Chemistry Fundamentals Flashcards

What is the shape and bond angle of a methane (CH₄) molecule?

Answer: Tetrahedral, 109.5°

Methane has four bonding pairs of electrons around the central carbon atom with no lone pairs, giving a tetrahedral shape with bond angles of 109.5° as predicted by VSEPR theory.

Which of the following best describes an ionic bond?

Answer: Electrostatic attraction between oppositely charged ions formed by electron transfer

Ionic bonding involves the transfer of electrons from a metal to a non-metal, creating positively and negatively charged ions held together by strong electrostatic attraction in a giant ionic lattice.

In a titration, 25.0 cm³ of 0.100 mol dm⁻³ NaOH is exactly neutralised by HCl. If 20.0 cm³ of HCl was used, what is its concentration?

Answer: 0.125 mol dm⁻³

Moles of NaOH = 0.025 × 0.100 = 0.0025 mol. NaOH:HCl ratio is 1:1, so moles of HCl = 0.0025. Concentration = 0.0025 / 0.020 = 0.125 mol dm⁻³.

What is the oxidation state of manganese in the permanganate ion MnO₄⁻?

Answer: +7

Each oxygen is -2, giving 4 × (-2) = -8. The overall charge is -1. So Mn + (-8) = -1, therefore Mn = +7. Permanganate is a powerful oxidising agent due to this high oxidation state.

Which of the following molecules exhibits hydrogen bonding?

Answer: HF

Hydrogen bonding requires hydrogen bonded to a highly electronegative atom (F, O, or N). HF fits this criterion as fluorine is the most electronegative element. H₂S and PH₃ only have weaker van der Waals forces as S and P are not sufficiently electronegative.

What is the empirical formula of a compound containing 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?

Answer: CH₂O

Dividing by atomic masses: C = 40.0/12 = 3.33, H = 6.7/1 = 6.7, O = 53.3/16 = 3.33. Ratio = 1:2:1, giving empirical formula CH₂O.