Wrong answers chem

Question 1

Reaction with acyl chloride or acid anhydride - why does one with acyl chloride have higher atom economy

Answer 1

Mr of HCL is lower than Mr of COOH
smth along thos lines

Question 2

During purifying impure aspirin, why is a water bath used to heat the ethanol

Answer 2

Ethanol is flammable

Question 3

On the final step of purifying aspirin, why is the ethanol used in step 5 is ice cold

Answer 3

To prevent crystals reforming

Question 4

WHY CAN something act as nucleophile and a base

Answer 4

N atom has a lone pair of electrons
which can be donated to partially positive c

Question 5

Confirm on a spectrum between two compounds that have same molecular formula eg aldehyde and ketone

Answer 5

Compare the fingerprint region to a known spectra
to find exact match

Question 6

Using electron pair repulsion theory why cannot be used to predict the shape of CoCL4- ion

Answer 6

Too many electrons

Question 7

When water is put at top of condenser not bottom what is the problem

Answer 7

water does not fill the condenser / condenser is not cool
enough

Question 8

Why do amino acids separate on the TLC plate

Answer 8

Difference in the balance between solubility in solvent/mobile phase
and attraction to/retention on stationary phase

Question 9

Deescribe how a colorimeter can be used to measure the concentration of this solution accurately

Answer 9

prepare solutions of known concentration (in range covering0.3 mol dm-3 )

measure absorbance of solutions (in colorimeter)
plot results on graph and read off concentration (of provided
solution from graph)

Question 10

State why probe must be washed with a small volume of buffer solution before measuring the pH of the buffer solution

Answer 10

To avoid contamination of the buffer solution

Question 11

Suggest why the pH probe should not be washed with distilled water after each addition of acid

Answer 11

To avoid dilution of solution

Question 12

Why does adding water not change the volume of acid needed

Answer 12

Water is not a reagent
doesn’t affect the mol of acid or alkali

Question 13

Suggest why sILICON DIOCXIDE can be described as an acidic oxide even tho it is insoluble in water

Answer 13

Sio2 reacts with bases

Question 14

Describe how a pH meter is calibrated before use

Answer 14

measure pH of known conc
Plot a calibration graph

Question 15

Explain why there is no suitable indicator for the titration of a weak base with a weak acid

Answer 15

There is no steep part/ vertical region

Question 16

Why does addition of water not give an incorrect value for titre

Answer 16

Water is not a reactant
Water doesn’t react w any of the reagents

Question 17

Suggest why ethanol can be considered to be a carbon neutral fuel

Answer 17

CO2 released by combustion / fermentation / fuel cell / reaction with water
(atmospheric) CO2 taken up in photosynthesis

Question 18

State why more than the minimum energy is not used to ionise a sample

Answer 18

So no more than 1 electron is knocked out/ so only one electron is knocked out/ prevent further ionisation

Question 19

Reason for a stoppering flask in a titration

Answer 19

To prevent reaction with carbon dioxide (in the air)ORTo prevent evaporation (of water/from solution)

Question 20

Why chloroethanoic acid is a stronger acid than ehtanoic acid

Answer 20

M1 (Electronegative) chlorine withdraws electrons
M2 Stabilises/reduces charge on COO-
OR weakens O-H bond
OR makes O-H more polar

Question 21

Why does data books not usually contain values for kA of strong acids

Answer 21

M1 Strong acids (almost) completely dissociated/ionised OR not an equilibrium
OR equilibrium lies far to the right
M2 Ka value for strong acids tends to infinity/is very large OR can’t divide by zero in Ka

Question 22

Explain how vdw forces arise

Answer 22

Electron movement in first molecule / temporary dipole Induces a dipole in another molecule
(induced-temporary) attraction or
δ+ attracts δ- in different/adjacent molecules

Question 23

Conditions needed for fermentation of glucose

Answer 23

The conditions needed are: *Yeast
*No air
*temperatures 30 –40oC

Question 24

Equation of fermentation of glucose

Answer 24

C6H12O6 — 2 CH3CH2OH + 2 CO2

Question 25

What is a biofuel

Answer 25

A biofuel is a fuel produced from plants

Question 26

Advantages of fermentation 2

Answer 26

*sugar is a renewable resource *production uses low level technology / cheap equipment

Question 27

Disadvantages of fermentation 3

Answer 27

*batch process which is slow and gives high production costs *ethanol made is not pure and needs purifying by fractional distillation *depletes land used for growing food crops

Question 28

Advantages of hydration from ethene to ethanol 3

Answer 28

*faster reaction *purer product *continuous process (which means cheaper manpower)

Question 29

Disadvantages of hydration 3

Answer 29

*high technology equipment needed (expensive initial costs) *ethene is non-renewable resource (will become more expensive when raw materials run out) *high energy costs for pumping to produce high pressures

Question 30

Essential conditions of hydration from ethene to ethanol 3

Answer 30

high temperature 300 °C high pressure 70 atm strong acidic catalyst of conc H3PO4

Question 31

Explain why sodium oxide forms an alkaline solution when it reacts with water

Answer 31

Has O2- ions which react with water forming OH- ions