Inorganic & Organic Chemistry Core Practicals (Edexcel International AS Chemistry): Exam Questions

A student was provided with five test tubes labelled A, B, C, D and E, each containing a colourless aqueous solution.

The five solutions were known to be

barium chloride

nitric acid

potassium bromide

silver nitrate

sodium carbonate

The student carried out a series of tests to identify which test tube contained which solution.

i) The student tested each solution using universal indicator paper. Only solution A turned the paper red.

Identify solution A.

(1)

ii) The student mixed 1 cm³ of solution A separately with 1 cm³ of each of the other solutions.

There was no change for three of the mixtures but effervescence was observed when solution A was added to solution C.

Identify solution C.

(1)

iii) Write an ionic equation for the reaction between solution A and solution C. Include state symbols.

(2)

iv) The student then mixed 1 cm³ samples of the remaining solutions as shown in Table 1.

Table 1

Identify the three remaining solutions.

(3)

Solution B

Solution D

Solution E

Three of the cations in the compounds in (a) can be identified using flame tests.

Complete Table 2

Table 2

This question is about the reactions of three compounds with the formula C₆H₁₂O.

The compounds are cyclohexanol, Z-hex-3-en-1-ol and 1-methylcyclopentanol.

Give a chemical test to show the presence of the OH group in all three compounds, including the expected result.

i) Give a chemical test to show the presence of the carbon-carbon double bond in Z-hex-3-en-1-ol, including the expected result.

(2)

ii) The test you have given in (b)(i) is repeated with 1-methylcyclopentanol.

Give the observation for this test with 1-methylcyclopentanol.

(1)

Separate samples of each of these compounds are warmed with acidified potassium dichromate(VI).

Complete the table to give the colour changes observed, if any.

Spectroscopy provides information about the structure of these three compounds. Some infrared data is given in the table.

i) Identify the wavenumber range and the bond responsible for one peak which you would expect to see in the infrared spectra of all three compounds.

(1)

ii) Identify the wavenumber range and the bond responsible for one peak which you would expect to see in the infrared spectra of only one of the compounds.

(1)

iii) Give a reason why there is a peak at m/ z = 100 in the mass spectra of all three compounds.

(1)

iv) Fragmentation of 1-methylcyclopentanol results in a significant peak at m/ z = 85.

Suggest the structures of the two species formed when one bond in 1-methylcyclopentanol breaks resulting in the peak at m/ z = 85.

(2)

This question is about the preparation of anhydrous aluminium chloride, AlCl₃ , which reacts vigorously with water and must be stored in tightly sealed containers.

A sample of anhydrous AlCl₃ was prepared by passing chlorine gas over hot aluminium foil using the apparatus shown.

Granules of anhydrous calcium chloride are held between two ceramic wool plugs in the combustion tube.

i) Explain the purpose of the anhydrous calcium chloride.

(2)

ii) Give the reason why granules of anhydrous calcium chloride are used rather than powder.

(1)

The reaction occurring in Step 2 produces chlorine gas.

i) Identify the main hazard related to chlorine gas, giving the best way of minimising the risk when using this gas.

(2)

ii) Give a reason why the concentrated hydrochloric acid is added ‘drop by drop’ to the pear-shaped flask. (1)

Suggest why the heating of the aluminium in Step 3 is delayed by 20 s after the initial production of chlorine gas.

State how you would know the reaction is complete in Step 3.

Suggest the purpose of the potassium hydroxide in the absorption tube.

A sample of 1-bromobutane may be prepared by reacting butan-1-ol with sodium bromide and 50% concentrated sulfuric acid.

C₄H₉OH + NaBr + H₂SO₄ → C₄H₉Br + NaHSO₄ + H₂O

Procedure

Data

Suggest why the percentage yield of 1-bromobutane might be lower if the cold water bath was not used in Step 1.

i) State what must be added to the mixture in the flask before heating in Step 2.

(1)

ii) Draw a labelled diagram of the apparatus that you would use to heat the mixture under reflux in Step 2.

(3)

Purification of the product occurs in Steps 3–6.

i) State why sodium hydrogencarbonate solution is added in Step 4.

(1)

ii) Addition of sodium hydrogencarbonate solution in Step 4 causes vigorous effervescence.

Explain how the problem associated with Step 4 should be dealt with.

(2)

iii) Give the purpose of the anhydrous calcium chloride used in Step 5.

(1)

iv) State how the appearance of the organic liquid would change in Step 5.

(1)

For the final distillation in Step 6, a thermometer with a scale giving readings to the nearest 1°C was provided. .

Give a suitable temperature range for the collection of the pure 1-bromobutane.

A student was asked to prepare 20 cm³ of 1-bromobutane using the procedure described. The student knew that the percentage yield would be less than 100%.

i) Give one possible reason for the yield being less than 100%.

(1)

ii) After some research the student decided to use 21.0 g of butan-1-ol to prepare 20 cm³ of 1-bromobutane.

Calculate the percentage yield that the student expected to obtain.

(4)

The halogenoalkane 2-chloro-2-methylpropane may be prepared from 2-methylpropan-2-ol. Procedure

i) The concentrated hydrochloric acid used in Step 1 was labelled

Suggest two safety precautions, other than wearing safety spectacles and a laboratory coat, to minimise the risk when using this reagent in Step 1.

(2)

ii) Explain why the product in the organic layer in Step 2 does not mix with the aqueous layer.

(2)

iii) State why the tap of the separating funnel must be opened in Step 3.

(1)

iv) State why anhydrous sodium sulfate is added to the organic layer in Step 5.

(1)

v) Draw the apparatus required to distil the product and collect the distillate between 50°C and 52°C in Step 6.

(4)

The equation for the reaction is

(CH₃)₃COH(l) + HCl(aq) → (CH₃)₃CCl(l) + H₂O(l)

The final product after distillation weighed 2.62 g.

Calculate the percentage yield.

The choroalkane produced is used in an experiment to compare its rate of hydrolysis with two other halogenoalkanes.

A student dissolves separate 1.0 cm³ samples of each halogenoalkane in ethanol and adds 2 cm³ of silver nitrate solution.

The time taken for a precipitate to form is recorded. The results are shown.

The student concludes that both the structure of the halogenoalkane and the identity of the halogen affect the rate of hydrolysis.

Explain how the results support this conclusion.