chemistry paper 3 specimen

Question 1

conc sulphuric acid role in reaction ester and ethanol

Answer 1

acts as a catalyst

Question 2

reflux set up

Answer 2

-water in at bottom and out at top this needs to be done so the water fully fills the condenser and flows properly
-there should not be a bung as it causes a build up of pressure needs to be open top
-there should be clamps
-

Question 3

why is sodium carbonate added to a distillate and why is there a build up of pressure

Answer 3

sodium carbonate reacts with acid to neutralise an acid and it produces CO2 gas which causes a build of pressure

Question 4

in the seperating funnel two layers form the top layer is an ester

Answer 4

ethyl ethanoate is insoluble in water so it forms a separate layer. it forms the upper layer as it has a lower density

Question 5

role of adding anhydrous calcium chloride

Answer 5

it acts as a drying agent to remove/absorb water

Question 6

what hyrdolyses amino acids

Answer 6

HCL in reflux/heat

Question 7

describe what happens when a mixture is heated under reflux and hwy is it necessary for the complete oxidation of something

Answer 7

A mixture of liquids is heated to boiling for a prolonged time. Vapour is formed and escapes the mixture the condenser changes it back into liquid and its returned back to the mixture. so anything that initially is oxidised can be returned back and oxidised.

Question 8

how would you get a sample of something with a lower boiling point and reduce loss of the substance

Answer 8

-heat mixture with a still head containing a thermometer
-have a water cooled condenser connected to a still head and have a suitable cooled collecting vessel (this will minimise the loss of the substance). you will collect the sample at the boiling point of what ur trying to obtain.

Question 9

how to do a KC calculation where you don’t know the moles at equilibrium but you do know how much acid reacts with a base

Answer 9

1. find the moles of the base it reacted with and that’s the same as the moles of acid in a certain volume
2. then multiply up to find the moles in the volume you have
3. moles of acid reacted = moles of ester formed
4. ester moles is used to find the other reactant at equilibrium (ice table)
5. put in to KC equation (volumes often cancel out)

Question 10

in a titration how do you reduce percentage error

Answer 10

without changing what’s in ur burette, you would lower the conc of the base its reacting with so a larger titre is needed this reduced percentage error

Question 11

outline the steps to locate positions of amino acid on TLC plate

Answer 11

-spray with developing agent (often ninhydrin)
-then do rf value

Question 12

positive inductive effect

Answer 12

pushing electron density away from its self electron releasing effect. making it less polar

Question 13

negative inductive effect

Answer 13

withdraws the electron density eg. electronegative groups or double bond O. This makes the molecule more electronegative

Question 14

what does something being more electronegative mean for its acid

Answer 14

more electronegative means its more like to loose H+ making it a stronger acid. acid dissociation of H+ ions determined its strength.

Question 15

ethanedioic acid has what ions … (and what do they turn into in half equation

Answer 15

C2O4 2- (dioate ions)
to
CO2

Question 16

manganate ions and what do they reduce to

Answer 16

MnO4 -
to
Mn2+

Question 17

if going through a mass spectrometer what does it have to be

Answer 17

it has to be a positive ion !!!!!!

Question 18

how does TOF mass spectrometer separate two species to give two peaks

Answer 18

Positive ions are accelerated by an electric field To a constant kinetic energy
The positive ions with m/z of 104 have the same kinetic energy as those with m/z of 118 and move faster
Therefore, ions with m/z of 104 arrive at the detector first

Question 19

Mr of diatomic elements

Answer 19

remember that there is 2!!!!!!!!! so ARx2

Question 20

percentage yield equation

Answer 20

actual/theoretical x100

Question 21

what alters Kp

Answer 21

increasing temperature

Question 22

what is the pH of a diuretic acid once it has fully dissociated when you know the concentration

Answer 22

times conc by two then find pH