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molecular formula

Need guidance please;

A compound of indium and iodine has the following % composition by mass:

In 23.19%
I 76.81%

Calculate the molecular formula of this compound

Reply 1

amongsttheweeds

Bit rusty so please correct any mistakes. :teehee:

1. Proportion or mass divided by Mr:

In
23.19
----------
114.82
= 0.202

I
76.81
----------
126.90
= 0.605

2. Divide by smallest number (so divide both by 0.202) and round if necessary (sometimes you may have to multiply this by 2, 3, etc. to get two numbers which are close to integers):

In - 1
I - 3

3. Put them together:

InI3 (indium triiodide)

Sometimes the result needs to be multiplied up as it only gives an empirical formula for larger compounds. The method is the same for compounds containing three or more elements, just make sure you divide by the right number.