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Unit 2 Natural Products.

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1 Unit 2 Natural Products

Unit 2:- Natural Products (i) Both reactants and product are flammable. A water bath reduces chance of them catching fire. Acts as a condenser. (b) H H O H H H H H-C-C-O-C-C-C- C-C-H H H H H H H (c) 1 mole of ethanol (46g) will give 130g of ester at 100% yield. So 3.6g would give 10.17g At 70% yield = 7.12g 1. Ethyl pentanoate is an ester. It can be prepared in the lab. As shown below. (i) Why is a water bath used for heating? (ii) What is the purpose of the wet paper towel?   (b) Draw the structural formula for ethyl pentanoate.   (c) Starting with a mass of 3.6 g of ethanol, and a slight excess of pentanoic acid, a student achieved a yield of 70% of for ethyl pentanoate (mass of one mole = 130g) Calculate the mass of ester obtained.

3 2. Proteins are an important part of a balanced diet.
Identify the two true statements. A Proteins are a more concentrated energy source than carbohydrates. B Proteins are made by addition polymerisation. C Denaturing of proteins involves changes in the structure of the molecules. D Globular proteins are the major structural materials in animal tissues. E Proteins are compounds of nitrogen, carbon, hydrogen and oxygen. 3. The structure of a molecule found in olive oil can be represented as shown (a) Olive oil can be hardened using a nickel catalyst to produce a fat. (i) What type of catalyst is nickel in this reaction? (ii) In what way does the structure of a fat molecule differ from that of an oil molecule? (b) Olive oil can be hydrolysed using sodium hydroxide solution to produce sodium salts of fatty acids. (i) Name the other product of this reaction. (ii) Give a commercial use for sodium salts of fatty acid. C and E 3. (a) (i) Heterogeneous. (ii) Fat is saturated, (b) (i) Glycerol or propane-1,2,3-triol. (ii) Soap.

4 4. An ester can be prepared by the following sequence of reactions.
H H H H H – C – C – C – C – H H H Br H step 1 HBr removed Compound A CH3 – CH=CH-CH3 but-2-ene step step 2 CH3-CH2CH2CH2-OH CH3-CH2-CH-CH3 OH step oxidation Compound B step 4 condensation Ester CH3-CH2CH=CH2 Addition or hydration Orange to green Butanoic acid Oily layer formed (f) Solvents, perfume bases. Draw the structural formula for compound A What kind of reaction is shown by step 2? (c) What colour change would be seen when acidified dichromate is used to carry out step 3. (d) Name compound B. (e) What evidence would show that an ester had been formed in step 4? (f) Give one use for esters.

5 5. Tooth enamel contains a fibrous protein called collagen.
(a) Describe the difference between a fibrous protein and a globular protein. (b) Name the four elements present in all proteins. (a) Fibrous proteins are long, parallel protein chains with occasional cross links making up fibres. Globular proteins are folded into complex, almost spherical shapes. (b) Carbon, hydrogen, oxygen and nitrogen.

6 6. Biodiesel is a mixture of esters which can be made by heating rapeseed oil with
methanol in the presence of a catalyst. C21H39 —C—O—CH2 C21H39 —C—O—CH CH3OH C21H39 —C—O—CH X a triglyceride in Methanol a component rapeseed oil of biodiesel Name compound X (b) A typical diesel molecule obtained from crude oil has the molecular formula C16H34 (hexadecane). Other than the ester group, name a functional group present in biodiesel molecules which is not present in hexadecane. (c) Vegetable oils like rapeseed oil are converted into fats for use in the food industry. What name is given to this process? O O O O Glycerol OR propane-1,2,3-triol. C=C double bond. (c) Hydrogenation.

7 7. All enzymes are globular proteins.
What term is used to describe proteins which are not globular? (b) Catalase is an enzyme, contained in potatoes. A student was studying the effect of varying pH on the activity of catalase. The following apparatus was set up and left for 3 minutes. (i) What must be added to the side-arm test tube to study the enzyme activity at this pH? (ii) Describe how the enzyme activity at this pH can be measured. Fibrous. (i) Hydrogen peroxide solution. (ii) Counting the number of bubbles of oxygen in a set time can give a measure of the enzyme activity. The more active the enzyme o greater the number of bubbles of oxygen gas given off.

8 8. Two reactions of propanoic acid are shown.
Draw a structural formula for ester X. (b) (i) Give a name for compound Y, which reacts with propanoic acid to form sodium propanoate. (ii) Explain why solutions of sodium propanoate are alkaline. (a) O CH3-CH2 –C-O-CH3 (b) (i)Sodium hydroxide. (ii) Sodium propanoate dissolves to form sodium and propanoate ions Na+CH3CH2COO-(s) + H2O(l)  Na+(aq) + CH3CH2COO-(aq) In water there is this equilbrium H2O(l)  H+(aq) + OH-(aq) As propanoic acid is a weak acid the propanoate ions and hydrogen ions react to form molecules of propanoic acid CH3CH2COO-(aq) + H+(aq)  CH3CH2COOH(l) This removes hydrogen ions leaving an excess of hydroxide ions and so the solution is alkaline.

9 9. Enzymes are specific biological catalysts
9. Enzymes are specific biological catalysts. For example, trypsin, an enzyme produced in the pancreas, will catalyse the hydrolysis of only certain peptide links in a protein. (a) Draw the structure of a peptide link. (b) Trypsin has an optimum temperature of 37oC. Draw a curve to show how the enzyme activity varies with temperature. (a) O H - C – N – (b) See graph. The shape of the enzyme molecule is irreversibly changed so that it will no longer complement the shape of the substrate molecule. (c) Trypsin loses its activity if placed in a solution of very high pH. What happens to the enzyme to cause this loss in activity?

10 10. Ethanol and propanoic acid can react to form an ester.
(a) Draw the structural formula for this ester. (b) Draw a labelled diagram of the assembled apparatus that could be used to prepare this ester in the laboratory. (c) Due to hydrogen bonding, ethanol and propanoic acid are soluble in water whereas the ester produced is insoluble. In each of the boxes below, draw a molecule of water and use a dotted line where a hydrogen bond could exist between the organic molecule and the water molecule. ethanol propanoic acid   O CH3-CH2-O-H CH3-CH2-C-O-H H H O H H H – C – C – O – C – C – C – H H H H H (c) See boxes (a) Mixture of ethanol and propanoic acid. (c) See opposite H O H

11 11. Pyrolysis (thermal decomposition) of esters can produce two compounds, an alkene
and an alkanoic acid, according to the following equation. Draw a structural formula for the ester that would produce 2-methylbut-1-ene and methanoic acid on pyrolysis.

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