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Question 1
a) | Describe a test-tube reaction that could be used to distinguish between each of the following pairs of compounds. For each pair, name the reagent(s) required, and the observation that would be made for each compound. |
i) | Butan-1-ol and 2-methylpropan-2-ol
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ii) | Propanoic acid and methyl propanoate
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iii) | Butanone and butanal
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iv) | Propane and 1-chloropropane
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v) | Benzene and cyclohexene
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Question 2
Test-tube reactions can be used to identify the functional groups in organic molecules. You are provided with samples of each of the four compounds. |
a) | Describe a chemical test that would produce a positive result with compounds A and B but a negative result with compounds C and D. You should describe what would be observed in the positive result.
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b) | Describe a chemical test would distinguish compound A from compound B. You should describe what would be observed in the positive result.
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c) | Describe a chemical test that would produce a positive result with compounds C and D but a negative result with compounds A and B. You should describe what would be observed in the positive result.
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d) | Describe a chemical test would distinguish compound C from compound D. You should describe what would be observed in the positive result.
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Question 3
Halogenoalkanes react with water to produce alcohols and halide ions. C4H9X + H2O ➔ C4H9OH + X- + H+ |
Test tube experiments can be carried out to investigate the relative rates of these substitution reactions. The halogenoalkanes 1‐chlorobutane, 1‐bromobutane and 1‐iodobutane can be used. Some of the steps in these experiments are
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State the purpose of adding ethanol to each of the test tubes.
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b) | Give one reason why the test tubes were put in the same beaker of hot water.
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c) | Give one reason why the test tubes were shaken after the addition of aqueous silver nitrate.
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d) | State how the halogen atom present in each halogenoalkane can be identified using observations from this experiment in part a).
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e) | Identify further reagents that can be added, including relevant observations, to confirm the identity of the halogen atom present in each halogenoalkane.
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Question 4
The structures for six naturally occurring organic compounds with pleasant smells, A–F, are shown below. |
a) | Identify the isomer(s) that would react when warmed with acidified potassium dichromate(VI). State the expected observation when acidified potassium dichromate(VI) reacts.
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b) | Identify the isomer(s) that would react with Tollens' reagent. State the expected observation when Tollens' reagent reacts.
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c) | Separate samples of A-F are warmed with ethanoic acid and a few drops of concentrated sulfuric acid. In each case the mixture is then poured into a solution of sodium hydrogencarbonate. Identify the isomer(s) that would react with ethanoic acid.
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d) | Suggest a simple way to detect if the ethanoic acid reacts with each organic compound.
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e) | Give a reason why the mixture is poured into sodium hydrogencarbonate solution.
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Question 5
This question is about three organic compounds: P, Q and R. P, Q and R have the same molecular formula, C6H12O. The table shows the observations made in some chemical tests on P, Q and R. |
a) | State what can be deduced about P from the positive test results.
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b) | The 1H NMR spectrum of compound P has only two peaks which are singlets with relative peak areas of 1 : 3. Use this information, your answer to part a) and the molecular formula to deduce the structure of P.
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c) | Name the functional groups present in Q, using observations from the table.
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d) | Compound Q is straight-chained and does not have geometric or optical isomers. Use this information, your answer to part c) and the molecula formula to deduce the structure of Q.
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e) | Deduce the type and classification of the functional group present in R, using observations from the table.
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f) | Compound R contains a five-membered carbon ring. Use this information, your deduction in part e) and the molecular formula to deduce the structure of R.
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Question 6
An ester C was hydrolysed by heating with aqueous sodium hydroxide. The resulting mixture was distilled to give an organic liquid D. The residue was acidified and the mixture purified to produce an organic liquid E. |
A spatula measure of phosphorus(V) chloride was added to separate portions of D and E. They both gave off a gas which produced steamy fumes in air and turned damp blue litmus paper red. |
a) | Identify the gas produced and the group in D and E indicated by this test.
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b) | A few drops of acidified potassium dichromate(VI) are added to a sample of D, and the mixture is heated. The colour of the mixture changes from orange to green. State what additional information this gives about D.
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c) | Give the formula for the ion responsible for the green colour of the mixture.
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d) | State two observations you would make when a small piece of sodium is added to liquid D.
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Question 7
The structures of three organic compounds A, B and C are shown. These compounds can be distinguished by simple test-tube reactions. |
a) | Give a reagent (or combination of reagents) that could be added separately to compounds A and B to distinguish between them. State what is observed in each case.
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b) | Give a reagent (or combination of reagents) that could be added separately to compounds A and C to distinguish between them. State what is observed in each case.
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c) | Give the steps to show how 2,4-dinitrophenylhydrazine could be used to distinguish between compounds A and C.
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Question 8
Compounds J, K, L and M are isomers of each other with the molecular formula C9H11NO. All four isomers contain a benzene ring. Two of the isomers contain a chiral centre. The results of six tests carried out on J, K, L and M are shown in the table. |
a) | Use the experimental results in the table above to determine the group(s), in addition to the benzene ring, present in each of the four isomers J, K, L and M.
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b) | Name the type of reaction occurring in test 5 that converts M into P + Q.
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c) | Suggest the identity of compounds P and Q.
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Question 9
The following three carbonyl compounds are structural isomers of C5H10O2. |
a) | Describe chemical tests that you could carry out in test-tubes to distinguish between compounds A, B and C. Include appropriate reagents and any relevant observations. Also include equations showing structures for the organic compounds involved.
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b) | 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.
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c) | Maleic acid is a stereoisomer of fumaric acid. The structure of the two acids are shown below. |
Describe chemical tests that can be carried out in a laboratory to identify the two functional groups in both acids.
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d) | Give the empirical formula of both acids.
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e) | State what type of geometric isomer maleic acid is.
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f) | Explain why maleic acid and fumaric acid are different compounds.
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Question 10
A series of tests is carried out on two organic liquids Y and Z. Each molecule of Y and Z contains one functional group. |
Test 1: Thionyl chloride, SOCl2 , was added to about 1 cm3 of each liquid in separate test tubes. Any gas evolved was tested with damp blue litmus paper. Observation with Y and with Z: Steamy fumes were given off. Damp blue litmus paper turned red. |
Test 2: About 1 cm3 of sodium hydrogencarbonate solution was added to 1 cm3 of each liquid in separate test tubes. Observation with Y: No visible change Observation with Z: A colourless gas was given off that turned limewater cloudy. |
a) | Identify the steamy fumes produced in test 1.
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b) | Identify the gas produced in test 2.
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c) | Using the results from tests 1 and 2 and the information at the start of the question, name the functional groups present in Y and Z.
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d) | Y and Z both have a molar mass of 46.0 g mol-1. Draw the displayed formula of Y and Z.
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