# Chemistry 2018 Past Questions | WAEC

Study the following past questions and answers for JAMBWAEC  NECO and Post-JAMB. Get prepared with official past questions and answers for upcoming examinations.

31. When chlorine is passed through a sample of water, the pH of the water sample would be

• A. < 7
• B. > 7
• C. = 7
• D. 0

32.  How many atoms are contained in 0.2moles of nitrogen? $$[N_{A} = 6.02 \times 10^{23}]$$

• A. $$1.20 \times 10^{23}$$
• B. $$2.41 \times 10^{23}$$
• C. $$3.62 \times 10^{23}$$
• D. $$4.82 \times 10^{23}$$

33. The strength of metallic bonds depends on the

• A. charge density of the atoms
• B. ductility of the metal
• C. number of valence electrons
• D. total number of electrons in the atom

34.  When zinc is added to AgNO$$_{3}$$ solution, crystals of silver forms on the zinc surface. This indicates that zinc is

• A. oxidised
• B. reduced
• C. decomposed
• D. dissociated

35.  The empirical formula of a compound containing 0.067mol Cu and 0.066mol O is    [Cu = 63.5, O = 16]

• A. $$Cu_{2}O$$
• B. $$CuO$$
• C. $$CuO_{2}$$
• D. $$CuO_{4}$$

36.  The change in the oxidation state of iron in the reaction represented by the equation:  $$2FeCl_{3} + H_{2}S \to 2FeCl_{2} + 2HCl + S$$  is

• A. +2 to +3
• B. 0 to +2
• C. +3 to +2
• D. +3 to 0

37. Which of the following methods can be used to seperate blood cells from plasma?

• A. Centrifugation
• B. Filtration
• C. Chromatography
• D. Distillation

• A. increases as nuclear charge increases
• B. decreases as nuclear charge increases
• C. decreases as nuclear charge decreases
• D. remains constant as nuclear charge increases

39. Analysis of a hydrocarbon shows that it contains 0.93g of Carbon per gram of the compound. The mole ratio of carbon to hydrogen in the compound is [H = 1.0, C=12.0]

• A. 1:1
• B. 1:2
• C. 2:1
• D. 2:3

40. The law of definite proportions states that

• A. pure samples of the same compound contain the same elements combined in the same proportion by mass
• B. pure samples of substances are in the same proportion by mass
• C. chemical compounds are pure because they contain the same elements
• D. matter can neither be created nor destroyed.

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