Organic & Inorganic Practicals (OCR A Level Chemistry)

Exam Questions

3 hours40 questions
1a3 marks

The formation of a white precipitate with excess sodium hydroxide or excess sulfuric acid is often used as a way to identify Group 2 metal ions in solution.

Explain why the sodium hydroxide test or the sulfuric acid test should not be used on their own. Your answer should talk about the reactions of Group 2 metal ions with excess sodium hydroxide and with excess sulfuric acid.

1b1 mark

The test for the ammonium ion is the use of litmus paper as shown in Figure 1.

Figure 1
1-2

 

State the error shown in Figure 1 when testing for the ammonium ion.

1c2 marks

A student tested a solution known to contain a halide ion. It was found to produce a creamy yellow precipitate. Further testing showed that the precipitate did not dissolve. 

Identify the two reagents the student used to test the solution.

1d2 marks

Acid is used to test for the presence of the carbonate ion. The gas produced during this test has to be bubbled through limewater to prove that it is carbon dioxide. 

Write an ionic equation, including state symbols, for the reaction of the carbonate ion with acid to form carbon dioxide and one other product.

Did this page help you?

2a2 marks

Distillation is commonly performed in the school laboratory when converting alcohols into aldehydes and ketones.

Suggest two reasons why electric heating mantles are used instead of Bunsen burners for the distillation of alcohols and their reaction products.

2b2 marks

Propan-1-ol reacts with acidified potassium dichromate, K2Cr2O7, to form propanal and another product.

i)
Write a balanced symbol equation for the reaction which forms propanal, using [O] to represent the acidified potassium dichromate.
[1]
ii)
State the colour change for the reaction occurring in part (i).
[1]
2c1 mark

The boiling points of propan-1-ol and propanal are 97 °C and 49 °C respectively.  

Suggest why the boiling point of propanal is significantly lower than the boiling point of propan-1-ol.

2d1 mark

State the name of another substance that should be added to the flask before heating.

Did this page help you?

3a1 mark

A student prepared cyclohexene from cylcohexanol using concentrated phosphoric acid. They added 20 cm3 of cyclohexenol to a 50 cm3 pear shaped flask along with anti-bumping granules and slowly added 8 cm3 of the phosphoric acid. 

They distilled the apparatus and used a water bath to heat the flask. The distillate was added to a separating funnel in order to be purified. The student added sodium hydrogen carbonate to the funnel.

Explain why they added sodium hydrogen carbonate.

3b1 mark

Explain why the tap on the separating funnel must be opened and closed after shaking the contents.

3c2 marks

The student opens the tap of the separating funnel and runs off the lower layer and transfers the upper layer which contains crude cyclohexene into a conical flask.  

Describe how the student can obtain the pure organic liquid. 

3d2 marks

Explain how the student can test the pure organic liquid.

Did this page help you?

4a1 mark

This question is about the preparation of hexan-2-ol from hex-1-ene.

Draw the skeletal structure of hex-1-ene. 

4b2 marks

A student prepared hexan-2-ol by following the steps below.

  1. Prepare an ice bath in a 250 cm3 beaker 
  2. Using a measuring cylinder, measure out 5 cm3 of hex-1-ene and pour this into a boiling tube
  3. Plug the boiling tube with mineral wool and cool in the ice bath
  4. Using a measuring cylinder, measure out 5 cm3 of concentrated sulfuric acid 
  5. Once the hex-1-ene has been cooling for about 5 minutes, remove the mineral wool bung and slowly add the acid to the hex-1-ene
  6. Stir the mixture until it becomes one layer 
  7. Keep the boiling tube in the ice bath and add 10 cmof distilled water which will separate the reaction mixture into two layers
i)
Explain why mineral wool is required for this reaction. 
[1]
  
ii)
The reaction mixture separates into two layers, state whether the layer containing the hexan-2-ol will be the top or bottom layer.  
[1] 
4c1 mark

The hexan-2-ol is then separated and distilled.

Name the piece of equipment required for the separation of hexan-2-ol from the reaction mixture.

4d2 marks

The student tested a sample of hexan-2-ol and a sample of the original hex-1-ene. 

State the observation when potassium manganate(VI) solution is added separately to both solutions.

Did this page help you?

5a2 marks

This question is about the qualitative analysis of ions.

Calcium carbonate, CaCO3, reacts with sulfuric acid to form a salt, a gas and one other product. 

Write the balanced symbol equation, including state symbols for this reaction.

5b3 marks

When testing for halide ions, explain why silver nitrate, AgNO3, should be acidified with nitric acid and not hydrochloric acid. Your answer should include a balanced symbol equation, including state symbols.

