1. X and Y are FLAMMABLE and should be treated with care
Carbonyls
X and Y are FLAMMABLE and should be treated with care

2. Fehling’s test
Fehling’s reagent is made by mixing equal volumes of a solution containing copper (II) ions complexed with tartrate ions and a solution containing hydroxide ions. What colour is it?
Place about 5cm3 of the Fehling’s solution into a boiling tube and add a few anti-bumping granules.
Test samples X by adding seven drops to the Fehling’s and heating in a water bath until boiling.
Test Y in a similar way.

3. Tollen’s test
Put about 6cm3 of silver nitrate solution in a test tube.
Add ammonia solution slowly until a precipitate of silver (I) oxide forms.
Add more aqueous ammonia until the precipitate just dissolves. You now have Tollen’s reagent – ammoniacal silver nitrate.
Split the solution into two test tubes.
Put 6-7 drops of X in one and 6-7 drops of Y in the other.
Put the test tubes in a hot water bath.
Once the reaction is finished, rinse out the test tubes thoroughly in the fume cupboard before placing in the washing up bowl [the mixture is explosive when dry]

4. Action of acidified potassium dichromate (VI)
Test 5 drops of X and Y each with acidified potassium (or sodium) dichromate (VI) and warm. Use about 2 cm3 of the dichromate (VI) solution – add about an equal volume of 2M sulfuric acid unless it is already acidified! If nothing happens in the cold, warm gently.

5. Explanations
Which ion is responsible for the blue colour in Fehling’s reagent?
Cu2+(aq)
Why are the Cu2+ ions complexed with tartrate ions?
To prevent them precitpitating with hydroxide ions
The red precipitate is copper (I) oxide, Cu2O.
What has happened to the Cu2+ to cause the colour change?
reduced
So what must have happened to Y?
oxidised

6. equations
Half equations: 2Cu2+(aq) + 2OH-(aq) + 2e- Cu2O(s) + H2O(l) RCHO (aq) + 3OH- (aq) RCOO-(aq) + 2H2O(l) + 2e- Overall: RCHO + 2Cu2+ + 5OH- Cu2O + 3H2O + RCOO- Simple chemical equation: RCHO + [O] RCOOH

7. Tollen’s reagent contains diammine silver (I)
[Ag(NH3)2]+(aq)
The silver (I) is reduced to silver giving the metallic silver mirror.
Half equations:
[Ag(NH3)2]+(aq) + e Ag(s) + 2NH3(aq)
RCHO (aq) + 3OH- (aq) RCOO-(aq) + 2H2O(l) + 2e-
Overall:
2[Ag(NH3)2]+ + RCHO + 3OH RCOO- + 2H2O + 2Ag + 4NH3

8. Simple chemical equation:
RCHO + [O] RCOOH

9. The dichromate (VI) ion is orange. It is reduced to chromium (III)
The dichromate (VI) ion is orange. It is reduced to chromium (III). Cr2O72-(aq) + 14H+(aq) + 6e- 2Cr3+(aq) + 7H2O(l) Orange green 3RCHO + 3H2O 3RCOOH + 6H+ + 6e- 3RCHO + Cr2O H+ 3RCOOH + 4H2O(l) + 2Cr3+