Question

Calculate the mass (in grams) of methylene bluecrystals that you must weigh in order to make 100.0mL of 1.25 × 10-5mol/L methylene

Answer 1

Answer: The mass of methylene blue that must be weighed is $3.99\times 10^{-4}g$

Explanation:

To calculate the mass of solute, we use the equation used to calculate the molarity of solution:

$\text{Molarity of the solution}=\frac{\text{Mass of solute}\times 1000}{\text{Molar mass of solute}\times \text{Volume of solution (in mL)}}$

We are given:

Molarity of solution = $1.25\times 10^{-5}M$

Molar mass of methylene blue = 319.85 g/mol

Volume of solution = 100.0 mL

Putting values in above equation, we get:

$1.25\times 10^{-5}M=\frac{\text{Mass of methylene blue}\times 1000}{319.85\times 100.0}\\\\\text{Mass of methylene blue}=\frac{1.25\times 10^{-5}\times 319.85\times 100.0}{1000}=3.99\times 10^{-4}g$

Hence, the mass of methylene blue that must be weighed is $3.99\times 10^{-4}g$