exam q Flashcards
Which sample contains the greatest number of carbon atoms?
A 20.0g C6H5OH
B 30.0g C2H5COOH
C 40.0g CH3CHO
D 50.0g CH3OH
C.
Find moles of each compound then moles of carbon. (eg)
A= 20/Mr(C6H5OH) x6C = 1.2762
What is the correct equation for the incomplete combustion of butan-1-ol?
A CH3CH2CH2CH2OH + 1½O2- 4CO + 5H2
B CH3CH2CH2CH2OH + 2O2 -4CO + 5H2
C CH3CH2CH2CH2OH + 4O2- 4CO + 5H2O
D CH3CH2CH2CH2OH + 4½O2- 4CO + 5H2O
C
9Oxygens required. However there is already 1 oxygen on the reactant side so only 8 oxygen required.
8/2=4.
Which of the following statement(s) provide(s) evidence for the delocalised model of benzene
rather than the Kekulé model?
1) The enthalpy change of hydrogenation is more exothermic than expected.
2) Benzene only reacts with bromine in the presence of a halogen carrier.
3) The carbon-carbon bonds all have the same length
A 1, 2 and 3
B Only 1 and 2
C Only 2 and 3
D Only 1
B
1)hydrogenation being exothermic suggests less stable model which is untrue.
2) correct, needed to generate electrophilic substitution.
3)true.
How many σ- and π-bonds are in one molecule of buta-1,3-diene?
count single and double bond for sigma bond. (9)
only double bond for pi bond. (2)
A student thought that buta-1,3-diene can show stereoisomerism.
The student drew out skeletal formulae for the stereoisomers of buta-1,3-diene:
Explain, with a reason, whether the student is correct or incorrect.
Pmt nov 2021 q16
incorrect. 2 groups on one carbon atom (of C=C) are the same.
OR
C–C bond can rotate
n-13, is a CFC with the molecular formula CClF3.
In the upper atmosphere, the presence of Freon-13 can lead to ozone depletion.
Explain, with the aid of equations, how Freon-13 can lead to this ozone depletion.
Use ‘dots’ (*) to show the position of unpaired electrons.
FREE RADICAL SUBSTITUTION
initiation: CClF3 → CF3 * + Cl * (UV on arrow)
propagation: Cl * + O3 → *ClO + O2
*ClO + O → 2O2
One ibuprofen tablet contains 400mg of ibuprofen.
Calculate the number of ibuprofen molecules in one ibuprofen tablet.
Give your answer to 3 significant figures
ibuprofen molecular formula-C13H18O2
400/1000= 0.4g
Mr of ibuprofen= 206
0.4/206= 1.94x10-3mol
in molecules= 6.02x10-3 x1.94x10-3
=1.17x1021
Suggest why tablets based on a salt of ibuprofen should act faster in the body than ibuprofen.
salts are more soluble so it dissolves faster.
Myrcene, C10H16, is a naturally occurring hydrocarbon containing more than one
carbon-carbon double bond.Reaction of 204mg of myrcene with hydrogen gas produces a saturated alkane.
Calculate the volume of hydrogen gas, in cm3 and measured at RTP, needed for this reaction.
Show your working
n(myrcene) = 204 × 10–3/136.0 = 1.5(0) ×
10–3(mol)
3 double bonds so multiply by 3
Volume of H2 = 3 × 1.5(0) × 10–3
× 24000= 108 (cm3
Q17 2017 paper 2.
mechanism for nitration of benzoic acid
generation of electrophile
correct intermediate
regeneration of catalyst
A chemist carries out the reaction in Equation 17.1 using 4.97g of benzoic acid.
The chemist obtains 3-nitrobenzoic acid as an impure solid.
The chemist purifies the solid to obtain 4.85g of 3-nitrobenzoic acid.
Describe a method to obtain a pure sample of 3-nitrobenzoic acid from the impure solid,
determine the percentage yield and check its purity. 6 marks
- purification: Recrystallisation. Dissolve impure solid in minimum volume of hot
water/solvent. Cool solution and filter solid. Wash with cold water/solvent and dry - find moles of each acid and calculate percentage yield.
n(benzoic acid) used = 4.97/122 = 0.0407 mol)
n(3-nitrobenzoic acid) made = 4.85/167 = 0.0290 (mol)
percentage yield = 0.0290/0.0407 x 100 = 71.3 (%) - Checking purity:
Obtain melting point
Compare to known values
Pure sample will have a (sharp) melting point very
close to data book value
(ii) Apply your knowledge of the bonding in arenes to explain the trend in part (b)(i).
Q17 2017 paper 2.
Reactivity of phenol:
a (lone) pair of electrons on O is (partially)
delocalised/donated into the pi-system / ring
Reactivity of benzoic acid:
The –COOH group on benzoic acid is an electron withdrawing group
Links electron density in pi-bond to reactivity:
-In phenol electron density is higher AND
-The ring is more susceptible to attack
OR
-In benzoic acid electron density is lower AND The ring is less susceptible to attack
Sodium cyanide, NaCN, can be reacted with many organic compounds to increase the length
of a carbon chain.
