Chemistry Problem Set

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Chemistry Problem Set, 8 questions.

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International Pathway College
Foundation Programme
Chemistry Exam
May 2023
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For this paper you must have:
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A dark blue or black pen
A calculator approved by the University
NOTE:
• The maximum mark for this paper is 95.
• The marks for each question are indicated in brackets ().
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INSTRUCTIONS TO STUDENTS
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Fill in your exam candidate number in the box below
You have two hours to complete this paper.
Answer ALL questions.
Answers should be written in the spaces provided in this booklet.
Rough work should be done in this booklet. Draw a line through any work you do not
want marked
Use a dark blue or black pen.
You can use a pencil to draw diagrams
There are 8 questions on the paper. They should all be attempted
EXAM CANDIDATE NUMBER
Y
2
Spectroscopic data:
Table 1: Infrared wavenumber data
Wavenumber (cm-1)
2850-3300
750-1100
1620-1680
1680-1750
1000-1300
3230-3550
2500-3000
3300-3500
Bond
C-H
C-C
C=C
C=O
C-O
O-H (alcohols)
O-H (acids)
N-H
Table 2: 1H NMR Chemical shift data
Type of proton
ROH
RCH3
RNH2
R2CH2
R3CH
δ/ppm
0.5-5.0
0.7-1.2
1.0-4.5
1.2-1.4
1.4-1.6
R
2.1-2.6
C
C
O
H
O
C
Table 3: 13C NMR Chemical shift data
Type of carbon
C
C
5-40
R
C
Cl or Br
10-70
R
C
C
20-50
O
C
R
R
δ/ppm
N
3.1-3.9
25-60
H
RCH2Cl or Br
R
C
O
C
C
3.1-4.2
O
Alcohols, ethers
or esters
3.7-4.1
50-90
H
O
R
H
C
C
4.5-6.0
90-150
110-125
O
R
110-160
9.0-10.0
C
H
R
C
O
R
O
10.0-12.0
C
O
Esters or
acids
H
R
C
O
Aldehydes or
ketones
3
160-185
190-220
1) The popular analgesic drug aspirin can be made by reacting salicylic acid with
ethanoic anhydride:
a) State the name of a technique that could be used to find out whether the
reaction had finished. Do not give instrumental techniques in your answer
(i.e. do not include MS, NMR, IR etc)
……………………………………………………………………………
(1)
b) The aspirin formed in this reaction is a white crystalline solid. It can be
collected by vacuum filtration. Draw a labelled diagram to show the
equipment needed for vacuum filtration and how it can be setup.
Indicate on your diagram where the crystals of aspirin would be
collected.
(4)
4
c) State the name of a simple technique that could be used to show that the
aspirin is pure. Do not give instrumental techniques in your answer (ie. do not
include IR, MS, NMR etc). State the observation that you would make if the
sample was pure
Name of technique …………………………………………………………
Observation if sample is pure
…………………………………………………………………………………
…………………………………………………………………………………
…………………………………………………………………………………
(2)
d) Give the name of a technique that could be used to purify a crystalline product
on a large scale:
………………………………………………………………………………….
(1)
e) Calculate the mass of aspirin that can be made from 100g of salicylic acid and
excess ethanoic acid
…………………………………………………………………………………
…………………………………………………………………………………
…………………………………………………………………………………
………………………………………………………………………………….
(3)
f) The ethanoic anhydride used to make the aspirin is described as being
corrosive and to ‘avoid inhaling vapours’. Give two precautions that you
should take when handling this chemical.
Precaution 1 ……………………………………………………………..
Precaution 2 ………………………………………………………………
(2)
Questions continue on the next page.
5
2) A student carries out an experiment to determine the type of bonding in a number
of materials.
a) A student completes an experiment to find out the type of bonding in 4
different materials. Their results are shown below:
Melting point
Soluble in
water ?
Electrical
conductivity
as a solid
Electrical
conductivity
when molten
Appearance
A
Low
B
High
C
high
D
high
no
yes
no
no
no
no
yes
no
No
yes
yes
no
Colourless
gas
White
crystals
Grey,
shiny
sheet
Brown
crystals.
