Question

The following question was posed on an exam:

Answer 1

Answer:

The answer given by the student is not totally correct.

Explanation:

Law of multiple proportions states that an element Q will react with different volume of Fluorine to produce two non-similar compounds. Hence, the ratio of the masses(Fluorine only) needs to be an absolute reduced value.

Given that:

3.2 g of a sample of Q reacts with Fluorine to form 10.8 g of the unknown fluoride A.

This means the mass of Fluorine present in the compound = 10.8 g - 3.2 g = 7.6 g

Thus, 3.2 g of a sample of Q reacts with 7.6 g of Fluorine.

Also, 6.4 g sample of Q reacts with Fluorine to form 29.2 g of unknown fluoride B.

If we divide the samples by (2), we have 3.2 g sample of Q reacting with Fluorine to form 14.6 g of unknown fluoride B.

This means the mass of Fluorine present in the compound = 14.6 g - 3.2 g = 11.4 g

Thus, 3.2 g Q reacted here with 11.4 g fluorine.

Hence, 11.4/7.6 = 1.5 = 3/2

This above therefore satisfies the law of multiple proportions.

This is not aligned with what the student did, what the student did was to relate the amount of Q used to make A and B. Suppose, we start with twice amount of Q, the ratio would have been smaller(i.e. the ratio of Q).

So, this doesn't relate to the law of multiple proportions.

The law of multiple proportions is specifically concerned with the mass of the element rather than Q that can react with Q. Therefore, there is more reason to relate the two samples of equal masses of Q that react with different masses of Fluorine. The ratios of Fluorine will then be small whole numbers.