How many molecules are present in a drop of ethanol, ${{\text{C}}_{\text{2}}}{{\text{H}}_{\text{5}}}{\text{OH}}$, of mass $2.3 \times {10^{ - 3}}{\text{ g}}$? $({{L}} = 6.0 \times {10^{23}}{\text{ mo}}{{\text{l}}^{ - 1}})$

A.     $3.0 \times {10^{19}}$

B.     $3.0 \times {10^{20}}$

C.     $6.0 \times {10^{20}}$

D.     $6.0 \times {10^{26}}$

A

Some respondents stated that the numbers could have been more user-friendly in these questions, as candidates do not have access to a calculator in P1. This is a fair comment which will be borne in mind for future paper-setting. Candidates found Q3 particularly challenging with only 35.79% of candidates getting the correct answer A. The inconsistent use of significant figures in Q2 was also commented on, equally a valid comment. One respondent stated that they found the use of ${\text{d}}{{\text{m}}^{\text{3}}}$ instead of L confusing for North American candidates. However on IB Chemistry papers the unit of ${\text{d}}{{\text{m}}^{\text{3}}}$ for volume is always used instead of L and candidates should be prepared for this.