Chemistry 2017 wjec unit 2

Question 1

Molecular formula for a straight chained saturated halogenoalkane whos molecules have 50 carbon atoms and 2 chlorine atoms?

Answer 1

c50h100cl2

Question 2

Explain the effect of increasing temp on the rate of the reaction?

Answer 2

more particles have energy more than activation energy at a higher temp

Question 3

Structural formula of the monomer?

Answer 3

C double bond C
H3C
Cl

Question 4

To test for the presence of iodine in an organic compound, the compound?

Answer 4

is first heated with aqueous NaOH
followed by adding excess nitric acid
then aqueous silver nitrate into the mixture
if iodine is present, then a yellow ppt is seen

Question 5

Catalyst in reaction?

Answer 5

concentrated h2s04

Question 6

Standard enthalpy change of formation of ethanol?

Answer 6

2C(s) + 3H2(g)+11/2O2 —- C2H50H

Question 7

Why is difficult to measure the standard enthalpy change of formation of ethanol directly?

Answer 7

If carbon, hydrogen and oxygen - reacted either products would form

Question 8

Why is it difficult to use this apparatus to determine the enthalpy change of combustion of ethane?

Answer 8

ethane is a gas

Question 9

Explain the effect that each of the students errors has on the values they obtained?

Answer 9

effect of euan’s error - temp rise / loss in mass is very small so therefore greater percentage error

Question 10

Effect of carys’error?

Answer 10

mass of fuel used after boiling did not result in temperature rise therefore calculated value of delta combustion H is too small

Question 11

Standard enthalpy change of formation?

Answer 11

Delta H formation - 1371 = 2 x -394 + 3x-286
delta H formation - 275
-275 kjmol-1

Question 12

Amir said that hydrogen is the best fuel of these three in terms of the energy released by burning equal masses?

Answer 12

Amir = correct
C= 394/12= 32.8
H2 = 2.86/2.02 - 142
c2H5OH = 13,7.`46 = 29.6

Question 13

What can be deduced from the fact that 11.2 g reacts exactly with 32g of bromine?

Answer 13

0.2mol of c4h6 and 2 mole of bromine
so 1 double bond

Question 14

What type of reaction mechanism occurs when X reacts w bromine in the absence of light?

Answer 14

electrophillic addition

Question 15

What type of reaction mechanism occurs when X reacts with bromine in the presence of sunlight?

Answer 15

free radical substitution

Question 16

Use spectra to determine the identity of compound Y
use evidence to explain?

Answer 16

IR spectrum
link C-H to 30000 and C-Cl to 650
mass spectrum
Mr= 126/128/130
2 chlorine atoms present from peaks at 35 and 27

13 CNMR
2 different environment
comment on S values

1 HNMR
2 different hydrogen environments
same number of Hydrogens in each environment
1,4 dichlorobutane

Question 17

Collision theory to explain why the rate

Answer 17

at t - 200
concentration is lower
less frequent collisons

Question 18

determine if cobalt chloride is a better catalyst than manganese oxide in the decomposition of H202

Answer 18

Measure volume of gas at a particular time
use same amount of catalyst
use same volumes of same concentration of H202
better catalyst increase rate by a inute

Question 19

Type of mechanism between 2 chlorobutane and potassium cyanide?

Answer 19

nuceophilic subsititution

Question 20

when 2 chlorobutane is heated, 3 organic products are formed?

Answer 20

but 1 ene
but 2 ene
Z-but-2-ene

Question 21

What is the type of reaction taking place?

Answer 21

elimination

Question 22

Why are HFCS preferred to CFCS?

Answer 22

CFCS - destroy ozone layer
more exposed to uv radiation
cfcs produce cl radical
chlorine radical starts chain reaction
HFCS contain H / C-F bonds and these are too strong to be broken by light

Question 23

How can they get a good yield of pure ethanol?

Answer 23

Needs yeast/enzyme added to mixture
should be kept at body temp
must have some means of allowing co2
produced to escape
distillation needed to separate chain

Question 24

Calculate atom economy of process as a method of preparing ethanol?

Answer 24

180g of glucose produces 92/180 x 100=51.1%

Question 25

1 environmental consideration between choosing fermentation and hydration?

Answer 25

Hydration of ethene needs high temp
or hydration of ethene uses rich renewable petrol
fermentation uses renewable sugars

Question 26

Meaning of primary applied to alcohols?

Answer 26

Ol attached to a carbon that is attached to not more than 1 other carbon

Question 27

Structural formula and name of a tertiary alcohol that contains 5 carbon atoms?

Answer 27

2 methulbutan-2-ol

Question 28

one test that can be used to investigate whether an alcohol is secondary of tertiary?

Answer 28

acidified potassium dichromate
positive result for 2 degrees but negative result for 3 degrees
positive colour change = orange to green