P3-03

F1. Coal is the world’s most abundant fossil fuel, although its combustion can cause problems of pollution. As well as carbon, coal may contain significant amounts of sulfur and non-combustible inorganic material.

a. Describe the conditions under which coal was formed from plant remains.

b. State three pollutions formed when coal is burned directly.

c. One way to reduce the amount of pollution is to convert the coal to a gaseous fuel by heating with steam

i. State two combustible products of the reaction.

ii. Outline tow advantages and one disadvantage of coal gasification.

F2. Many portable electrical devices rely on various types of dry cell. The most common is zinc-carbon cell, although alkaline cells are becoming more common.

a. In the zinc-carbon cell, the space between the central carbon rod and zinc outer casing is filled with a paste containing ammonium chloride and manganese (IV) oxide.

i. One reaction occurring is 2NH₄⁺ + 2e^-

2NH + H₂, for which E°= + 0.73V. Use the Data Booklet to identify the other main reaction occurring, and hence determine the E value for the cell. Write the overall cell reaction.

ii. State the purpose of the manganese (IV) oxide.

b. State two advantages of the alkaline cell over the zinc-carbon cell.

c. A company manufactures a cell with a voltage of about 1.5 V. Suggest how the company could make each of the following.

i. A cell with a voltage of about 1.5 V, but producing more power.

ii. A battery with a voltage of about 6 V.

F3. Fuel cells have been described as the energy source of the future, because they are said to be non-polluting and can use renewable resources. One type uses hydrogen as the fuel and oxygen as the other substance consumed, with hot aqueous potassium hydroxide ad the electrolyte. The overall equation for the process is 2H₂ + O₂ ? 2H₂O, but the actual reactions taking lace are different.

a. Give the two half-equations for the reactions involving each reaction.

b. Each kilojoule of chemical energy released in the oxidation of hydrogen in the fuel cell costs more than that released in the combustion of gasoline. Explain why cells are considered to be more economical than gasoline engines.

D1. The demand for drinking water continues to be a problem for the world. About 97% of all the water on the planet is present in the seas and oceans and most of the rest is in ice caps or glaciers.

a. One method used to provide drinking water from sea water is reserved osmosis, which uses a partially permeable (semipermeable) membrane.

i. Outline the terms osmosis and partially permeable membrane.

Partially permeable membrane

ii. Explain the technique of reserve osmosis used to produce drinking water from sea water.

iii. Suggest one way in which a household could reduce the amount of water used.

b. Water that allows marine life to flourish needs high concentration of dissolved oxygen. Several factors can alter the oxygen concentration.

i. State how an increase in temperature affects the oxygen concentration.

ii. Eutrophication is a process that decreases the oxygen concentration of water. Explain how the accidental release of nitrates into a river can cause eutrophication.

c. Much drinking water is treated before use with either chlorine or ozone. State two advantages and two disadvantages of using ozone instead of chlorine.

D2. Waste water (sewage) from homes and industries varies greatly in its content. But it is desirable to treat it before it is returned to the environment, especially to reduce the Biological Oxygen Demand (BOD).

a. State what is meant by the term Biological Oxygen Demand

b. Describe the main features of the activated sludge process used in secondary treatment, and state the main impurities removed during this treatment.

Short Answer
	1.	F1. Coal is the world’s most abundant fossil fuel, although its combustion can cause problems of pollution. As well as carbon, coal may contain significant amounts of sulfur and non-combustible inorganic material. a. Describe the conditions under which coal was formed from plant remains. b. State three pollutions formed when coal is burned directly. c. One way to reduce the amount of pollution is to convert the coal to a gaseous fuel by heating with steam i. State two combustible products of the reaction. ii. Outline tow advantages and one disadvantage of coal gasification. F2. Many portable electrical devices rely on various types of dry cell. The most common is zinc-carbon cell, although alkaline cells are becoming more common. a. In the zinc-carbon cell, the space between the central carbon rod and zinc outer casing is filled with a paste containing ammonium chloride and manganese (IV) oxide. i. One reaction occurring is 2NH₄⁺ + 2e^-2NH + H₂, for which E°= + 0.73V. Use the Data Booklet to identify the other main reaction occurring, and hence determine the E value for the cell. Write the overall cell reaction. ii. State the purpose of the manganese (IV) oxide. b. State two advantages of the alkaline cell over the zinc-carbon cell. c. A company manufactures a cell with a voltage of about 1.5 V. Suggest how the company could make each of the following. i. A cell with a voltage of about 1.5 V, but producing more power. ii. A battery with a voltage of about 6 V. F3. Fuel cells have been described as the energy source of the future, because they are said to be non-polluting and can use renewable resources. One type uses hydrogen as the fuel and oxygen as the other substance consumed, with hot aqueous potassium hydroxide ad the electrolyte. The overall equation for the process is 2H₂ + O₂ ? 2H₂O, but the actual reactions taking lace are different. a. Give the two half-equations for the reactions involving each reaction. b. Each kilojoule of chemical energy released in the oxidation of hydrogen in the fuel cell costs more than that released in the combustion of gasoline. Explain why cells are considered to be more economical than gasoline engines.
	2.	D1. The demand for drinking water continues to be a problem for the world. About 97% of all the water on the planet is present in the seas and oceans and most of the rest is in ice caps or glaciers. a. One method used to provide drinking water from sea water is reserved osmosis, which uses a partially permeable (semipermeable) membrane. i. Outline the terms osmosis and partially permeable membrane. Osmosis Partially permeable membrane ii. Explain the technique of reserve osmosis used to produce drinking water from sea water. iii. Suggest one way in which a household could reduce the amount of water used. b. Water that allows marine life to flourish needs high concentration of dissolved oxygen. Several factors can alter the oxygen concentration. i. State how an increase in temperature affects the oxygen concentration. ii. Eutrophication is a process that decreases the oxygen concentration of water. Explain how the accidental release of nitrates into a river can cause eutrophication. c. Much drinking water is treated before use with either chlorine or ozone. State two advantages and two disadvantages of using ozone instead of chlorine. Advantages Disadvantages D2. Waste water (sewage) from homes and industries varies greatly in its content. But it is desirable to treat it before it is returned to the environment, especially to reduce the Biological Oxygen Demand (BOD). a. State what is meant by the term Biological Oxygen Demand b. Describe the main features of the activated sludge process used in secondary treatment, and state the main impurities removed during this treatment.