THE UNITED REPUBLIC OF TANZANIA
CERTIFICATE OF SECONDARY EDUCATION EXAMINATION
CHEMISTRY
CODE: 041/1
TIME: 3 HOURS
INSTRUCTIONS
1. This paper consists of Sections A, B and C with a total of 11 questions.
2. Answer ALL questions in Sections A and B.
3. Answer TWO questions from Section C.
4. Show all necessary working in calculation questions.
5. Use the following relative atomic masses where necessary:
H = 1, C = 12, O = 16, Na = 23, Mg = 24, Al = 27, S = 32, Cl = 35.5, K = 39, Ca = 40, Fe = 56, Cu = 64, Zn = 65.
6. Where necessary, use molar gas volume at room temperature and pressure as 24 dm³ mol⁻¹.
SECTION A: OBJECTIVE QUESTIONS
16 MARKS
1. Choose the correct answer from the alternatives A, B, C and D.
(i) Which of the following is a chemical change?
A. Melting of ice
B. Dissolving sugar in water
C. Rusting of iron
D. Breaking of glass
(ii) An atom has 17 protons and 18 neutrons. Its mass number is:
A. 17
B. 18
C. 35
D. 36
(iii) Which gas turns limewater milky?
A. Oxygen
B. Hydrogen
C. Carbon dioxide
D. Nitrogen
(iv) The pH of a strong acid is usually:
A. 1–3
B. 7
C. 8–10
D. 12–14
(v) Which method is best for separating ethanol from water?
A. Filtration
B. Fractional distillation
C. Decantation
D. Sublimation
(vi) Which metal is extracted from its ore by electrolysis?
A. Sodium
B. Iron
C. Copper
D. Zinc
(vii) The functional group present in alcohols is:
A. –COOH
B. –OH
C. –CHO
D. –CO–
(viii) Which of the following is an alkene?
A. CH₄
B. C₂H₆
C. C₂H₄
D. C₃H₈
(ix) A substance that speeds up a chemical reaction without being permanently consumed is called:
A. Reactant
B. Catalyst
C. Product
D. Solvent
(x) Which gas is produced when dilute hydrochloric acid reacts with zinc?
A. Oxygen
B. Chlorine
C. Hydrogen
D. Carbon dioxide
2. Match the items in List A with the correct responses in List B.
LIST A
(i) HCl
(ii) NaOH
(iii) CO₂
(iv) NH₃
(v) CaCO₃
(vi) CuSO₄
LIST B
A. Copper(II) sulphate
B. Calcium carbonate
C. Sodium hydroxide
D. Hydrochloric acid
E. Ammonia
F. Carbon dioxide
G. Sodium chloride
H. Calcium oxide
SECTION B: SHORT ANSWER AND STRUCTURED QUESTIONS
54 MARKS
3. (a) Define the following terms:
(i) element
(ii) compound
(iii) mixture
(b) State two differences between a mixture and a compound.
(c) Give one example of:
(i) an element
(ii) a compound
(iii) a mixture.
4. (a) Complete the following equations:
(i) Mg + O₂ → __________
(ii) Zn + HCl → __________ + __________
(iii) CaCO₃ → __________ + __________
(iv) HCl + NaOH → __________ + __________
(b) Balance the following equations:
(i) ___Fe + ___O₂ → ___Fe₂O₃
(ii) ___Al + ___O₂ → ___Al₂O₃
5. A student was given a mixture containing sand, common salt and water.
(a) Name the method used to separate:
(i) sand from the mixture
(ii) common salt from the solution
(b) Describe how the student can obtain dry common salt crystals.
(c) Explain why filtration cannot be used to separate dissolved salt from water.
6. (a) Define relative atomic mass.
(b) Calculate the relative formula mass of CaCO₃.
(c) Calculate the number of moles in 11 g of CO₂.
(d) Calculate the mass of 0.5 mol of NaOH.
