Question

Two elements, R and Q, combine to form two binary compounds. In the first compound, 14.0 g of R combines with 3.00 g of Q. In the second compound, 7.00 g of R combines with 4.50 g of Q. If the formula of the second compound is RQ3, what is the formula of the first compound?

Answer 1

The formula of the first compound is RQ

Step-by-step explanation:

Chemical formula is the simplest whole number ratio of moles of each element in the compound.

To determine the formula of a compound we must know the molar mass of each element (How many grams weighs a mole of the compound).

The formula of the second compound is RQ₃. That is 1 mole of R and 3 moles of Q.

1 mole of R weighs 7.00g. That means its molar mass is 7g/mol.

3 moles of Q weighs 4.50g. Its molar mass is 4.50g / 3 moles: 1.50g/mol

In the first compound, there are 14.0g = 2 moles of R

And 3.00g of Q = 2 moles of Q.

And you can think formula is:

R₂Q₂

But, as formula is the simplest whole number ratio,

The formula of the first compound is RQ