A solution of NaOH (molar mass 40g/mol) was prepared by dissolving 1.6g of NaOH in ${500 cm}^{3}$ water. Calculate the molarity of the NaOH solution?

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NaOH = 0.18M

NaOH = 0.08M

NaOH = 0.2M

NaOH = 0.06M

answer is B.

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Detailed Solution

Molarity(M) =

\frac{n}{V (ml)} \times 1000

Where n = moles of solute
V = volume of solution in ml
The solution in this problem is NaOH, while the solution is water.
Let's figure out how many moles of NaOH there are.

n_{NaOH} = \frac{weight of NaOH}{molar mass of NaOH}

Weight of NaOH(given) = 1.6 g
Molar mass of NaO = 40 g/mole
Substitute a number of moles of NaOH for the quantities in the given formula.

n_{NaOH} = \frac{weight of NaOH}{molar mass of NaOH}

{= \frac{1.6 g}{40 g / mol} = 0.04 moles}_{}

Given volume of solution

{= 500 cm}^{3} =

volume of water = 500 mL
In the molarity formula above, replace the number of moles of NaOH with the amount of water.
Then,

{M = \frac{0.04 moles}{50 mL} \times 1000 = 0.08 moles / L}_{}

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