrogen fluoride. In either case, the solid product is sodium hydrogen sulfate.

When sodium bromide reacts with sulfuric acid there are 2 reactions. True or False?

TRUE

Suggest why iodide ions are stronger reducing agents than chloride ions.

The atomic radi of iodide ions are larger than those of chloride ions. This means that there is increased shielding, increasing the reducing ability.

What test would you use to identify group 2 ions?

The flame test! Compounds of some group 2 metals burn with characteristic colours. 1) Dip a nichrome wire loop in concentrated HCl. 2) Dip the wire loop into the unknown compound. 3) Hold the loop in the blue flame of a Bunsen burner. 4) Observe the colour change in the flame.

When testing for halide ions, give the trend in of fastest to slowest forming precipitate.

The precipitate forms faster down the group!

Why, when identifying metal halides with silver ions, is dilute nitric acid added to the halide solution?

To get rid of any soluble carbonate or hydroxide impurities. These would intefere with the test by forming insoluble silver carbonate/hydroxide.

The colours of silver bromide and silver iodide are similar but if you add a few drops of concentrated ________________, silver bromide dissolves but silver iodide does not.

ammonia solution

What flame colour does Calcium produce?

brick red

In concetrated aqueous ammonia X will dissolve. What is X?

bromine

What colour are bromine fumes?

brown

Sulfur dioxide is...

colourless and a choking gas!

What colour precipitate do bromide ions form?

cream

A precipitate of chlorine ions will dissolve in...

dilute aqueous ammonia

After acidifying the solution, a few drops of silver nitrate are added to...

identify any halide ions!

What type of reaction is the reaction between Sodium Chloride and sulfuric acid?

its an acid-base reaction

What does the oxidation state of 6HI and sulphur dioxide change to in the third reaction of sodium iodide?

ox. state of S: ⁺4 goes to ⁻2 ox.state of I₂: ⁻1 goes to 0

What flame colour does Barium produce?

pale green

What is the colour of the precipitate formed by iodide ions?

pale yellow

What flame colour does Strontium produce?

red

All metal halides react with ________________ in aq solution, e.g. in silver nitrate, to form a precipitate of the insoluble silver halide.

silver ions (Ag³⁺)

What colour precipitate do chloride ions form?

white