This question might sound dumb but i always had it. When a question gives you a

Question

This question might sound dumb but i always had it. When a question gives you a ratio, how do you know which quantity comes first?

For example in this question:

Silver is composed of two naturally occurring isotopes: Ag107 (51.839%) and Ag109. The ratio of the masses of the two isotopes is 1.0187.

I could easily assume a ratio of Ag-107/Ag-109=1.0187 but would come out with a wrong answer. The ratio they are referring to is Ag-109/Ag-107=1.0187.

So how do you know how to set up the ratio? What prompts you to set it up with Ag-109 on top?

By the way i answered the question already but i got it wrong at the beggining because i asummed Ag-107 on top since it is more abundant.

Explanation / Answer

Note that ratio must always be stated clearly,

if it is not ( your example/question )

then, assume you are doing a division:

Askl yourself, how many times is "B" larger than "A" in comparison

so, if we state "ratio between A and B" is X

B/A = x

B = x*A

this is, how many time will A fit in B

NOTE: it is also pretty common to state the LARGER isotope on top, but this is mostly for nuclear chemistry, if your question is mainly from stoichioemtry, then assume larger isotope on the top

We do this to relate proton/neutron ratio

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