A sample containing , and gives the following elemental analysis: Na 32.08%, O 36.01% and Cl 19.51%. Calculate the mass percent of each compound in the sample.
The relevant molar masses are as follows.
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We assume a sample and can then calculate the mass of as the ratio of to is 1:1, only one compound contains and the mass of is known.
The mass of the remaining two compounds depend on each other. They each share the remaining as well as the of .
From this we get an equation for which depends on .
We can calculate an alternative equation for , referring instead to the remaining .
To simplyfy things a little we can calculate the remaining after has been accounted for.
Which we can now use.
Now we have a system of two equations with two unknowns.
To solve, substitute the first equation into the second.
Then get on one side.
Evaluate.
Put back into the first equation and evaluate.
The percentages, by this method, are as follows.
Which is satisfying because it adds to exactly 100%.
But it is different to the answers in the book.
Alternatively we can derive equations for . First, from .
Second, from the remaining .
Now we have a different system of equations.
To solve.
Yielding this set of percentages.
Mixing the two sets, so we have derived from the remaining and from the , we can get this system.
With this solution.
Yielding this set of percentages.