FORM FOUR CHEMISTRY NECTA 2021

THE UNITED REPUBLIC OF TANZANIA

NATIONAL EXAMINATIONS COUNCIL OF TANZANIA

CERTIFICATE OF SECONDARY EDUCATION EXAMINATION

032/1                                            CHEMISTRY 1

(For Both School and Private Candidates)

Time: 3 Hours                                                                                         Year : 2021

Instructions

l.     This paper consists of sections A, B and C with a total of fourteen (14) questions.

2.     Answer all questions in sections A and B and one (1) question from section C.

3.    Sections A and C carry fifteen (15) marks each and section B carries seventy (70) marks.

4.    Cellular phones and any unauthorised materials are not allowed in the examination room.

5.     Write your Examination Number on every page of your answer booklet(s).

6.    The following constants may be used.

Atomic masses: H = 1, O =16, C =12, N = 14, Na =23, Ca = 40, Cl = 35.5, Pb= 207.

Avogadro's number =6.02 x 1023 imageGMV at s. t. p 22.4 dm3 .

1 Faraday = 96,500 coulombs.

Standard pressure = 760 mm Hg.

Standard temperature = 273 K.

I litre 1 dm3 1000 cm3image

 

SECTION A ( 15 Marks)

Answer all questions in this section.

l. For each of the items (i) — (x), choose the correct answer from among the given alternatives and write its letter beside the item number in the answer booklet provided.

(i)     Which among the following sets of materials can cause fire outbreak?

A       Oxygen, carbon dioxide and fuel

B        Oxygen, heat and fuel C Oxygen, heat and carbon dioxideimage

D        Oxygen, foam and fuel

E        Oxygen, heat and foam

Choose Answer :


(ii)     What type of fire occurs in vapour air mixture over the surface of flammable liquids?

  1. Class A        
  2. Class B       
  3. Class C
  4. Class D 
  5. Class E
Choose Answer :


(iii)     Which one of the following processes is a chemical change?

A       Butter melts on warm toast

B       Water evaporates from the surface

C       Juice in a bottle freezes

D       Food scrap turns into compost

E       Wet cloth dries

Choose Answer :


(iv)   The simplest formula of a compound formed when combining 36 g of magnesium and 14 g of nitrogen is:

  1. MgN
  2. Mg2N
  3. Mg3N
  4. MgN2
  5. Mg4N2
Choose Answer :


(v)     What is the IUPAC name for H2S04 ?

  1. Sulphuric acid
  2. Sulphuric (VI) acid
  3. Hydrogen sulphate
  4. Dihydrogen sulphate
  5. Hydrogen tetrasulphate
Choose Answer :


(vi)     What type of chemical reaction is represented by the equation 

Zn(s) + 2HCl(aq)  + H2(g)?

A      Displacement reaction

B      Combination reaction

C      Precipitation reaction

D      Decomposition reaction

E       Redox reaction

Choose Answer :


(vii)   What does the random movement of pollen grains suspended in air demonstrates?

A     Matter is lighter in nature.

B      Matter is solid in nature.

C      Matter is particulate in nature.

D      Matter is gaseous in nature. 

      Matter is wave in nature.

Choose Answer :


(viii)   "Organic matter is among the components of soil." Which role does it play?

A    Improving water infiltration of the soil.

B    Accelerating break down of organic matter.

C     Reserving nutrients thus providing soil fertility.

D     Converting of nitrogen into nitrates.

E     Providing a room for organic material such as nylons.

Choose Answer :


(ix)   Which of the following sets represents isotopes of an element?

A.      Z, and 

B.    Z, and 

C.    Z, and 

D.   Z, and 

E.  Z, and 

Choose Answer :


 (x)     What is to be considered when choosing the best method to extract a particular metal from its ore?

A    The metal 's economic value.

B     Its availability in an area.

C    The metal's ore impurities.

D    How it reacts with other materials. 

E    The metal's shininess.

