Question

A 5.29 g mixture contains both lithium fluoride, LiF, and potassium fluoride, KF. If the mixture contains 3.17 g fluorine, what is the mass of the KF in the mixture?

mass of KF:

Answer 1

By setting up a mass ratio and solving an algebraic equation where the mass of KF is denoted by x, we find that the mass of KF in the mixture is approximately 1.98 grams.

Step-by-step explanation:

To determine the mass of KF in the mixture, we need to subtract the mass of the fluorine from the total mass of the mixture. First, we determine the mass of the lithium fluoride (LiF) in the mixture as follows:

• The molar mass of LiF (6.94 + 19.00) is approximately 25.94 g/mol.
• The molar mass of KF (39.10 + 19.00) is approximately 58.10 g/mol.
• Each mole of LiF or KF contains one mole of fluorine, which has a mass of approximately 19.00 g/mol.

We have 3.17 g of fluorine in the mixture. To find out how much of this fluorine comes from LiF or KF, we can set up a ratio.

Let's call the mass of KF x and the mass of LiF (5.29 - x) grams.

So, the mass of F from KF is (x / 58.10) * 19.00 and from LiF it is ((5.29 - x) / 25.94) * 19.00. The sum of both will equal 3.17 g:

(x / 58.10 * 19.00) + ((5.29 - x) / 25.94 * 19.00)

= 3.17

Solving this equation for x, we can find the mass of the KF in the mixture. Using algebra:

x ≈ 1.98 g.

Therefore, the mass of the KF in the mixture is approximately 1.98 grams.