Reactions of Halide ions | Quizlet

In terms of redox, what happens to halide ions in a reaction?

-The halide ions are oxidised to form halogen molecules

2X⁻ → X₂ +2e⁻

-Halide ions go from -1 to 0, so they act as oxidising agents

What is the trend in reducing ability down Group 7 (halogens)? Explain why.

-Trend: Increases down the group (F⁻ is the weakest reducing agent, I⁻ is the strongest).

Reason:

-Atomic radius increases → Outer electrons are less attracted to the nucleus.

-Easier to lose electrons (oxidize) → Halide ions (X⁻) donate electrons more readily down the group.

What is the reaction between bromide ions and concentrated sulfuric acid?

-H₂SO₄ (l) + NaBr (s) → HBr (g) + NaHSO₄ (s)

The concentrated sulfuric acid oxidises HBr which decomposes into bromine and hydrogen gas and sulfuric acid itself is reduced to sulfur dioxide gas:

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

What is observed in this reaction?

-Misty fumes of SO₂ gas

-Orange-brown bromine vapor (Br₂).

-Pungent sulfur dioxide gas (SO₂).

What is the general method for testing for halide ions in solution?

-Add dilute nitric acid to remove interfering ions (e.g., carbonate).

-Add silver nitrate solution (AgNO₃).

-Observe the precipitate formed.

-Confirm by adding dilute ammonia (NH₃) or concentrated ammonia.

What colour precipitate does chloride ion (Cl⁻) form with silver nitrate?

-White precipitate (AgCl).

What colour precipitate does bromide ion (Br⁻) form with silver nitrate?

-Cream precipitate (AgBr).

What colour precipitate does iodide ion (I⁻) form with silver nitrate?

-Yellow precipitate (AgI).

What happens when chloride ions (Cl⁻) react with concentrated H₂SO₄?

Observations: Steamy white fumes (HCl gas).

NaCl+H₂SO4₄→NaHSO₄​+HCl

Type of reaction: Acid-base (HCl is not oxidized further).

What happens when bromide ions (Br⁻) react with concentrated H₂SO₄?

Observations:

Steamy white fumes (HBr gas).

Orange-brown bromine vapor (Br₂).

Pungent sulfur dioxide gas (SO₂).

-NaBr +H₂​SO₄→NaHSO₄+HBr (reaction 1)

-the concentrated sulfuric acid then oxidises the HBr, which decomposes into bromine and hydrogen gas and sulfuric acid then reduced to sulphur dioxide

-2HBr+H₂​SO₄​→Br₂+SO₂​+2H₂​O

What happens when iodide ions (I⁻) react with concentrated H₂SO₄?(observations)

-Steamy white fumes (HI gas).

-Purple iodine vapor (I₂).

-Rotten egg smell (H₂S gas).

-Yellow solid sulfur (S).

What are the 4 reactions and the formulas when iodide ions(I⁻) react with concentrated H₂SO₄?

-H₂SO₄ (l) + NaI (s) → HI (g) + NaHSO₄ (s)

-Since the HI molecule readily decomposes, what is formed when sulfuric acid oxidises the HI? What is observed?

-2HI(g) + H₂SO₄(l) → I₂(g) + SO₂ (g) + 2H₂O (l)

-Iodine gas emits purple vapours

-sulfuric acid reduced to sulfur dioxide

-What are the other products formed when HI is readily decomposed with sulfuric acid? What is observed in each reaction?

6HI (g) + H₂SO₄ (l) → 3I₂ (g) + S (s) + 4H₂O (l)

-sulfuric acid reduced to sulfur

-Yellow solid of D

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

-sulfuric acid reduced to hydrogen sulfide

-H₂S smells of bad eggs

What toxic gases are produced when I⁻ reacts with H₂SO₄?

-Hydrogen sulfide (H₂S) - rotten egg smell.

-Sulfur dioxide (SO₂) - choking, pungent gas.

What is the trend in thermal stability of hydrogen halides (HX) down Group 7, and why does this occur?

Trend: Thermal stability decreases down the group.

-due to bond strength decreasing as the atomic radius is larger

-and bond enthalpy decreases