CJC H2 CHEM P2 QP Prelim

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2 9647/02/CJC JC2 Preliminary Exam 2014 Planning (P) 1 FA1 is a solution of 1.00 mol dm-3 sodium hydroxide, NaOH. FA2 is a solution of 1.00 mol dm -3 acid which is either a monobasic with the formula HA, or dibasic with the formula H2A. You are required to determine the basicity of an acid (either monobasic or dibasic), based on the information given below and the planning of the procedure you have to undertake. Three separate experiments were carried out. Varying volumes of FA1 were measured and then added to different volumes of FA2 and the rise in temperatures, as a result of the mixing were recorded. The relevant measurements and results are tabulated below. Experiment 1 Experiment 2 Experiment 3 Volume of FA1 / cm3 25 25 50 Volume of FA2 / cm3 25 50 25 Temperature rise, ∆T / oC 6.9 4.6 9.1 (a) (i) Write a balanced equation for the reaction between FA1 and FA2 if the acid is monobasic. Do not omit spectator ions. ………………….…………………………….………………………………………………….. (ii) Write a balanced equation for the reaction between FA1 and FA2 if the acid is dibasic. Do not omit spectator ions. ………………….…………………………….………………………………………………….. [2] (b) You are provided with the following apparatus and materials: 1 thermometer 1 styrofoam cup Two 50 cm 3 measuring cylinders Sufficient FA1 solution Sufficient FA2 solution Plan a simple procedure by describing the steps you would carry out for Experiment 1 given above so as to make the relevant measurements and recordings. You are to use only the apparatus and materials listed above. ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... For Examiner’s Use

3 [Turn over 9647/02/CJC JC2 Preliminary Exam 2014 ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... [4] (c) Use the results of the relevant experiments given in the table above, explain clearly how the basicity of the acid is determined. Hence, state the basicity of the acid. [2] (d) (i) Hence, calculate the amount of heat evolved in Experiment 1. In your calculations, you are to assume that the specific heat capacity of the reaction mixture is 4.18 J g -1 K-1 and the density of the reaction mixture is 1 g cm-3. For Examiner’s Use

4 9647/02/CJC JC2 Preliminary Exam 2014 (ii) Using your answers to (d)(i) and the relevant equation in (a), calculate the enthalpy change of neutralisation, ∆Hneu. [2] (e) From your calculated ∆H neu value, state whether the acid is strong or weak. ………………….…………………………….……………………………………………………... [1] (f) Identify one source of error in your procedure and explain how you would minimise the error. ………………….…………………………….……………………………………………………... ………………….…………………………….……………………………………………………... [1] [Total: 12] For Examiner’s Use

5 [Turn over 9647/02/CJC JC2 Preliminary Exam 2014 2 Scuba diving is a form of underwater diving, in which a diver uses a self-contained underwater breathing apparatus (scuba) to breathe underwater. Scuba diving is an exhilarating sport, and thanks in part to the gas laws, it is also a safe activity for trained individuals who are in good health. A typical dive might be 12 to 19 m, but dives to 27 m are not uncommon. As seawater has a slightly higher density than fresh water, the pressure exerted by a column of 10 m of seawater is equivalent to a pressure of 1 atm. Pressure increases with increasing depth, so at a depth of 20 m, the pressure of the water will be 2 atm, and so on. The total pressure exerted on the diver is the sum of the atmospheric pressure and the pressure due to the column of water. (a) Consider a diver rising to the surface of the water from a depth of 6 m without breathing. (i) Calculate the total pressure exerted on a diver at 6 m. (ii) Show that, when the diver rises to the surface of the water, the volume of air trapped in the diver’s lungs would be increased by 1.6 times. The most important rule in scuba diving is to breathe continuously, especially when ascending, and to avoid holding breath underwater. This is to avoid barotrauma where physical damage to body tissues is caused by a difference in pressure between a gas space inside, or in contact with the body, and the surrounding waters. The sudden expansion of air can fatally rupture the membranes of the lungs. This is different in free diving, which relies on the diver’s ability to hold his or her breath until resurfacing, rather than on the use of a breathing apparatus. (iii) By considering the volume of air in the diver’s lungs, explain why barotrauma is not experienced for a free diver ascending at a depth of 6 m. ………………….…………………………….………………………………………………... ………………….…………………………….………………………………………………... ………………….…………………………….………………………………………………... ………………….…………………………….………………………………………………... [5] For Examiner’s Use

6 9647/02/CJC JC2 Preliminary Exam 2014 A scuba set is a breathing set that is carried entirely by an underwater diver and provides the diver with breathing gas at the ambient pressure. A breathing gas is usually a mixture of oxygen and nitrogen used for respiration. For instance, air is the most common and only natural breathing gas. Our bodies function best when oxygen gas has a partial pressure of 0.20 atm, as in the air we breathe. When a diver is submerged, a special valve automatically adjusts the pressure of the air breathed from the scuba tank to ensure that the air pressure equals the water pressure at all times. Although nitrogen gas may seem to be the obvious choice to mix with oxygen gas for use in the scuba tank, there is a serious problem associated with it. When the partial pressure of nitrogen gas exceeds 1 atm, enough o