CE chemistry

1.
Sulphuric acid is used to acidify the potassium dichromate solution, as acidified potassium dichromate is used as the oxidizing agent of the reaction. (When concentrated sulphuric acid is added to the potassium dichromate solution, the acid is diluted by the water in the potassium dichromate solution and then becomes dilute sulphuric acid.)
3CH3CH2OH + 2K­2Cr2O7 + 8H2SO4 →3CH3COOH + 2K2SO4 + 2Cr2(SO4)3 + 9H2O

2.
Monomers of urea methanal : H2N-CO-NH2 and H-CO-H

Repeated unit of urea methanal : (-HN-CO-NH-CH2-)

Chemical formula of urea methanal: (-HN-CO-NH-CH2-)n

Equation of polymerization to form urea methanal:
n H2N-CO-NH2 + n H-CO-H →(-HN-CO-NH-CH2-)n + (2n - 1)H2O

3.
The set-up of fractional distillation and that of distillation are similar. There is a fractional distillation fitted between the flask and the still head in the set-up of fractional distillation, but there is not in that of distillation.

When is distillation used, and when is fractional distillation used ? The answer depends on what you want to do.

The use of distillation is:
(1) to separate the solvent from the solution (e.g. to separate water from sea water); and
(2) to make the solution of ethanol made from fermentation more concentrated.

The use of fractional distillation is to separate two or more liquids with distinct difference in boiling points.
=

1. conc. sulphuric acid acts as an oxidizing agent.

2. NH2-X-NH2 + HOOC-Y-COOH (dioic acid) or dichloride

where X and Y are hydrocarbon, like CH2-CH2,etc...

this is a condensation reaction

3. they are more or less the same, but fractional distillation is in large- scale...i think...

1...用o來做catalyst 2...其實唔洗識得寫- -"佢唔會問你咁其ge式... 3.distillation靜係可以分開倒兩隻野...仲有佢地ge boiling point至少差大約10度...而fractional就可以分開多好多野...好似fractional distillation of crude oil...分開佢做naptha丫...refinery gar丫...o個d咁...不過都要boiling point有d分別...決定用邊個就多數都係由佢地用o來分幾多隻野而定...