Question

How many moles of potassium hydroxide (KOH) are dissolved in 250 mL of a 0.15-M KOH solution?

Accepted Answer

Molarity or M is a unit of concentration and is the ratio of number of moles to the volume of the solution (in liters). 
That is, molarity = number of moles / volume of solution
Here, the volume of solution is given as 250 ml. There are 1000 ml in a liter of a solution. Therefore the volume of solution is 250 ml/1000 L = 0.25 L.
The molarity of the solution is 0.15 M.
Thus, 0.15 = number of moles / 0.25 L
or, number of moles = 0.15 mol/L x 0.25 L = 0.0375 moles.
Thus, there are 0.0375 moles of potassium hydroxide in the solution when we have 250 mL of 0.15 M solution.
Since the molar mass of potassium hydroxide is 56.1 g, we have 2.1 g (0.0375 moles x 56.1 g/mole) of potassium hydroxide.
Hope this helps.

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How many moles of potassium hydroxide (KOH) are dissolved in 250 mL of a 0.15-M KOH solution?

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