Question

When 74 grams of ${Ca\left(OH\right)}_2$ is dissolved in 2 liters of water. What is concentration of a solution?

• A. 25 molar
• B. 1 molal
• C. 1 molar
• D. .5 molal
• E. 0.5 molar

Answer 1

The correct option is E 0.5 molar

When 74 grams of $Ca(OH{)}_2$ is dissolved in 2 liters of water. The concentration of a solution is 0.5 molar.
The molar mass of $Ca(OH{)}_2=40.1+2\times (16+1)=74.1g/mol$
Number of moles of $Ca(OH{)}_2=\frac{74g}{74.1g/mol}=1mole$
Molarity of solution is the ratio of the number of moles of $Ca(OH{)}_2$ present in 1 L of solution.
Molarity $=\frac{1}{2}=0.5M$