Which of the following is consistent with Avogadro’s law?

A.     \(\frac{P}{T} = \) constant (\(V\), \(n\) constant)

B.     \(\frac{V}{T} = \) constant (\(P\), \(n\) constant)

C.     \(Vn = \) constant (\(P\), \(T\) constant)

D.     \(\frac{V}{n} = \) constant (\(P\), \(T\) constant)

D

A number of respondents felt that this question was off-syllabus. This was discussed at length during GA and it was felt that the question itself is clearly on-syllabus as it relates to AS 1.4.4 which states that candidates should be able to apply Avogadro’s law to calculate reacting volumes of gases. In order to apply Avogardo’s law candidates should be able to understand the underlying principle of the law itself. The question was asked within the confines of P1 and a formal definition was not asked, such as could be asked in P2, which in such a case then would be deemed off-syllabus.

The correct answer, D, with \(V{\text{/}}n = \) constant, was given by 40% of candidates and hence it was felt that the question although tough could be answered with a clear understanding of the nature of Avogadro’s law as cited in AS 1.4.4. Some respondents did comment that the law is only valid if \(P\) and \(T\) are constant, which is a fair comment and it would have been better if for each of the answers A-D that the variables for the other constants had been put in brackets.

In the case of the correct answer D, it was assumed that \(P\) and \(T\) are constant and hence as D is the best answer of those given it was decided to keep this question, as 40% of candidates gave D as the correct answer.