7. Hydrogen gas was prepared by reacting zinc granules with dilute hydrochloric acid.
(a) Write a balanced chemical equation for the reaction.
(b) Name the gas produced.
(c) State one test for the gas.
(d) Give two precautions that should be observed during the preparation of hydrogen.
(e) Explain why the first portion of gas produced should not immediately be collected for use.
8. (a) Define an acid and a base according to the Arrhenius concept.
(b) State three properties of acids.
(c) State three properties of bases.
(d) Write a balanced equation for the reaction between hydrochloric acid and sodium hydroxide.
(e) Name the type of reaction involved.
SECTION C: STRUCTURED/ESSAY QUESTIONS
30 MARKS
Answer TWO questions only.
9. PERIODIC TABLE AND CHEMICAL BONDING
(a) Explain the meaning of:
(i) atomic number
(ii) mass number
(iii) isotope.
(b) An atom X has atomic number 12 and mass number 24.
(i) State the number of protons.
(ii) State the number of neutrons.
(iii) State the number of electrons in a neutral atom.
(iv) Write its electronic arrangement.
(c) Explain how an ionic bond is formed between sodium and chlorine atoms.
(d) State two properties of ionic compounds.
10. ORGANIC CHEMISTRY
(a) Define an organic compound.
(b) Give the general formula of:
(i) alkanes
(ii) alkenes
(iii) alkynes.
(c) Write the structural formulae of:
(i) ethane
(ii) ethene
(iii) ethyne
(iv) ethanol.
(d) State two differences between saturated and unsaturated hydrocarbons.
(e) Explain one chemical test that can be used to distinguish an alkane from an alkene.
11. CHEMICAL REACTIONS, ENERGY AND INDUSTRIAL CHEMISTRY
(a) Define:
(i) exothermic reaction
(ii) endothermic reaction
(iii) activation energy.
(b) State three factors that affect the rate of a chemical reaction.
(c) Explain how each of the following affects the rate of reaction:
(i) temperature
(ii) concentration
(iii) surface area.
(d) State two uses of catalysts in industry.
(e) Give two environmental problems associated with industrial chemical processes.
CHEMISTRY 041/1
FORM FOUR THEORY
MARKING SCHEME
TOTAL: 100 MARKS
SECTION A
15 MARKS
1. Multiple Choice — 10 marks
(i) C — Rusting of iron
(ii) C — 35
(iii) C — Carbon dioxide
(iv) A — 1–3
(v) B — Fractional distillation
(vi) A — Sodium
(vii) B — –OH
(viii) C — C₂H₄
(ix) B — Catalyst
(x) C — Hydrogen
2. Matching Items — 6 marks
(i) D — Hydrochloric acid
(ii) C — Sodium hydroxide
(iii) F — Carbon dioxide
(iv) E — Ammonia
(v) B — Calcium carbonate
(vi) A — Copper(II) sulphate
SECTION B
54 MARKS
3. BASIC CHEMICAL CONCEPTS — 9 MARKS
(a)
(i) Element:
A pure substance made up of only one type of atom. — 1 mark
(ii) Compound:
A pure substance formed when two or more different elements chemically combine in fixed proportions. — 1 mark
(iii) Mixture:
A physical combination of two or more substances which are not chemically combined. — 1 mark
(b) Differences:
(i) A mixture can be separated by physical methods, while a compound requires chemical methods. — 1 mark
(ii) Components of a mixture retain their individual properties, while a compound has properties different from its constituent elements. — 1 mark
(c)
(i) Element: iron/oxygen/copper — 1 mark
(ii) Compound: water/sodium chloride/carbon dioxide — 1 mark
(iii) Mixture: air/soil/salt solution — 1 mark
Total = 9 marks
4. CHEMICAL EQUATIONS — 9 MARKS
(a)
(i) 2Mg + O₂ → 2MgO — 1 mark
(ii) Zn + 2HCl → ZnCl₂ + H₂ — 1 mark
(iii) CaCO₃ → CaO + CO₂ — 1 mark
(iv) HCl + NaOH → NaCl + H₂O — 1 mark
(b)
(i) 4Fe + 3O₂ → 2Fe₂O₃ — 2 marks
(ii) 4Al + 3O₂ → 2Al₂O₃ — 2 marks
Correct coefficients and formulae should both be considered.
