In: Chemistry
Provide 3 different approaches [a. Using mass % values; b. using the formula as a conversion factor (moles F and moles Ca) and c. law of definite proportions (grams F and grams Ca)] to solving the following: Calculate the number of grams of fluorine in a sample of calcium fluoride that contains 2.01 g of calcium. Answer: 1.91 g F
a)
calcium fluoride is CaF2
mass % of Ca = molar mass of Ca*100 / molar mass of
CaF2
= 40*100/78
= 51.3 %
mass % of F = 100 - 51.3 = 48.7 %
use:
mass % of Ca = mass of Ca*100 / total mass
51.3 = 2.01 * 100 / total mass
total mass = 3.92 g
To find mass of F use:
mass % of F= mass of F*100 / total mass
48.7 = mass of F * 100 / 3.92
mass of F = 1.91 g
Answer: 1.91 g
b)
Mass of Ca = 2.01 g
Molar mass of Ca = 40 g/mol
number of moles of Ca = mass / molar mass
= 2.01/40
= 0.05025 mol
In CaF2, 1 mol of Ca needs 2 mol of F
So, 0.05 mol Ca will need 0.05025*2 = 0.105 mol of F
Molar mass of F = 19 g/mol
Mass of F = molar mass of F * number of moles
= 19 * 0.105
=1.91 g
Answer: 1.91 g
c)
Ca and F reacts in 1:2 proportion
proportion of Ca= 1/2 * moles of F
mass of Ca / molar mass of Ca = mass of F/molar mass of F
2.01/40 = mass of F / 19
mass of F = 1.91 g
Answer: 1.91 g