Inorganic 1 - halogens

How do the halogens vary in appearance?

Fluorine is a pale yellow gas, chlorine is a pale green gas, bromine is red-brown liquid, iodine is a black solid - they get darker and denser going down.

What happens to atomic radius going down group 7?

It increases because each element has one extra energy level compared to the one above it

How does electronegativity change going down Group 7?

Decreases as the atomic radius increases and shielding from the electron shells, and although number of protons increases the shielding outweighs it, so attraction of nucleus to electron bonding pair decreases.

What happens to melting and boiling point going down group 7?

Increases going down the group, because larger atoms have more electrons and this makes the van der Waals forces between molecules stronger, and the ones with lower melting point are more volatile

What happens to the oxidising ability of the halogens going down the group?

Decreases going down the group, because as you go down the nuclear attraction of outer electrons to the outer shell decreases due to increased shielding which outweighs increased nuclear charge. So Fluorine has the greatest ability to accept electrons.

How do halogens react with metal halides?

In such a way that the halide in the compound will be displaced if the halogen is more reactive but not if it is less reactive - called a displacement reaction.

What can halide ions act as?

Reducing agents (electron donors)

What happens to the reducing ability of halide ions as you go down the group?

As you go down the group, they become more powerful reducing agents because electron is lost more easily from the outer shell - it is further from the nucleus and there is more shielding.

Do F- and Cl- undergo redox reactions?

They are not powerful enough, so when reacting with concentrated H2SO4 only an acid base reaction occurs.

Do Br- and I- undergo redox reactions?

Yes, they undergo both acid-base and redox reactions

What are the observations when F- is added to HSO4?

White misty fumes due to HF being produced in acid-base reaction

What are the observations when Cl- is added to HSO4?

White misty fumes due to HCl being produced in acid-base reaction

What happens when Br- reacts with H2SO4 in the redox reaction, and what would be observed?

It is only powerful enough to convert H2SO4 (+6) to SO2 (+4). Orange-brown fumes of Bromine produced would be seen, and colourless sulfur dioxide is produced in the redox reaction. This is an exothermic reaction.

What happens when Br- reacts with H2SO4 in the acid-base reaction, and what would be observed?

Bromine would act as a base and accepts H+ ions, which produces HBr (misty fumes), and this also produces sodium hydrogensulfate.

Give the overall reaction for the redox reaction of Br- with H2SO4:

2H+ + 2Br- + H2SO4 → SO2 + 2H2O + Br2

What happens in redox reaction with I- and H2SO4, and what observations would be made?

I- is a powerful enough reducing agent to convert H2SO4 to SO2, S (0) and H2S (-2). You would see the purple vapour of I2, the rotten egg smell of H2S, and the yellow solid sulfur in different reactions.

During the reduction from +6 to -2 what would be observed?

Sulfur passes through oxidation state 0, so solid yellow sulfur may be seen.

Give the equation for the acid base reaction that occurs with I-:

NaI + H2SO4 → NaHSO4 + HI

Give the equation for the reaction of I- and H2SO4 to give H2S:

8H+ + H2SO4 +8I-- → H2S + 4H2O +4I2

Give the equation for the reaction of I- and H2SO4 to give S:

6H+ + H2SO4 + 6I- → S + 4H2O + 3I2

Explain the test for halide ions?

All metal halides (except fluorides) react with siliver ions in aqueous solution to produce a precipitate of the insoluble silver halide. Silver fluoride is soluble in water.

• Dilute nitric acid is first added to halide solution to remove soluble carbonate ions or hydroxide impurities, as if these are present they also form precipitates

• Then a few drops of silver nitrate are added and precipitate will form.

• Ammonia is added as a further test

Observations of the halide test?

• Chloride forms a white precipitate, and dissolves in dilute ammonia

• Bromide forms a cream precipitate, and dissolves in concentrated ammonia

• Iodide forms a pale yellow precipitate, and does not dissolve in concentrated ammonia

How does chlorine react with water?

In a reversible reaction to form chloric (I) acid, HClO and HCl.

What are the oxidation states of the chlorine atoms in the reaction with water?

One atom decreases from 0 to -1 and the other increases from 0 to +1

What is a disproportionation reaction?

When a single chemical species is simultaneously oxidised and reduced forming 2 species with different oxidation states.

What is the reaction between chlorine and water used for?

Used to purify water and swimming baths to prevent diseases.

What is chloric acid used for

Is an oxidising agent and kills bacteria by oxidation, and is a b

What is the reaction of chlorine and water in sunlight?

2Cl2 (g) + 2H20 (l) → 4HCl (aq) + O2 (g) - chlorine is easily lost from pool water so needs frequent addition of chlorine

What is an alternative to the direct chlorination of pool water?

Add sodium/calcium chlorate (I). Dissolves in water to to produce chloric acid

What is the equation for the reaction between water and sodium chlorate?

NaClO + H20 →←Na + + OH- + HClO

Why are swimming pools kept slightly acidic?

Because in alkaline solution equilibrium moves to the left and HClO is removed as ClO- ions, this is monitored so the metal components don't corrodd

What does it produce when chlorine reacts with cold, dilute NaOH?

Sodium chlorate

What does sodium chlorate act as and what is its role in everyday life?

Oxidising agent, is the active ingredient in bleach

What is the equation for the reaction between chlorine and NaOH?

Cl2 + 2NaOH → NaClO + NaCl + H20 is a disproportionation reaction because one Cl atom gets reduced and one gets oxidised.

What are the tests for group 2 ions?

• Add 10 drops of sodium hydroxide to sample of group 2 ions and swirl to mix.

• Continue adding dropwise until in excess, this should be repeated for other test tubes.

• Group 2 ions will produce a white precipitate (apart from Ba2+)

How to test for ammonium ions?

• Add 10 drops of sodium hydroxide using a pipette, and swirl carefully

• Place in a beaker of hot water from a kettle, and fumes will be produced.

• Hold a damp piece of red litmus paper near the mouth, and this will become blue in the presence of ammonia gas.

How to test for hydroxide ions?

• Add the sample being tested with a pipette, then test the pH using universal indicator paper. pH will be clearly alkaline on the paper if these ions are present

How to test for carbonate ions?

• Add the sample into a test tube, then add 10 drops of hydrochloric acid and immediately fit with a delivery tube into a half a test tube full of limewater, if the ions are present the limewater turns cloudy

How to test for sulfate ions?

• Acidify the sample with HCl and add a few drops of barium chloride.

• If sulfate is present a white precipitate of barium sulfate is formed