Maximum = 9 marks
5. SEPARATION OF MIXTURES — 9 MARKS
(a)
(i) Filtration — 1 mark
(ii) Evaporation/crystallisation — 1 mark
(b) Procedure:
(i) Heat the salt solution gently to evaporate some water. — 1 mark
(ii) Allow the concentrated solution to cool so crystals form. — 1 mark
(iii) Filter the crystals. — 1 mark
(iv) Wash the crystals with a small amount of cold distilled water and dry them. — 1 mark
Any four relevant steps = 4 marks
(c) Filtration cannot separate dissolved salt because the salt particles are small enough to pass through the filter paper with the water. — 2 marks
Total = 9 marks
6. MOLES AND FORMULAE — 9 MARKS
(a) Relative atomic mass:
The weighted average mass of atoms of an element compared with 1/12 of the mass of a carbon-12 atom. — 2 marks
(b) CaCO₃:
Ca = 40
C = 12
O₃ = 48
Mr = 40 + 12 + 48
Mr = 100
Answer = 100 — 2 marks
(c) CO₂:
Mr = 12 + (16 × 2)
= 44
Moles = mass/Mr
= 11/44
= 0.25 mol
Answer = 0.25 mol — 3 marks
(d) NaOH:
Mr = 23 + 16 + 1
= 40
Mass = moles × Mr
= 0.5 × 40
= 20 g
Answer = 20 g — 2 marks
Total = 9 marks
7. PREPARATION OF HYDROGEN — 9 MARKS
(a)
Zn + 2HCl → ZnCl₂ + H₂ — 2 marks
(b)
Hydrogen gas — 1 mark
(c)
Bring a burning splint near the gas; hydrogen burns with a characteristic "pop" sound. — 2 marks
(d) Any two precautions:
(i) Keep the apparatus away from flames until the initial air has been displaced. — 1 mark
(ii) Use dilute hydrochloric acid carefully. — 1 mark
(iii) Ensure the apparatus is properly fitted to prevent leakage. — 1 mark
(e)
The first gas contains air already present in the apparatus and may form an explosive mixture with hydrogen. — 2 marks
Total = 9 marks
8. ACIDS, BASES AND SALTS — 9 MARKS
(a)
Acid:
A substance which produces hydrogen ions (H⁺) when dissolved in water. — 1 mark
Base:
A substance which produces hydroxide ions (OH⁻) in aqueous solution. — 1 mark
(b) Properties of acids — any three:
(i) Have pH below 7.
(ii) Turn blue litmus red.
(iii) React with some metals to produce hydrogen.
(iv) React with bases to form salt and water.
(v) Conduct electricity in aqueous solution.
3 × 1 = 3 marks
(c) Properties of bases — any three:
(i) Have pH above 7.
(ii) Turn red litmus blue.
(iii) Neutralise acids.
(iv) Feel slippery/soapy.
(v) Conduct electricity in aqueous solution.
3 × 1 = 3 marks
(d)
HCl + NaOH → NaCl + H₂O — 1 mark
(e)
Neutralisation reaction — 1 mark
Total = 11 marks
NOTE: The original Section B allocation has an internal mismatch if Question 8 is awarded 11 marks while the section is stated as 54 marks. For a strict 100-mark paper, the examiner should cap Question 8 at 9 marks by awarding three properties collectively across (b) and (c), or revise the section allocation before administration.
SECTION C
30 MARKS
Candidates answer TWO questions.
Each question = 15 marks.
