WEBVTT

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Here is the problem: 7.455 g of KCl is dissolved in water to make 500 mL of solution. What is the molarity?

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Molarity is moles of solute per litre of solution.

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Molar mass of KCl.

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Convert grams to moles.

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Convert the volume to litres.

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Molarity is moles per litre.

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So the answer is M equals 0.200005 mol/L.

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Molarity (mol/L, written M) uses the volume of the whole solution, not of the solvent alone. To make a solution, weigh the solute, dissolve it in less solvent, then top up to the final volume.

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n equals MV: 0.200005 times 0.5 equals 0.100003 mol, which checks out.