Question

In a group assignment, students are required to fill 10 beakers with 0.720 M CaCl2. If the molar mass of CaCl2 is 110.98 g/mol and each beaker must have 250. mL of solution, what mass of CaCl2 would be used

Answer 1

Answer:

They must weight 199.76 g of Ca$Cl_{2}$ and dilute it in a flask of 2.5 L.

Explanation:

We need to prepare the whole solution and at the end we will slip it in 10 beakers.

Data:

Number of beakers to prepare: 10

Each beaker requires: 250 mL

Total solution volume to prepare = Vt = 10 beakers * 250 mL = 2500 mL = 2.5 L

First step:

We need to use Molarity formula to get amount of solute to weight for the whole solution (Vt = 2.5 L)

Molarity  (M)  formula is:

$M = \frac{mol CaCl_{2} }{Vt}$

where:

M: concentration of the solution expressed in Molarity (mol/L)

mol CaCl2: amount of solute expressed in mol

Vt: total volume of the solution to be prepared. Volume must be expressed in liters (L)

Step 2: Calculate amount of solute

We know concentration of the solution (M = 0.720 M) and also we know total volumen (Vt), then we will despejate mol of CaCl2 (quantity of solute):

$mol CaCl_{2} = M * Vt$

$mol CaCl_{2} = 0.72 M * 2.5 L = 1.8 mol$

Now we need to use molar mass of Ca$Cl_{2}$ (110.98 g/mol) to transform mol of $CaCl_{2}$ in grams of $CaCl_{2}$ :

$gCaCl_{2} = mol CaCl_{2} * \frac{MM}{1 mol CaCl_{2} }$

$gCaCl_{2} = 1.8 mol * \frac{110.98 g}{1 mol} = 199.76 g CaCl_{2}$

Finally, this group of students must weight 199.76 g Ca$Cl_{2}$ and dilute it in a flask of 2.5 L, then they will prepare a solution of Ca$Cl_{2}$ 0.72M.   Then must be placed 250 mL of prepared solution in each beaker.