9. PERIODIC TABLE AND CHEMICAL BONDING — 15 MARKS
(a)
(i) Atomic number:
Number of protons in the nucleus of an atom. — 1 mark
(ii) Mass number:
Total number of protons and neutrons in the nucleus. — 1 mark
(iii) Isotope:
Atoms of the same element having the same atomic number but different mass numbers. — 1 mark
(b) Atom X:
Atomic number = 12
Mass number = 24
(i) Protons = 12 — 1 mark
(ii) Neutrons = 24 − 12 = 12 — 1 mark
(iii) Electrons = 12 — 1 mark
(iv) Electronic arrangement = 2, 8, 2 — 1 mark
(c) Formation of ionic bond:
Sodium has one electron in its outer shell and loses this electron to form Na⁺. — 2 marks
Chlorine gains one electron to form Cl⁻. — 1 mark
The oppositely charged ions attract each other, forming an ionic bond/compound NaCl. — 1 mark
(d) Any two properties:
(i) High melting and boiling points.
(ii) Conduct electricity when molten or dissolved in water.
(iii) Usually form crystalline solids.
(iv) Generally soluble in water.
2 × 1 = 2 marks
Total = 15 marks
10. ORGANIC CHEMISTRY — 15 MARKS
(a)
An organic compound is a compound mainly containing carbon, usually bonded with hydrogen and/or other elements. — 2 marks
(b)
(i) Alkanes: CₙH₂ₙ₊₂ — 1 mark
(ii) Alkenes: CₙH₂ₙ — 1 mark
(iii) Alkynes: CₙH₂ₙ₋₂ — 1 mark
(c)
(i) Ethane: CH₃–CH₃ — 1 mark
(ii) Ethene: CH₂=CH₂ — 1 mark
(iii) Ethyne: HC≡CH — 1 mark
(iv) Ethanol: CH₃–CH₂–OH — 1 mark
(d) Differences:
(i) Saturated hydrocarbons contain only single carbon-carbon bonds, while unsaturated hydrocarbons contain at least one double or triple bond. — 1 mark
(ii) Saturated hydrocarbons generally undergo substitution reactions, while unsaturated hydrocarbons readily undergo addition reactions. — 1 mark
(e)
Add bromine water. An alkene decolourises bromine water, while an alkane does not under ordinary conditions. — 2 marks
Total = 15 marks
11. CHEMICAL REACTIONS, ENERGY AND INDUSTRIAL CHEMISTRY — 15 MARKS
(a)
(i) Exothermic reaction:
A reaction that releases heat energy to the surroundings. — 1 mark
(ii) Endothermic reaction:
A reaction that absorbs heat energy from the surroundings. — 1 mark
(iii) Activation energy:
The minimum energy required for reactant particles to start a chemical reaction. — 1 mark
(b) Any three factors:
(i) Temperature
(ii) Concentration
(iii) Surface area
(iv) Pressure for gases
(v) Catalyst
3 × 1 = 3 marks
(c)
(i) Temperature:
Increasing temperature increases the kinetic energy of particles, causing more frequent and successful collisions; therefore the reaction becomes faster. — 2 marks
(ii) Concentration:
Increasing concentration increases the number of reacting particles per unit volume, increasing collision frequency and reaction rate. — 2 marks
(iii) Surface area:
Increasing surface area exposes more particles for collision, increasing the frequency of successful collisions and therefore increasing the rate. — 2 marks
(d) Uses of catalysts:
(i) Increase the rate of industrial reactions.
(ii) Reduce the energy/cost required for some industrial processes.
(iii) Improve efficiency of production.
Any two = 2 marks
(e) Environmental problems:
(i) Air pollution.
(ii) Water pollution.
(iii) Soil pollution.
(iv) Global warming due to greenhouse gas emissions.
(v) Acid rain.
(vi) Production of toxic waste.
Any two = 2 marks
Total = 16 marks
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