Question

How many grams of Ca(OH)2 are need to make 100 ml of a 100mM solution? (numbers only, to nearest 0.01)

Answer 1

Answer:

0.74 grams

Explanations

Given the following parameters

Volume of Ca(OH)₂ = 100mL = 0.1L

Molarity of Ca(OH)₂ = 100mM = 0.1M

Determine the moles of Ca(OH)₂

$\begin{gathered} moles\text{ of Ca\lparen OH\rparen}_₂=molarity\times volume \\ moles\text{ of Ca\lparen OH\rparen}_₂=\frac{0.1mol}{L}\times0.1L \\ moles\text{ of Ca\lparen OH\rparen^^^^2082=0.01mole} \end{gathered}$

Calculate the mass of Ca(OH)₂

Molar mass of Ca(OH)2 = 20 + (16*2) + (2*1.01)

Molar mass of Ca(OH)2 = 40 +32 + 2.02

Molar mass of Ca(OH)2 = 74.02g/mol

$\begin{gathered} Mass\text{ of Ca\lparen OH\rparen}_2=moles\times molar\text{ mass} \\ \text{Mass of Ca\lparen OH\rparen}__2=0.01mole\times74.02\frac{g}{mole} \\ Mass\text{ of Ca\lparen OH\rparen}_2\approx0.74grams \end{gathered}$

Hence the amount of mass of Ca(OH)2 needed to make 100 ml of a 100mM solution is 0.74 grams