DP Chemistry (first assessment 2025)
Question 19M.2.SL.TZ2.5b(iii)
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.SL.TZ2.5b(iii) |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Identify | Question number | b(iii) | Adapted from | N/A |
b(iii).
[Maximum mark: 2]
19M.2.SL.TZ2.5b(iii)
(b(iii))
Identify the type of bonding in sodium hydrogencarbonate.
Between sodium and hydrogencarbonate:
Between hydrogen and oxygen in hydrogencarbonate:
[2]
Markscheme
Between sodium and hydrogencarbonate:
ionic [✔]
Between hydrogen and oxygen in hydrogencarbonate:
«polar» covalent [✔]
Examiners report
Many candidates identified the bonding between sodium and hydrogencarbonate as ionic. A much smaller proportion of candidates identified the bonding between hydrogen and oxygen in hydrogencarbonate as covalent. The most common mistake was “hydrogen bonding”.
Syllabus sections
Structure 2. Models of bonding and structure » Structure 2.2—The covalent model » Structure 2.2.1—A covalent bond is formed by the electrostatic attraction between a shared pair of electrons and the positively charged nuclei. The octet rule refers to the tendency of atoms to gain a valence shell with a total of 8 electrons. Deduce the Lewis formula of molecules and ions for up to four electron pairs on each atom.
Structure 2. Models of bonding and structure » Structure 2.1—The ionic model » Structure 2.1.2—The ionic bond is formed by electrostatic attractions between oppositely charged ions. Deduce the formula and name of an ionic compound from its component ions, including polyatomic ions. Binary ionic compounds are named with the cation first, followed by the anion. The anion adopts the suffix “ide”. Interconvert names and formulas of binary ionic compounds.