Chemical Reactions, Mole Concept & Stoichiometry Quiz

Which pair of elements is most likely to form an ionic compound with each other?

1. Barium, Chlorine
2. Calcium, Sodium
3. Oxygen, Fluorine
4. Sulphur, Carbon

Answer: (a) Barium, Chlorine

In the following question, you will find an assertion and a reason. Select the appropriate option that applies. Assertion (A): Double replacement reactions always produce a precipitate. Reason (R): In a double replacement reaction, two ionic compounds exchange their ions.

1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is false, but R is true.
4. Both A and R are false.

Answer: (c) A is false, but R is true.

During a reaction, aluminium is burnt in chlorine gas to form aluminium chloride. The energy released per mole of aluminium burnt is exceptionally high. - The balanced equation for the reaction is: 2Al(s) + 3Cl2(g) → 2AlCl3(s) - Chlorine gas is a diatomic molecule with weak intermolecular forces but strong covalent bonds. Based on the information, what contributes MOST to the high energy release?

1. Breaking weak covalent bonds in chlorine gas molecules.
2. Formation of strong ionic bonds in AlCl3.
3. Combustion of aluminium to form an oxide layer.
4. Formation of covalent bonds between aluminium and chlorine.

Answer: (b) Formation of strong ionic bonds in AlCl3.

Which of the following correctly represents the Lewis structure for PH3?

Answer: (d)

Which information is most important to determine the empirical formula of a compound?

1. The density of the compound
2. The relative molecular mass of the compound
3. The percentage composition by mass of the compound
4. The volume occupied by 1 mole of the compound

Answer: (c) The percentage composition by mass of the compound

At STP, the volume occupied by 0.5 moles of N2 gas is:

1. 22.4 L
2. 11.2 L
3. 44.8 L
4. 5.6 L

Answer: (b) 11.2 L

A student heats a sample of blue hydrated copper(II) sulphate crystals (CuSO4⋅5H2O) in a lab experiment. The heating drives off the water as water vapour, leaving behind white anhydrous copper(II) sulphate (CuSO4). The student starts with 25.0 g of hydrated copper(II) sulphate and wants to determine the mass of the anhydrous salt left behind. What is the mass of anhydrous copper(II) sulphate (CuSO4) formed after heating? (Molar masses: CuSO4 = 160, H2O = 18)

1. 16.0 g
2. 25.0 g
3. 9.0 g
4. 22.5 g

Answer: (a) 16.0 g

A sample of an unknown compound contains only carbon and hydrogen. If the empirical formula is found to be CH, which of the following best describes what this tells us?

1. The compound must be ethyne (C₂H₂).
2. The empirical formula is the same as the molecular formula in all cases.
3. The compound is hydrogen-rich since CH indicates a high hydrogen percentage.
4. The simplest ratio of C:H is 1:1, but it could be C₂H₂, C₆H₆, or any other multiple.

Answer: (d) The simplest ratio of C:H is 1:1, but it could be C₂H₂, C₆H₆, or any other multiple.

A chemist reacts 8.1 g of aluminium (Al) with 10.65 g of chlorine gas (Cl₂) to produce aluminium chloride (AlCl₃) according to the balanced equation: 2Al + 3Cl2 → 2AlCl3 ​ Given that the molar masses are: Al = 27 g/mol, Cl₂ = 71 g/mol, and AlCl₃ = 133.5 g/mol, which statements are correct? 1. Chlorine gas is the limiting reagent. 2. The theoretical yield of AlCl₃ is 13.35 g. 3. Aluminium is completely consumed in the reaction. 4. The actual yield of AlCl₃ cannot exceed 13.35 g.

1. Only 1 and 2 are correct.
2. Only 1, 2, and 4 are correct.
3. Only 2 and 3 are correct.
4. Only 1 and 4 are correct.

Answer: (b) Only 1, 2, and 4 are correct.

In a reaction, if the theoretical yield of a product is 5.0 g, but the actual yield obtained by the student is 4.0 g, which of the following is true about the scenario? A. The reaction’s efficiency is 80%. B. The limiting reagent must have been used in excess. C. Experimental errors or side reactions may have lowered the actual yield.

1. A only
2. A and B only
3. C only
4. A and C only

Answer: (d) A and C only