Al-Nahda Innovative Academy Senior four exams part A

Which of the following gases is commonly described during the fountain experiment using red litmus solution?

• Ammonia

• Hydrogen chloride

• Hydrogen sulphide

• Sulphur trioxide

Answer explanation

Ammonia turns red litmus solution blue while hydrogen sulphide, hydrogen chloride and sulphur trioxide are acidic gases and have no effect on red litmus solution.

Which of the following pairs of compounds will react to form a gas which forms a black solid when bubbled through aqueous potassium iodide solution?

• A. Manganese (iv) oxide and dilute hydrochloric acid

• B. Potassium Manganate (vii) and dilute hydrochloric acid

• C. Bleaching powder and dilute sulphuric acid

• D. Bleaching powder and dilute hydrochloric acid

Answer explanation

Potassium manganate (VII) reacts with dilute hydrochloric acid to form chlorine A B 2KMnO4 (aq) + 16HCl(aq)→ 2KCl (aq) + 2MnCl2 (aq) + 10Cl2 (g) + 8H2O(l)

Chlorine reacts with potassium iodide to produce iodine a black solid Cl2(g) + 2I-(aq) → 2Cl-(aq) + I2(s)

Which of the following oxides does not react with sodium hydroxide solution?

• A. PbO

• B. ZnO

• C. SO2

• D. CO

Answer explanation

A. PbO B. ZnO C. SO2 D. CO PbO, ZnO and SO2 react with sodium hydroxide as shown below PbO (s) + 2NaOH (aq)→ Na2PbO2 (aq) + H2O(l) ZnO (s) + 2NaOH (aq)→ Na2ZnO2 (aq) + H2O(l) SO2(g) + 2NaOH (aq) → Na2SO3 (aq) +H2O(l)

Which of the following ionic compounds can be used as an electrolyte only in molten form?

• A. NaCl

• B. MgCl2

• C. HCl

• D. PbCl2

Propane burns in excess air forming Carbon dioxide gas and water as shown by the equation below. C3H8(g) + 5O2(g) 3CO2(g) +4H2O(l) H=567KJmol-1 The heat produced when 2.7g of propane is burnt in excess air is (C=12, H=1)

• 567/44 * 2.7

• 44/2.7 * 256

• 2.7*567/44

• 44*567/2.7*5

Answer explanation

Formula mass of C3H8 = 12 x 3 + 1 x 8 =44 44g of propane produce 567kJ 2.7g of propane produce

2.7*567/44 kJ

Which of the following allotropes is needle shaped?

• A. Graphite

• B. Monoclinic sulphur

• C. Diamond

• D. Rhombic sulphur

A mixture of sand, sodium chloride and potassium chloride was dissolved in water and then filtered. The components in filtrate can be separated by

• A. filtration

• B. sublimation

• C. fractional distillation

• D. fractional crystallization

Answer explanation

crystallization Fractional crystallization separates salt due to differences in solubility

Which of the following methods can be used to separate a mixture of sodium chloride and ammonium chloride;

• A. Filtration

• B. Sublimation

• C. Decantation

• D. Fractional distillation

Answer explanation

Ammonium chloride sublimes while sodium chloride does not

A hydrocarbon consists of 88.8% carbon by mass; Calculate the empirical formula of the compound. (C = 12, H = 1)

• A. CH₂

• B. C₂H₃

• C. C₄H₈

• D. C₂H₅

Answer explanation

The molarity of a solution containing 2g of sodium hydroxide in 250cm3 of solution is (Na = 23, O = 16, H = 1)

• A. 0.10 M

• B. 0.20 M

• C. 0.05 M

• D. 0.50 M

Answer explanation