Choose Answer :


2.   Match the uses of First Aid Kit items in List A with the respective items in List B by writing the letter of the correct response besides the item number in the answer booklet provided.

List A

List B

  1. Washing out foreign particles from eye and cleaning wounds.
  2. Cleaning wounds to kill germs and bacteria.
  3.                     Preventing the skin from moisture loss through evaporation
  4.                      Treating fungal infections
  5. Washing hands, wounds and equipments
  1. Antiseptic
  2. Detergent
  3. Gentian violet
  4. Iodine tincture
  5. Petroleum jelly
  6. Saline
  7. Sterile gauze
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Qn. Here...View Ans


SECTION B ( 70 Marks)

imageAnswer all questions in this section.

3.   (a) Different salts behave differently when heated. Use balanced chemical equations to show how carbonates and sulphates behave when subjected to heat.

(b)   Ammonium nitrate does not react like other nitrates (with exception of the alkali metal nitrates). Explain this fact with the aid of chemical equations. (7 marks)

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4.    (a)   A Form IV student was asked to react phosphate ion and sodium ion forming compound W. Suggest the IUPAC name of W and find the oxidation state of phosphorous in W.

(b)   Calculate the percentage composition of lead in the compound Pb(N03)2. (7 marks)

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5.   (a) How can the society minimize the energy loss encountered in the use of charcoal and fire wood? Give two points.

(b)   State whether the following processes are exothermic or endothermic.

(i)    Dissolving ammonium chloride in water.

(ii)     Photosynthesis.

(iii)     Combustion reactions.

(iv)     Mixing water and potassium chloride.

(v)        Mixing water and strong acids such as concentrated sulphuric acid.

(7 marks)

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6.   (a)    Briefly explain the concept of scientific procedure.

(b)   What is the importance of the scientific procedure in daily life? Give two points.(7 marks)

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7.   Use the following components to construct a diagram of water cycle: clouds, animal, water in the soil, rain, plants, water spring, rivers, lakes and water vapour in the atmosphere.(7 marks)

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8.    Suppose that two gas jars; one containing gas "A" and another one containing gas "B" are made available to you. Gas "A" is used in hardening of margarine whereas gas "B" is used by mountain climbers.

(a)    What tests will you conduct to identify each of the two gases?

(b)    Give two physical properties and three chemical properties that can be used to distinguish gas "A" from gas "B".      (7 marks)

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9.               Two experiments A and B were conducted to prepare hydrogen gas by varying the size of zinc granules which were reacted with dilute hydrochloric acid. All other factors were kept constant in the two experiments. Data obtained were used to plot the following graph: image

image

Time

(a)            Briefly explain the differences in the results of experiments A and B.

(b)            What factors can be adjusted to increase the yield of the product?      (7 marks)

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10.   If 2.0 g of CaC03 were reacted with excess dilute HCI acid; (a) what volume of C02 would be given out at s.t.p?

(b)    Calculate the mass of C02 produced.   (7 marks)

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11.   (a)  In three points, differentiate homogenous mixtures from heterogeneous mixtures.

(b)    By giving four points, justify the fact that common salt is a compound. (7 marks)

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12.   (a)    Give three ways in which environmental destruction is likely to occur during extraction of metals.

(b)   The following equations represent the steps involved in the conversion stages of iron extraction in Bussener converter. Arrange the equations in chronological order from the first step to the last by writing the respective letter so as to get a complete explanation of the conversion stage.

   V: 2Cu20(S) +   Cu2S(S)→     6Cu (l) + S02 (g)

  W:  FeO (l) + SiO2(g) → FeSiO3

   X: 2Cus(s) +302 (g)           2Cu20(s) +2S02 (g)

   Y: 2FeS (l) +302 (g) → 2Feo(1) + 2S02 (g)                                          (7 marks)image

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SECTION C (  15 Marks)

Answer one (1) question from this section.

13.    By giving six points, explain how to maintain soil fertility of a particular area.(15 marks)

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14.     How electrolysis is applied in industries? Describe by giving six points.  (15 marks

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