Question

How many grams of calcium chloride will be needed to make 750 ml of a 0.100 M CaCl2 solution ?

Answer 1

Molarity or molar concentration is the number of moles of solute that can be dissolved in 1 L of a solution.

Molarity = Number of solute (in moles) / Volume of solution (in liters), or

C = n / V

According to the question,

V = 750 ml and C = 0.100 M

For this, let us convert ml into liters

We know 1 L = 1000 ml

Hence, 750 ml = (750/1000) L = 0.75 L

So, V = 0.75 L

We know that C = n / V

So, n = C x V

n = 0.100 x 0.75 = 0.075

n is the number of moles of solute.

Hence, number of moles of CaCl₂ = 0.075 moles

That means there are 0.075 moles of CaCl₂ in 750 ml of solution.

In order to determine the mass of CaCl₂ in grams, we need to know the molar mass of CaCl₂.

For this, we need to find out the atomic mass of each atom (by referring the periodic table).

CaCl₂ has 1 Ca atom and 2 Cl atoms.

Atomic mass of

Ca = 40.08 g

Cl = 35.45, Cl₂ means 2 x 35.45 = 70.90 g

Adding these values, we get mass of CaCl₂ in grams.

Hence, mass of CaCl₂ = 40.08 + 70.90 = 110.98 g

Thus, 1 mole of CaCl₂ weighs 110.98 g.

Hence, 0.075 moles of CaCl₂ will weigh

0.075 x 110.98 = 8.3235 g, rounded to 8.32 g

So restating the question, we can say that 8.32 grams of CaCl₂ will be needed to make 750 ml of a 0.100 M CaCl₂ solution.