WEBVTT

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Here is the problem: 40 mL of 1.5 M solution is diluted to 120 mL. What is the new concentration?

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Diluting adds solvent but not solute, so the moles of solute before and after are equal.

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Moles of solute stay the same when you dilute.

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Rearrange for final concentration M₂.

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Substitute.

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So the answer is final concentration M₂ equals 0.5 M.

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Any volume unit works in M₁V₁ equals M₂V₂ as long as both volumes use the same one. Moles of solute: 0.06 mol.

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M₁V₁ equals 60 and M₂V₂ equals 60, which checks out.