5c4 marks

A student tested a solution to find out if it contained a sulfate ion. 

Explain how the student could test for the sulfate ion. In your answer include the positive test result and an ionic equation. 

5d2 marks

Write an equation, using structural formulae, for the reaction of bromine water with but-1-ene.

Did this page help you?

1a5 marks

Ethanol is a very common solvent found in all chemistry labs. It has a number of other uses and will undergo a variety of chemical reactions. 

Ethanol can be oxidised to form a carboxylic acid in a two step process, as shown

Ethanol rightwards arrowCompound G rightwards arrowCarboxylic acid

Draw and label the apparatus which would be necessary to ensure that ethanol was fully oxidised to the carboxylic acid and state the reagents and conditions necessary for the reaction. 

1b1 mark

During this reaction, anti-bumping granules are commonly used. Suggest why. 

1c2 marks

If the apparatus used in part (a) is set up differently, Compound G is formed. 

Name the product formed during this oxidation reaction and provide a reaction equation to demonstrate what is happening. 

1d1 mark

Regardless of how the apparatus is set up to oxidise an alcohol, a water bath or heating mantle is preferable to a Bunsen burner. 

Give a reason why this is the case.

Did this page help you?

2a6 marks

Some students were given three samples, sodium chloride, sodium bromide and sodium iodide. They were asked to complete a number of steps to identify each of the sodium halides. 

Complete the following table and give the relevant ionic equations for the reactions taking place. 

bfae7830-ebd1-48ef-85e9-4a0ad14f96d6

2b3 marks

When precipitates are formed they can be collected and dried. Describe how a student would collect a pure, dry sample of a precipitate that was formed.

2c3 marks

Other reactions involving sodium halides include the reactions with concentrated sulfuric acid. 

Write an equation to show the reaction which takes place between solid sodium bromide and concentrated sulfuric acid.

Explain why sodium bromide reacts differently to sodium chloride. 

2d1 mark

Like chlorine, bromine can be added to water to kill microorganisms and ensure that the water is safe to drink. 

Explain why chlorine and bromine can be used in this way, despite the fact that they are both toxic. 

Did this page help you?

3a4 marks

The alkaline earth metals of Group 2 are similar to the alkali metals of Group 1 but are somewhat less reactive. 

A group of students were doing a number of tests involving Group 2 cations and various anions.  

Describe how the students could test a solution of strontium chloride to prove the presence of strontium ions. Include any observations that the students would see. 

3b3 marks

The students then tested two samples - sodium carbonate and sodium sulfate - to find out which was which. They used a pipette to add small amounts of each sample to a boiling tube and then added a few drops of barium chloride solution to each boiling tube to test for the presence of sulfate ions. 

Identify a mistake which was made by the students and explain how this would affect their results.

3c2 marks

Describe a test and observation that the students could have done on the samples in part (b) to determine if carbonate ions were present. 

3d1 mark

Strontium carbonate is a white solid, which decomposes when heated in a crucible. 

Write an equation, including state symbols, for the thermal decomposition of strontium carbonate and explain why the mass of the white solid in the crucible would change during this reaction. 

Did this page help you?

4a2 marks

A student prepared a sample of a haloalkane from an alcohol using the following method:

  1. Measure 8 cm3 of 2-methylpropan-2-ol into a measuring cylinder and add to a separating funnel. 
  2. Add 20 cm3 of concentrated hydrochloric acid to the separating funnel in small portions of 2 - 3 cm3
  3. Gently shake the separating funnel at 2 minute intervals 
  4. Allow the layers to separate and dispose of the lower aqueous layer by opening the tap
  5. Add sodium hydrogen carbonate solution in small portions to the funnel
  6. Dispose of the queues layer and pour the organic layer into a clean dry conical flask and add two spatulas of magnesium sulfate 
  7. Distill the liquid and collect the distillate in the range of 47 - 53oC
i)
Explain why the student added sodium hydrogen carbonate to the separating funnel.

ii)
Explain why magnesium sulfate was added to the organic liquid collected.

4b1 mark

State and explain two improvements to the student’s method.

4c1 mark

Label the diagram of the separating funnel given below.

1-10

4d2 marks

The student set up the following distillation apparatus for the purification of the haloalkane produced.

6-2

State two improvements the student should make to this apparatus. 

Did this page help you?

5a5 marks

Outline a method for the preparation of cyclohexene from the reaction of cyclohexanol and concentrated phosphoric acid. 

5b3 marks

The student used 2.05 g of cyclohexanol and obtained 1.09 g of cyclohexene after purification. Calculate the percentage yield of cyclohexene. 

