To determine the molarity of a potassium hydroxide ([tex]\( KOH \)[/tex]) solution given the volume and mass of [tex]\( KOH \)[/tex], follow these steps:
1. Convert the volume of the solution from milliliters (mL) to liters (L):
Given the volume of the solution is [tex]\( 50 \, \text{mL} \)[/tex].
Convert it to liters:
[tex]\[
50 \, \text{mL} \times \frac{1 \, \text{L}}{1000 \, \text{mL}} = 0.05 \, \text{L}
\][/tex]
2. Calculate the molar mass of potassium hydroxide ([tex]\( KOH \)[/tex]):
The given atomic masses are:
[tex]\[
K = 39, \quad O = 16, \quad H = 1
\][/tex]
The molar mass of [tex]\( KOH \)[/tex] combines these atomic masses:
[tex]\[
\text{Molar mass of } KOH = 39 + 16 + 1 = 56 \, \text{g/mol}
\][/tex]
3. Calculate the number of moles of [tex]\( KOH \)[/tex]:
Given the mass of [tex]\( KOH \)[/tex] is [tex]\( 7 \, \text{g} \)[/tex].
Use the molar mass to find the moles:
[tex]\[
\text{Moles of } KOH = \frac{\text{mass of } KOH}{\text{molar mass of } KOH} = \frac{7 \, \text{g}}{56 \, \text{g/mol}} = 0.125 \, \text{mol}
\][/tex]
4. Calculate the molarity of the solution:
Molarity ([tex]\( M \)[/tex]) is defined as the number of moles of solute per liter of solution:
[tex]\[
\text{Molarity} = \frac{\text{moles of solute}}{\text{volume of solution in liters}} = \frac{0.125 \, \text{mol}}{0.05 \, \text{L}} = 2.5 \, \text{mol/L}
\][/tex]
Thus, the molarity of the potassium hydroxide solution is [tex]\( 2.50 \, \text{mol/L} \)[/tex].
The correct answer is: B. 2.50
