Which of the following are the essential components for fire? A Match box, fire wood and kerosene B Match box, fire wood and oxygen C Oxygen, fuel and fire wood D Oxygen, heat and match box E Oxygen, fuel and heat

A. Why is a gas burner good for heating in the fractional distillation? B. If the gas burner is lit with a gas lighter, is it a slow or fast reaction? Give a reason. Is it a slow or fast reaction in the absence of gas lighter? Give a reason.

1. Why is a gas burner good for heating in the fractional distillation? (2 mk)
2. If the gas burner is lit with a gas lighter, is it a slow or fast reaction? Give a reason. Is it a slow or fast reaction in the absence of gas lighter? Give a reason. (2 mk)

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Match the items in List A with the most suitable items in List B. List A (i) Increases colliding particles per A Increase in temperature time (ii) Favours endothermic reaction B Increase in pressure (iii) Increases the speed to reach equilibrium C Increase in concentration (iv) Favours the forward product of exothermic reaction D Decrease in pressure E Reversible reaction F Forward reaction G Product formation (v) Favours the forward product of endothermic reaction

1. Increases colliding particles per time (1 mk)
2. Favours endothermic reaction (1 mk)
3. Increases the speed to reach equilibrium (1 mk)
4. Favours the forward product of exothermic reaction (1 mk)
5. Favours the forward product of endothermic reaction (1 mk)
6. Increases the rate of reaction (1 mk)

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A certain metal when reacting with dilute acids produces hydrogen gas. (a) State the reason why the reaction is slow or fast? (b) Write the word equation for the reaction of Zinc with dilute hydrochloric acid. (c) In terms of the rate of reaction, what happens if zinc powder was used instead of granules. Give a reason.

1. State the reason why the reaction is slow or fast? (2 mk)
2. Write the word equation for the reaction of Zinc with dilute hydrochloric acid. (3 mk)
3. In terms of the rate of reaction, what happens if zinc powder was used instead of granules. Give a reason. (3 mk)

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A certain compound with the molecular mass of 28 was analyzed and found to be composed of 0.6 g of carbon and 0.1 g of hydrogen. (a) Work out its empirical formula and molecular formula. (b) Classify the compound into its homologous series.

1. Work out its empirical formula and molecular formula. (7 mk)
2. Classify the compound into its homologous series. (3 mk)

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The table below shows the titration of water sample with soap solution. Table 1 Water Sample Time (s) Mass (g) 0 110.20 2 110.10 4 110.00 6 108.50 8 107.20 10 107.20 (a) Why does the mass decrease initially and then becomes constant? (b) Write the chemical formula for the salt that is formed after heating. (c) In terms of the rate of reaction, what happens to the mass of the residue if zinc powder was used instead of granules.

1. Why does the mass decrease initially and then becomes constant? (4 mk)
2. Write the chemical formula for the salt that is formed after heating. (3 mk)
3. In terms of the rate of reaction, what happens to the mass of the residue if zinc powder was used instead of granules. (3 mk)

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Table 2 Water Sample Volume of Soap Solution (cm³) E 0.2 F 3.7 G 6.5 (a) Identify two things other than the volume of water that must be kept constant for such data to be measured. (b) (i) Identify which water sample has the highest hardness. Give a reason. (ii) Give three causes of hardness of water.

1. Identify two things other than the volume of water that must be kept constant for such data to be measured. (2 mk)
2. Identify which water sample has the highest hardness. Give a reason. (3 mk)
3. Give three causes of hardness of water. (5 mk)

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Consider the following substances: milk, copper, soap, steel, chlorine and sugar. (a) Identify from the list of substances, the components that are elements and compounds. (b) Give the difference between an element and a mixture.

1. Identify from the list of substances, the components that are elements and compounds. (4 mk)
2. Give the difference between an element and a mixture. (6 mk)

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Explain the reactivity of Carbon compared to other elements.

1. Give four reasons. (15 mk)

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(a) Arrange the following in order of decreasing reactivity: Potassium, Aluminium, Copper, Hydrogen, Magnesium. (b) Describe how a metal is extracted using reduction of its oxide with carbon. (c) Give four reasons why it is important to know the reactivity series of metals.

1. Arrange the following in order of decreasing reactivity: Potassium, Aluminium, Copper, Hydrogen, Magnesium. (3 mk)
2. Describe how a metal is extracted using reduction of its oxide with carbon. (7 mk)
3. Give four reasons why it is important to know the reactivity series of metals. (5 mk)

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(a) What happens when sulphur burns in air? (b) Describe the reaction between dilute Sulphuric acid and Zinc granules. (c) In what ways is Hydrogen useful to man?

1. What happens when sulphur burns in air? (5 mk)
2. Describe the reaction between dilute Sulphuric acid and Zinc granules. (5 mk)
3. In what ways is Hydrogen useful to man? (5 mk)

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(a) Compare and contrast the properties of ionic and covalent compounds. (b) In what circumstances would a covalent compound exhibit characteristics of an ionic compound? (c) Give four reasons why carbon is a versatile element. Explain its structure and bonding.

1. Compare and contrast the properties of ionic and covalent compounds. (5 mk)
2. In what circumstances would a covalent compound exhibit characteristics of an ionic compound? (3 mk)
3. Give four reasons why carbon is a versatile element. Explain its structure and bonding. (7 mk)

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Explain six effects of water pollution in Tanzania.

1. Explain six effects of water pollution in Tanzania. (15 mk)
2. Identify the acid and the base in the following reaction: HCl(aq) + H₂O(l) ⇌ H₃O⁺(aq) + Cl⁻(aq) (4 mk)
3. Calculate the pH of a solution with a hydroxide ion concentration of 1.0 x 10⁻⁵ M. (Kw = 1.0 x 10⁻¹⁴) (7 mk)

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Describe six ways that can be adopted by people in Tanzania to conserve water.

1. Describe six ways that can be adopted by people in Tanzania to conserve water. (15 mk)

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