5c3 marks

Explain why the percentage yield calculated was less than 100%.

Did this page help you?

1a7 marks

A laboratory technician discovered four poorly labelled bottles each containing a solution of a different Group 2 metal compound. All four bottles had a white solid around the stopper and neck.

1-2_q1a-ocr-a-as--a-level-hard-sq

Give examples, with reasons, of chemical tests that the technician could perform to identify these different Group 2 metal compounds.

1b1 mark

The compound containing barium did not dissolve when sulfuric acid, hydrochlorc acid or water was added. Explain why.   

1c5 marks

The technician finds a fifth bottle, which she confidently identifies as calcium hydroxide and it is labelled as a saturated solution. 

Explain how the technician could determine if this solution is a fully saturated calcium hydroxide solution.

Did this page help you?

2a3 marks

A student is provided with 2 cm3 samples of the four different compounds shown.

3-2 

The student is set the challenge of distinguishing between the compounds using the minimum number of tests possible. They suggest the samples of each compound can be warmed with:

  1. Silver nitrate solution 
  2. Potassium dichromate solution

Evaluate the student’s suggestion. 

2b5 marks

Suggest and explain improvements to the student’s suggestion in part (a).

2c2 marks

Explain why the boiling point of compound Q is higher than compound S.

2d4 marks

The student is asked to separate a mixture of all four compounds by fractional distillation.

Explain the order in which the compounds will distil off.

Did this page help you?

3a6 marks

A student was tasked to hydrate hex-1-ene to form an alcohol.

Outline the method to prepare the crude product.

3b2 marks

Draw the skeletal structure of the alcohol formed and explain why this particular alcohol is the major product of the reaction.

3c3 marks

The student separated and dried the alcohol using anhydrous sodium carbonate and a separating funnel 

Draw the apparatus required to purify the alcohol. 

Did this page help you?

4a3 marks

A student is tasked with forming cylcohexene from cyclohexanol. They are provided with cyclohexanol, concentrated phosphoric acid, H3PO4, anti-bumping granules, distillation apparatus and an electric heating mantle.

The full mechanism for the formation of cyclohexene from cylohexanol is shown in Figure 1.

Figure 1

1-2_q4a-ocr-a-as--a-level-hard-sq

Using your knowledge of mechanisms, add in positive and negative charges to Figure 1 where required. 

4b4 marks

Explain how the student can prepare cyclohexene from cylohexanol with the apparatus given.

4c6 marks

Once the student has formed the cycloalkene they are given apparatus and compounds to purify the crude product.

 Explain how the student can form pure cyclohexene.

Did this page help you?

5a2 marks

A student prepared 2-chloro-2-methylpropane from 2-methylpropan-2-ol by following the method outlined below.

  1. Measure 8 cm3 of 2-methylpropan-2-ol in a measuring cylinder and pour into a separating funnel
  2. Using a fume hood, add 20 cm3 of concentrated hydrochloric acid to the separating funnel in of 2 - 3 cm3 portions
    • After each addition, ensure that the pressure is released by opening the tap / stopper 
  3. Leave the separating funnel to stand in the fume hood for 20 minutes and gently shake the separating funnel at 2 minute intervals 
  4. Allow the layers to separate and dispose of the lower aqueous layer by opening the tap
  5. Add sodium hydrogen carbonate solution in small portions to the funnel and gently shake the funnel
    • After each addition, ensure that the pressure is released by opening the tap / stopper 
  6. Dispose of the lower aqueous layer
  7. Pour the organic layer into a clean dry conical flask and add two spatulas of anhydrous magnesium sulfate 
  8. Once clear, decant the liquid into distillation apparatus 
  9. Distill the liquid and collect the distillate in the range of 47 - 53 oC

Explain what we can learn about the product from step 4.

5b4 marks

In step 5, the sodium hydrogen carbonate is added in small portions to the separating funnel.

i)
Explain why the sodium hydrogen carbonate is added in small portions.

[2]

ii)
Explain how addition of sodium hydrogen carbonate removes acidic impurities.
[2]

 

5c4 marks

The student adds anhydrous magnesium sulfate, in step 7, to remove the water from the product. They do this until the drying agent stops clumping. 

i)
Explain why adding too much drying agent will reduce the percentage yield.
 
[1]
ii)
Explain why the removal of water is classed as a physical change.
 
[1]
iiI)
Explain why the formation of hydrated magnesium sulfate is classed as a chemical change. 
 
[2]
5d2 marks

In steps 2 and 5, the instructions state that the pressure in the separating funnel must be released.

Explain why this should be done in step 2.

Did this page help you?