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UNIT 2NATURE’S CHEMISTRY

(D) The chemistry of Cooking and the Oxidation of Food

SUBTOPIC ASSESSMENT

Multiple choice

Extended Response

TOTAL

17 33 50

Q1) Oil molecules are more likely to react with oxygen in the air than fat molecules.

During the reaction the oil molecules

A are reduced B become rancid C are hydrolysed D become unsaturated.

Q2) Enzymes are involved in the browning of cut fruit. One reaction taking place is:

Which of the following correctly describes the above reaction?

A Oxidation B Reduction C Hydrolysis D Condensation

Q3) Which of the following statements is correct for ketones?

A They are formed by oxidation of tertiary alcohols.

B They contain the group

C They contain a carboxyl group.

D They will not react with Fehling’s solution.

Q4)

Which of the following compounds is an isomer of the structure shown above?

A Butanal B Butanone C Butan-1-ol D Butanoic acid

Q5) Carvone is a natural product that can be extracted from orange peel.

Which line in the table correctly describes the reaction of carvone with bromine solution and with acidified potassium dichromate solution?

Q6) Vanillin and zingerone are flavour molecules.

Which line in the table correctly compares the properties of vanillin and zingerone?

Q7) A compound with molecular formula C6H12O2, could be

A hexanal B hexan-2-ol C hexan-2-one D hexanoic acid.

Q8) Which line in the table shows correct functional groups for aldehydes and ketones, and fats and oils?

Q9) A compound with the following structure is used in perfumes to help provide a sweet, fruity fragrance.

This compound could be classified as

A an ester B a ketone C an aldehyde D a carboxylic acid.

Q10) Which of the following organic compounds is an isomer of hexanal?

A 2-Methylbutanal B 3-Methylpentan-2-one C 2,2-Dimethylbutan-1-ol D 3-Ethylpentanal

Q11) When a protein is denatured

A its overall shape is distorted B its amide links are hydrolysed C it is broken into separate peptide fragments D it decomposes into amino acids

Q12) Which line in the table shows the correct functional group for each homologous series?

Q13) Which process is used to convert ethanal to ethanoic acid?

A Hydrogenation B Condensation C Hydration D Oxidation

Q14) Which two isomers would each produce an acid when warmed with acidified potassium dichromate solution?

Q15) Which alcohol could be oxidised to a carboxylic acid?

Q16) Which of the following structural formulae represents a tertiary alcohol?

17). 45 cm3 of a solution could be most accurately measured out using a

A 50 cm3 beaker B 50 cm3 burette C 50 cm3 pipette D 50 cm3 measuring cylinder.

Extended Response

Q1) Geraniol is one of the compounds found in perfume. It has the following structural formula and systematic name.

Linalool can also be present. Its structural formula is shown.

(A) State the systematic name for linalool. (1)

(B) Explain why linalool can be classified as a tertiary alcohol. (1)

Q2) Chocolate contains various compounds.

(a) Many of the flavour and aroma molecules found in chocolate are aldehydes and ketones.

Two examples are shown below.

Phenylethanal can be easily oxidised but 1,3-diphenylpropan-2-one cannot.

(i) Name a chemical that could be used to distinguish between these two compounds.

(1)(ii) Name the type of organic compound formed when phenylethanal is oxidised.

(1)

Q3) The structure of one of the first synthetic scents used in perfume is shown below.

(i) Name the family of carbonyl compounds to which this synthetic scent belong (1)

(ii) Complete the structure below to show the product formed when this scent is oxidised.

(1)

Q4) The element boron forms many useful compounds.

(a) Borane (BH3) is used to synthesise alcohols from alkenes. The reaction occurs in two stages

Stage 1 Addition Reaction

The boron atom bonds to the carbon atom of the double bond which already has the most hydrogens directly attached to it.

Stage 2 Oxidation Reaction

The organoborane compound is oxidised to form the alcohol.

(i) Name the alcohol produced in Stage 2. (1)

(ii) Draw a structural formula for the alcohol which would be formed from the alkene shown below.

(1)

Q5) Primary, secondary and tertiary alcohols can be prepared by the reaction of carbonyl compounds with Grignard reagents.

