1. The neutral atoms of all isotopes of the same element have
Different number of protons
Equal number of neutrons
The same number of electrons
The same mass number
(c) Isotopes of the same element have the same number of protons and electrons, but different numbers of neutrons. The atomic number (number of protons) defines the element.
2. The number of fundamental particles in an atom of the lightest isotope of carbon are
6
12
18
24
(c) The lightest isotope of carbon is C-12, which has 6 protons, 6 neutrons, and 6 electrons, totaling 18 fundamental particles.
3. A pressure vessel contains a gaseous mixture made up of 2.34 kg silane, SiH₄ and 55.4 kg argon. Determine the mole fraction of silane
0.050
0.041
0.095
0.064
(a) Moles of SiH₄ = 2.34/32 = 0.0731 mol; Moles of Ar = 55.4/40 = 1.385 mol; Total moles = 1.4581 mol; Mole fraction of SiH₄ = 0.0731/1.4581 = 0.0501 ≈ 0.050
4. 138 grams of ethyl alcohol is mixed with 72 grams of water. The ratio of number of moles of alcohol to water is
3:1
3:2
1:3
3:4
(d) Moles of ethyl alcohol (C₂H₅OH, MW=46) = 138/46 = 3 mol; Moles of water (H₂O, MW=18) = 72/18 = 4 mol; Ratio = 3:4
5. Which one of the following is a covalent crystal?
Dry ice
Rock salt
Ice
Quartz
(d) Quartz (SiO₂) is a covalent crystal with Si-O covalent bonds throughout. Dry ice and ice are molecular crystals, while rock salt is an ionic crystal.
6. An ionic compound has a unit cell consisting of A ions at the corners of a cube and B ions on the centres of faces of the cube. The empirical formula of the compound would be
AB
A₂B
AB₂
AB₃
(c) A ions at corners: 8 corners × 1/8 = 1 A ion; B ions at face centers: 6 faces × 1/2 = 3 B ions. Therefore, the formula is AB₃.
7. There are _____ molecules of gas in one dm³ at STP
2.69×10²²
6.02×10²³
3.07×10²³
2.07×10²³
(a) At STP, 1 mole of gas occupies 22.4 L. In 1 dm³ (1 L), there are (1/22.4) × 6.022×10²³ = 2.69×10²² molecules.
8. If 5.0 g of each reactant were used for the following process, the limiting reactant would be: 2KMnO₄+5Hg₂Cl₂+16HCl→10HgCl₂+2MnCl₂+KCl+8H₂O
KMnO₄
HCl
H₂O
Hg₂Cl₂
(a) Calculate moles of each reactant from 5.0 g. KMnO₄ has the highest molecular weight (158 g/mol), giving the fewest moles, making it the limiting reactant.
9. Na⁺ is isoelectronic with
Ca²⁺
Mg²⁺
Zn²⁺
Cu²⁺
(b) Na⁺ has 10 electrons (11-1). Mg²⁺ also has 10 electrons (12-2). Both have the same electron configuration as neon.
10. Compounds with an oxygen atom bonded to two organic groups are known as
Ethers
Hydroxides
Hydrolysis
Phenols
(a) Ethers have the general formula R-O-R', where an oxygen atom is bonded to two organic groups (alkyl or aryl groups).
11. What is the major product of the following reaction? CH₂=CH−CH₂−OH →[HBr, Peroxide]
CH₃−CHBr−CH₂−OH
CH₃−CHBr−CH₂−Br
BrCH₂−CH₂−CH₂−OH
CH₃−CH(OH)−CH₂−OH
(c) In the presence of peroxides, HBr addition follows anti-Markovnikov's rule due to free radical mechanism, giving BrCH₂−CH₂−CH₂−OH.
12. Which is the most suitable reagent for the following conversion? CH₃−CH=CH−CH₂−CO−CH₃→CH₃−CH=CH−CH₂−CO−OH
Tollen's reagent
Benzyl peroxide
I₂ and NaOH solution
Sn and NaOH solution
(c) The iodoform reaction (I₂ + NaOH) oxidizes methyl ketones to carboxylic acids, converting −CO−CH₃ to −CO−OH.
13. An unknown compound is insoluble in water but dissolves in sodium bicarbonate with a release of CO₂ bubbles. The compound is almost certainly:
An aldehyde
A carboxylic acid
An amine
An alcohol
(b) Carboxylic acids react with NaHCO₃ to produce CO₂: RCOOH + NaHCO₃ → RCOONa + H₂O + CO₂. This is a characteristic test for carboxylic acids.
14. Amines have basic properties because of the presence of
A hydroxyl group in such compounds
A lone pair of electrons on the nitrogen atom
A negative charge on the hydrogen atom attached to nitrogen
Hydrogen atoms on the nitrogen atom that are easily dissociated
(b) Amines are basic because the nitrogen atom has a lone pair of electrons that can accept a proton (H⁺), acting as a Lewis base.
15. Aromatic molecules contain n electrons.
4n+1 (with n an integer)
Unpaired
4n+2 (with n an integer)
4n (with n an integer)
(c) According to Hückel's rule, aromatic compounds contain (4n+2) π electrons, where n is a non-negative integer (0, 1, 2, 3...).
16. In DNA the complementary bases are:
Adenine and thymine, guanine and cytosine
Uracil and adenine, cytosine and guanine
Adenine and guanine, thymine and cytosine
Adenine and thymine, guanine and uracil
(a) In DNA, adenine (A) pairs with thymine (T) via two hydrogen bonds, and guanine (G) pairs with cytosine (C) via three hydrogen bonds.
17. Terylene is a condensation polymer of ethylene glycol and
Benzoic acid
Phthalic acid
Terephthalic acid
Salicylic acid
(c) Terylene (polyethylene terephthalate, PET) is formed by condensation polymerization between ethylene glycol and terephthalic acid.
18. P-acetamidophenol is an
Antibiotic
Anesthetic
Antiseptic
Antipyretic
(d) P-acetamidophenol is paracetamol (acetaminophen), which is commonly used as an antipyretic (fever reducer) and analgesic (pain reliever).
19. Smelting is carried out in
Blast furnace
Muffle furnace
Open hearth furnace
Electric furnace
(a) Smelting, the process of extracting metals from their ores by heating and melting, is typically carried out in blast furnaces, especially for iron extraction.
20. A powdered ore is fused with Na₂CO₃ and the fused mass extracted with water. In the clear extract, CO₂ gas is passed when a white precipitate is obtained. The ore can be
Magnesite
Bauxite
Magnetite
Malachite
(b) This describes the test for aluminum in bauxite. Al₂O₃ fuses with Na₂CO₃ to form sodium aluminate, which precipitates as Al(OH)₃ when CO₂ is passed through the solution.
