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Dodaj cały arkusz do zestawuHeat treatment at 90 °C is used to destroy spoilage micro-organisms in pineapple juice. The concentration of vitamin C was measured over 56 days in untreated juice and in heat-treated juice from the same batch. (i) Identify the dependent variable in this…
Ultraviolet (UV) light is being investigated as a way of killing micro-organisms in juice without heating it, so that less vitamin C is lost. The absorption spectrum of a dilute aqueous solution of sorbic acid, a preservative that is added to some bottled…
The concentration of vitamin C and the pH of five fruit juices were measured. Use the data to deduce whether pH and the concentration of vitamin C are correlated, giving a reason.
The vitamin C content of a juice can be found by titrating a sample against a standard iodine solution. Starch is used as the indicator: it forms a dark blue-black complex with the first excess of iodine once all the vitamin C has reacted.…
Calcium hydride, CaH2, is an ionic compound that forms a crystalline lattice of Ca2+ and H− ions. Deduce whether calcium hydride behaves as a Brønsted–Lowry acid or as a Brønsted–Lowry base, and justify your answer.
Sheets of pyrolytic graphite, which consists of many stacked layers of carbon atoms, are used in some phones to spread heat away from the processor. A sheet conducts heat very well parallel to its surface but poorly through its thickness. Suggest an…
Nomex® is a polyamide used in fire-resistant clothing. It forms when benzene-1,3-dicarboxylic acid reacts with benzene-1,3-diamine. Draw one repeating unit of Nomex®.
Glycine, H2NCH2COOH, loses a proton from its carboxyl group in alkaline solution to form the glycinate ion. The glycinate ion can bond to a copper(II) ion through two of its atoms, so it acts as a bidentate ligand. Explain how a glycinate ion bonds to a…
A sample of the protein is completely hydrolysed to a mixture of amino acids. Outline how paper chromatography can be used to identify the amino acids in this mixture when samples of the pure amino acids are available for comparison.
The concentration of protein in an extract can be found by mixing it with a dye that binds to protein and measuring the absorbance at 595 nm. The calibration line for standard protein solutions is shown. Its equation is y = 0.2903x + 0.0090, where y is the…
Palmitic acid, CH3(CH2)14COOH, and palmitoleic acid, CH3(CH2)5CH=CH(CH2)7COOH, which has a cis C=C double bond, both have a chain of sixteen carbon atoms. Predict which of the two fatty acids has the higher melting point and give two reasons for…
Sucrose, a disaccharide, forms when a molecule of glucose joins a molecule of fructose. State the type of reaction by which two monosaccharides join to form a disaccharide.
Methyl orange is a synthetic dye that is used as an acid–base indicator. The absorption spectrum of methyl orange in acidic solution is shown. Identify the colour of the acidic solution and give a reason. Use section 15 of the data booklet.
Name the hydrocarbon that is the main component of natural gas.
Outline one advantage and one disadvantage, other than cost, of burning natural gas instead of coal in a power station. Advantage: Disadvantage:
Some bacteria oxidize propanoate ions, CH3CH2COO−(aq), to carbon dioxide gas at the negative electrode of a microbial fuel cell. Air is supplied to the positive electrode and the cell operates in acidic conditions. Deduce the half-equation for the…
Describe, in detail, how a hydrogen–oxygen fuel cell and a secondary cell can each be used again and again without being replaced. Fuel cell: Secondary cell:
Benzocaine, a local anaesthetic, is the ethyl ester of 4-aminobenzoic acid. The crude product of its synthesis is purified by recrystallization. (i) Discuss two ways in which the melting point of the recrystallized benzocaine can show that it still contains…
A tablet contains either aspirin or paracetamol as its active ingredient. The structures of the two compounds and the IR spectrum of the active ingredient are shown. Deduce whether the active ingredient is aspirin or paracetamol, and give two reasons that…
Magnesium hydroxide is used as an antacid to neutralize excess stomach acid, which is hydrochloric acid. Write an equation for the reaction between magnesium hydroxide and hydrochloric acid, including state symbols.
Deduce which of aspirin and camphor gives 1H NMR signals with chemical shifts between 6.9 and 9.0 ppm, and give a reason. Use section 21 of the data booklet.
The mass spectrum of ibuprofen (Mr = 206) has a peak at m/z = 161. Suggest which fragment, lost from the molecular ion, could account for this peak. Use section 22 of the data booklet.