10 questions. Try each one, then open the answer to check yourself and read the explanation.
Which of the following elements has the highest electronegativity?
Answer: C (fluorine)
Fluorine is the most electronegative element (3.98 on the Pauling scale), higher than oxygen (3.44) and chlorine (3.16).
What is the shape of methane molecule?
Answer: B (tetrahedral)
Carbon in CH4 has four bonding pairs, which spread out as far as possible into a tetrahedral shape (bond angle 109.5°).
The rate of a chemical reaction can be increased by
Answer: D (two of the above)
Both raising the temperature and adding a catalyst speed up a reaction; lowering the concentration slows it. So 'two of the above' is right.
What is the molecular formula of a compound that contains 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass? Take the relative molecular mass of the compound as 180 (C = 12, H = 1, O = 16)
Answer: C (C6H12O6)
Mole ratio C : H : O = 40/12 : 6.7/1 : 53.3/16 = 3.33 : 6.7 : 3.33 = 1 : 2 : 1, so the empirical formula is CH2O (mass 30). 180 ÷ 30 = 6, giving C6H12O6.
The process by which a gas changes directly to a solid is called
Answer: C (deposition)
Gas turning straight into solid is deposition. Sublimation is the reverse (solid straight to gas) and condensation is gas to liquid.
What is the main component of natural gas?
Answer: D (methane)
Natural gas is mostly methane (about 70-90%), with smaller amounts of ethane, propane and butane.
The principle that states that no two electrons in an atom can have the same set of four quantum numbers is
Answer: A (Pauli Exclusion principle)
The Pauli exclusion principle says no two electrons in an atom share all four quantum numbers, so an orbital holds at most two electrons of opposite spin.
Which of the following is the best conductor of electricity?
Answer: B (graphite)
In graphite each carbon uses only three electrons for bonding; the fourth is delocalised and free to carry current. Diamond and sulphur are insulators and silicon is only a semiconductor.
How many molecules are there in 11.2dm3 of ammonia at s.t.p? (G.M.V = 22.4dm3 at stp, NA = 6.02 × 1023mol−1)
Answer: D (3 × 1023)
Moles = 11.2 ÷ 22.4 = 0.5 mol. Molecules = 0.5 × 6.02 × 1023 ≈ 3 × 1023.
What is the electronic configuration of chloride ion (Cl−)?
Answer: B (1s22s22p63s23p6)
Chlorine (17 electrons) ends in 3p5; the chloride ion gains one electron, giving 18 electrons ending in 3p6.