Step 1 The Grignard reagent reacts with the carbonyl compound

Step 2 The reaction of the product of Step 1 with dilute acid produces the alcohol.

(a) Describe the difference between a primary, a secondary and a tertiary alcohol. You may wish to include labelled structures in your answer. (1)

(b) Suggest a name for the type of reaction that takes place in Step 1. (1)

(c) Name the alcohol produced from butanal in the above reactions (1)

(d) The same Grignard reagent can be used to produce the alcohol below. (1)

Name the carbonyl compound used in this reaction. (1)

Q6) Cyanoacrylate adhesives are a range of high performance “super glues”. In its liquid form, super glue consists of cyanoacrylate monomers that rapidly polymerise in the presence of water to form a strong resin that joins two surfaces together. Cyanoacrylates have the general structure.

where R is a hydrocarbon group, eg -CH3.

a) Some super glues contain methyl 2-cyanoacrylate

Circle the ester link in this structure. (1)

b) If used incorrectly, super glue can rapidly cause your fingers to stick together.

(i) Suggest why super glue reacts rapidly on the surface of the skin. (1)

(ii) Super glue can be removed from the skin using propanone as a solvent.

Name the main type of van der Waals’ forces that would be formed between propanone and super glue.

(1)

c) Ethyl 2-cyanoacrylate is synthesised from ethyl 2-cyanoethanoate by a process based on the Knovenagel reaction.

(i) Name reactant A. (1)

(ii) Name this type of chemical reaction. (1)

(d) The adhesive strength of super glue can be altered by introducing different alkyl groups to the monomer.

Estimate the adhesive strength of super glue that contains the monomer shown below

(1)

(e) Super glues have been developed for medical applications.

(i) Medical tissue adhesive, containing octyl 2-cyanoacrylate, can be used for wound closures instead of sutures or stitches.

Draw a structural formula for octyl 2-cyanoacrylate.

(1)

Q7) a) One test for glucose involves Fehling’s solution. Circle the part of the glucose molecule that reacts with Fehling’s solution.

(1)

b) In solution, sugar molecules exist in an equilibrium in straight-chain and ring forms. To change from the straight-chain form to the ring form, the oxygen of the hydroxyl on carbon number 5 joins to the carbonyl carbon. This is shown below for glucose.

Draw the structure of a ring form for fructose. (1)

Q8) A student analysed a local water supply to determine fluoride and nitrite ion levels.

(a) The concentration of fluoride ions in water was determined by adding a red coloured compound that absorbs light to the water samples. The fluoride ions reacted with the red compound to produce a colourless compound. Higher concentrations of fluoride ions produce less coloured solutions which absorb less light. The student initially prepared a standard solution of sodium fluoride with fluoride ion concentration of 100 mg l-1.

(i) State what is meant by the term standard solution.

(1)

(ii) Describe how the standard solution is prepared from a weighed sample of sodium fluoride.

(2)

(iii) Explain why the student should use distilled or deionised water rather than tap water when preparing the standard solution.

(2)

Q9) Cooking changes the appearance and composition of foods.

Using your knowledge of chemistry, comment on the changes to food that may occur during cooking.

(3)

Q10) Ageing of wines Wine is a complex combination of many chemical compounds, which change as they interact with each other and their environment to give the wine its character.

A perfectly aged wine will have an optimal combination of three things: fruit flavours, fermentation flavours, and ageing flavours.

The wine-making process has two phases; the maturation phase and the ageing phase.

During the maturation phase, the grape juice is first fermented in large vats producing ethanol and smaller amounts of higher alcohols such as 3-methylbutan-1-ol and butan-2,3-diol. Exposure to oxygen at this stage causes the yeasts in the grape skins to multiply and allows other chemical reactions to take place. The wine is then transferred to wooden barrels and allowed to mature.

After maturation the wine is bottled and allowed to age. Wine experts recommend that bottled wine is stored at a constant 13 º C. At this temperature desirable chemical reactions take place slowly but unwanted chemical reactions are unable to take place.

Using your knowledge of chemistry, comment on how the maturation and ageing processes might affect the character of the wine.

(3)