Questions: If 42 grams of sodium hydroxide is dissolved in enough water to make a 0.75 L solution. What is the resulting molar concentration?

Solution Steps

First, we need to determine the number of moles of sodium hydroxide (NaOH). The molar mass of NaOH is calculated as follows:

• Sodium (Na): 22.9898 g/mol
• Oxygen (O): 15.9994 g/mol
• Hydrogen (H): 1.0079 g/mol

So, the molar mass of NaOH is: \[ 22.9898 + 15.9994 + 1.0079 = 39.9971 \, \text{g/mol} \]

Next, we use the formula to find the number of moles: \[ \text{moles of NaOH} = \frac{\text{mass of NaOH}}{\text{molar mass of NaOH}} = \frac{42 \, \text{g}}{39.9971 \, \text{g/mol}} = 1.0501 \, \text{mol} \]

The molar concentration (M) is given by the number of moles of solute divided by the volume of the solution in liters: \[ \text{Molar concentration} = \frac{\text{moles of NaOH}}{\text{volume of solution in liters}} = \frac{1.0501 \, \text{mol}}{0.75 \, \text{L}} = 1.4001 \, \text{M} \]

Final Answer