Organic & Inorganic Practicals (OCR AS Chemistry)

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 Compound G Carboxylic 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. 

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

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. 

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.

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. 

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.

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. 

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. 

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. 

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.

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

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. 

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 - 53^oC

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

Label the diagram of the separating funnel given below.

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

State two improvements the student should make to this apparatus. 

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

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

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

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.

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

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

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.

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

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. 

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

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

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.

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

Outline the method to prepare the crude product.

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

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

Draw the apparatus required to purify the alcohol. 

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

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

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

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.

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.

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

[2]

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. 

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.