State the type of bonding present in each material
The bonding in substance A is ………………………………………..
The bonding in substance B is ………………………………………..
The bonding in substance C is …………………………………………
The bonding in substance D is ………………………………………….
(4)
b) Period 4 shows many of the same patterns as period 3.
i) Explain why calcium has a higher first ionisation energy than potassium.
…………………………………………………………………………
…………………………………………………………………………
…………………………………………………………………………
…………………………………………………………………………
…………………………………………………………………………
(3)
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ii) Explain why selenium has a lower first ionisation energy than arsenic.
…………………………………………………………………………
…………………………………………………………………………
…………………………………………………………………………
…………………………………………………………………………
…………………………………………………………………………
(3)
iii) Explain why scandium has a higher melting point than calcium
…………………………………………………………………………
…………………………………………………………………………
…………………………………………………………………………
…………………………………………………………………………
…………………………………………………………………………
(3)
3) A chemist wishes to find out the concentration of Fe2+ in a sample of iron tablets.
a) They decide to use a redox titration based on the reaction between potassium
dichromate and iron (II):
14H+ + Cr2O72- + 6Fe2+ → 7H2O + 2Cr3+ + 6Fe3+
i) State the oxidation state of the chromium in the dichromate ion
(Cr2O72-)
………………………….
(1)
ii) When the reaction is carried out, the iron tablets are crushed and then
dissolved in dilute sulphuric acid. Explain why it is necessary to use
sulphuric acid as the solvent – do not give answers based on dissolving
the tablet.
…………………………………………………………………………………
…………………………………………………………………………………
…………………………………………………………………………………
(1)
Questions continue on the next page
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iii) The iron is a transition element. Give one property of transition metals that
allows iron to be used in a redox titration.
…………………………………………………………………………………
…………………………………………………………………………………
…………………………………………………………………………………
(1)
b) The permanganate ion (MnO4-) can also be used in redox titrations.
i) The permanganate ion has a bright purple colour. Explain why.
………………………………………………………………………………………
………………………………………………………………………………………
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(4)
ii) Write a half equation to show the manganate ion being reduced to produce
the Mn2+ ion under acidic conditions.
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
(2)
iii) Iron (II) can be oxidised according to the half equation:
Fe2+ → Fe3+ +eUse your answer to part ii) and this half equation to write a balanced ionic
equation for the reaction between iron (II) ions and the permanganate ion
under acidic conditions.
………………………………………………………………………………………
………………………………………………………………………………………
………………………………………………………………………………………
(2)
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4) An enzyme called catalase can be used to catalyse the breakdown of hydrogen
peroxide:
A student carried out an investigation into the kinetics of this reaction and
found the following data:
[H2O2]
moldm-3
[catalase] x10-3
moldm-3
0.1
0.2
0.3
1
1
3
Rate of production of
production of oxygen
(cm3 s-1)
0.5
1.0
4.5
a) Deduce the order with respect to [H2O2]
…………………………………………………………………………………
………………………………………………………………………………….
………………………………………………………………………………….
(1)
b) Deduce the order with respect to [catalase]. Show any working you use to
derive your answer
…………………………………………………………………………………
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………………………………………………………………………………….
(1)
c) Calculate a value for k, the rate constant and give its units.
…………………………………………………………………………………
………………………………………………………………………………….
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(3)
Questions continue on the next page.
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d) The reaction is repeated at a temperature that is 10oC lower. Calculate the
new value of k
…………………………………………………………………………………
………………………………………………………………………………….
………………………………………………………………………………….
(1)
5) Some thermodynamic data is given in the table below.
HC
(kJ mol-1)
-2546
-3743
-286
—
Substance
Benzoic acid(s)
Benzyl alcohol(l)
H2(g)
H2O(l)
S
(J K-1 mol-1)
165.7
216.7
131.0
70
a) Write an equation to represent the enthalpy of combustion of solid benzoic
acid
…………………………………………………………………………………
(2)
b) Benzoic acid can be reduced to give benzyl alcohol liquid. The reaction can
be represented as:
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i) Use the data above to draw a Hess cycle and hence calculate the enthalpy
change for this reaction.
