Question

how much ethylene glycol needs to be weighed out to make a 0.500 m solution using a 250.0 ml flask?

Explanation:

Step1: Calculate the number of moles of ethylene glycol

The formula for molarity \(M=\frac{n}{V}\), where \(M\) is molarity, \(n\) is the number of moles, and \(V\) is the volume in liters.
Given \(M = 0.500\space M\) and \(V=250.0\space mL=0.2500\space L\)

$$n = M\times V$$

$$n=0.500\space mol/L\times0.2500\space L = 0.125\space mol$$

Step2: Calculate the mass of ethylene glycol

The molar mass of ethylene glycol \((C_2H_6O_2)\) is \(M_{r}=(2\times12.01)+(6\times1.008)+(2\times16.00)=62.07\space g/mol\)
The formula for mass \(m=n\times M\) (where \(n\) is the number of moles and \(M\) is the molar mass)

$$m = 0.125\space mol\times62.07\space g/mol=7.76\space g$$

Answer:

\(7.76\space g\)