Lesmahagow High School

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1 Lesmahagow High School Higher Chemistry Unit 2 Problem Solving Practice

2 Organic Problem Solving Tutorial Questions 1a. Glycerol trinitrate is produced from glycerol. i. Draw a structural formula for glycerol. ii. Name a group of naturally occurring esters that can be hydrolysed to obtain glycerol. (b) When exploded, glycerol trinitrate decomposes to give nitrogen, water, carbon dioxide and oxygen. Balance the equation for this reaction: C 3 H s N 3 O 9(l) N 2(g) + H 2 O (g) + CO 2(g) + O 2(g) 2. An industrial method for the production of ethanol is outlined in the flow diagram. bi. Unreacted ethene is removed in separator A. Suggest how the separated ethene could be used to increase the efficiency of the overall process. ii. Name the process that takes place in separator B.

3 3. Self-test" kits can be used to check the quantity of alcohol present in a person's breath. The person blows through a glass tube until a plastic bag at the end is completely filled. The tube contains orange acidified potassium dichromate crystals that turn green when they react with ethanol. The chemical reaction causing the colour change is: 2- Cr 2 O 7 (aq) + 14H + (aq) + 6e - 2Cr 3+ (aq) + 7H 2 O (l) orange green The more ethanol present in the person's breath, the further along the tube the green colour travels. a. What is the purpose of the plastic bag? b. Why are the potassium dichromate crystals acidified? c. Name a carbon compound formed by the reaction of ethanol with acidified potassium dichromate crystals. 4a. Ethanol and propanoic acid can react to form an ester. i. Draw a structural formula for this ester. ii. iii. Draw a labelled diagram of the assembled apparatus that could be used to prepare this ester in the laboratory. Due to hydrogen bonding, ethanol and propanoic acid are soluble in water whereas the ester produced is insoluble. Copy each of the boxes below, draw a molecule of water and use a dotted line to show where a hydrogen bond could exist between the organic molecule and the water molecule, ethanol propanoic acid Pyrolysis (thermal decomposition) of esters can produce two compounds, an alkene and an a

4 5. Compound X is a secondary alcohol. a. Name compound X. b. Draw a structural formula for the tertiary alcohol that is an isomer of compound X. c. When passed over heated aluminium oxide, compound X is dehydrated, producing isomeric compounds, Y and Z. Both compounds Y and Z react with hydrogen bromide, HBr. Compound Y reacts to produce two products while compound Z reacts to produce only one product. Name compound Z. 6. Electrophoresis, widely used in medicine and forensic testing, involves the movement of ions in an electric field. The technique can be used to separate and identify amino acids produced by the breakdown of proteins. a. Name the type of reaction that takes place during the breakdown of proteins. bi. The amino acid, glycine, has the following structural formula: Like all amino acids, glycine exists as ions in solution and the charge on the ions depends on the ph of the solution. In solutions with low ph, glycine exists as a positively charged ion:

5 In solutions with a high ph, glycine exists as a negatively charged ion. Draw the structure of this negatively charged ion. ii. The table below shows the structures and molecular masses of three amino acids, A, Band C. A mixture of amino acids, A, Band C, was applied to the centre of a strip of filter paper which had been soaked in a solution of ph 2. All three amino acids exist as ions in this acidic solution. A high voltage was then applied across the filter paper. filter paper soaked in a solution of ph 2 The amino acid ions separate according to their charge and molecular mass. Copy the diagram above and indicate the approximate positions of A, B and C once electrophoresis has separated the ions.