(i) 1-Chloropropane, CH3CH2CH2Cl, reacts with ethanolic sodium cyanide by nucleophilic substitution.
Outline the mechanism for this reaction.
Include curly arrows, relevant dipoles and the structure of the organic product.
q18 markscheme 2017 p2
18 iv)Compound I is the monomer for the biodegradable polymer J.
Draw two repeat units of polymer J and suggest a reason why it is biodegradable.
its biodegradable because ester bond can be hydrolysed
Complete combustion of an organic compound forms 40cm3 of carbon dioxide and 40cm3 of
water vapour, under the same conditions of temperature and pressure.
Which molecular formula could the organic compound have?
A C3H8
B C2H2O
C C2H4O
D C2H3N
do complete combustion equation for each and whichever equation gives same moles of CO2 and H2O is correct.
C
Equal amounts of the four compounds are added to the same volume of water.
Which compound would produce the most acidic solution?
A CH3CONH2
B CH3COOH
C CH3COOCH3
D CH3COCl
D
β-Carotene is a naturally occurring unsaturated hydrocarbon found in carrots.
A β-carotene molecule contains 40 carbon atoms, has two rings, and a branched chain.
0.0200mol of β-carotene reacts with 5.28dm3 of hydrogen gas to form a saturated
hydrocarbon.
Using molecular formulae, construct a balanced equation for this reaction.
Include relevant calculations and reason
mol= vol/24
5.28/24=0.22mol of H2 gas
0.22/0.02= 11 double bonds
C40H78
C40H56 +11H2— C40H78
The rate of hydrolysis of a haloalkane depends on the halogen present.
State and explain how the halogen in the haloalkane affects the rate of hydrolysis.
the weaker the bond the faster the reaction
stronger bond takes longer to break
lower bond enthalpy reacts faster.C–I bond is the weakest
C–I has lower bond enthalpy than C–Br
C–Br is broken more easily/readily than
C–Cl.
C–Hal bond strength decreases down group (7)
Which statement(s) support(s) the delocalised model for the structure of benzene?
1 All carbon–carbon bonds have the same length.
2 The enthalpy change of hydrogenation of benzene is less exothermic than expected.
3 Bromine reacts with benzene less readily than with cyclohexene.
A 1, 2 and 3
B Only 1 and 2
C Only 2 and 3
D Only 1
A
19b)Chlorocyclohexane is hydrolysed with aqueous sodium hydroxide.
Outline the mechanism for this reaction.
Show curly arrows, relevant dipoles and the products.
Q19b 2018 june p2 mark scheme
A student hydrolyses a haloalkane, E, using the following method.
* 0.0100mol of haloalkane E is refluxed with excess NaOH(aq) to form a reaction mixture
containing an organic product F.
* The reaction mixture is neutralised with dilute nitric acid.
* Excess AgNO3(aq) is added to the reaction mixture. 1.88g of a precipitate G forms.
Organic product, F, has a molar mass of 74.0gmol−1 and has a chiral carbon atom.
(i) Draw a labelled diagram to show how the student would carry out the hydrolysis of
haloalkane E. (2m)
19c 2018 paper 2 mark scheme
A student hydrolyses a haloalkane, E, using the following method.
* 0.0100mol of haloalkane E is refluxed with excess NaOH(aq) to form a reaction mixture
containing an organic product F.
* The reaction mixture is neutralised with dilute nitric acid.
* Excess AgNO3(aq) is added to the reaction mixture. 1.88g of a precipitate G forms.
Organic product, F, has a molar mass of 74.0gmol−1 and has a chiral carbon atom.
Analyse the information to identify E, F and G.Show your working (3m)
G= AgBr
- calculate Mr by 1.88/0.01= 188gmol
- Mr of Ag = 107.9
188-107.9= 80.1 (closest to Mr of Br)
F/alcohol: butan-2-ol
E/haloalkane:
E is haloalkane of C4H9X with same halogen as G
AND
same carbon chain as F
Describe a chemical test to confirm that cinnamaldehyde and methylcinnamaldehyde
contain a carbonyl group.
How could the products of this test be used to distinguish between the two compounds?
Your answer should not include spectroscopy ( 3m)
(Add) 2,4-dinitrophenylhydrazine AND orange/yellow/red precipitate
Take melting point (of crystals)
Compare to known values/database
2018 JUNE p2 21cii) A general structure for esters J, L and M is shown below.
Where ‘R’ is an alkyl group.
Use the mass spectrometry results to deduce possible structures for esters J, L and M.
Mr of general structure= 137
J, L,M - 137 gives fragment ion
according to those value draw the R group.
J=15 (CH3)
L=43
M=43
43/12=3.6
3x12=36
43-36=7 ( 7H)
CH2CH2CH3