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
(3)
ii) Calculate the entropy change when benzoic acid acid is reduced to benzyl
alcohol.
……………………………………………………………………………
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(2)
iii) Use your answers to parts i and ii of this question to calculate the Gibbs
free energy for the reduction of benzoic acid and hence state whether the
reaction will be spontaneous at 298K.
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
(3)
Questions continue on the next page.
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iv) State whether the reaction will be spontaneous at a higher temperature.
Explain your reasoning.
……………………………………………………………………………
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(2)
6) Calculate the pH of each of the following solutions
a) 10cm3 of 0.245 moldm-3 sodium hydroxide (Kw=1×10-14 mol2dm-6)
…………………………………………………………………………………
………………………………………………………………………………….
………………………………………………………………………………….
(3)
b) 500cm3 of 0.245 moldm-3 butanoic acid (Ka=1.51×10-5 moldm-3)
…………………………………………………………………………………
………………………………………………………………………………….
………………………………………………………………………………….
(3)
c) A solution made by mixing the solutions from part a and part b of this
question.
…………………………………………………………………………………
………………………………………………………………………………….
………………………………………………………………………………….
…………………………………………………………………………………
………………………………………………………………………………….
………………………………………………………………………………….
(5)
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7) Look at the reaction scheme below:
a) Name compound P
……………………………………………………………………………..
(1)
b)
i) Draw the skeletal formula of compound R
(2)
ii) Give a mechanism for the reaction between compound Q and bromine in
step 2
(4)
Questions continue on the next page.
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c)
i) Name the functional groups that have been formed in step 4
…………………………………………….
(1)
ii) The reaction in step 4 proceeds in two stages – firstly one of the alcohol
groups in compound S reacts with one of the acyl chloride groups in
compound U. Then, a second reaction occurs where the second alcohol
reacts with the second acyl chloride group. This second stage closes the
ring.
Give a mechanism for the first part of the reaction between compounds S
and U in step 4. You only need show the reaction between ONE OH
group on compound S with ONE acyl chloride group on compound U. You
do not need to show the second, ring closure step.
(6)
8) A chemist has a sample of an unknown compound containing only carbon,
hydrogen and oxygen.
a)
i) The compound gives a silver mirror with Tollen’s reagent. What functional
group does it contain ?
……………………………….
(1)
ii) When the compound is added to sodium carbonate solution, no fizz is
seen. What functional group cannot be present in the molecule?
……………………………….
(1)
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b)
i) The compound gives peaks at =210ppm and =206ppm in its 13C NMR
spectrum (as well as other peaks). What can be deduced about the
molecule from these two peaks ?
…………………………………………………………………………
………………………………………………………………………….
………………………………………………………………………….
(2)
ii) The compound contains two C atoms that both give a peak at =25ppm in
the 13C NMR spectrum
What can be deduced from the fact that two C atoms both have
the same chemical shift ?
…………………………………………………………………………
………………………………………………………………………….
(1)
c) There are a number of peaks in the compound’s mass spectrum including a
molecular ion peak at m/z=114 (M+) and a strong fragment peak at m/z=15.
i) The compound contains 10 hydrogen and 2 oxygen atoms in its chemical
formula. State the number of carbon atoms in its formula.
Space for working: ..………………………………………………
………………………………………………………………………..
No. of carbon atoms= ……….
(2)
ii) Suggest a possible fragment that gives rise to the peak at m/z=15
………………………………………………………
(1)
Questions continue on the next page.
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d) The compound gives the following peaks in its 1H NMR spectrum:
Chemical
shift (, ppm)
Integration
Splitting
pattern
1.39
6H
s
2.14
3H
s
9.70
1H
s
Assignment
i) Assign a possible fragment that gives rise to each of the signals in the
table above. Make sure your fragment explains the integration and
splitting pattern. Write your answer in the table above.
(5)
ii) Draw a displayed formula in the space below to show the identity of the
unknown molecule:
(2)
END OF QUESTIONS
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