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Question

What is the concentration of methanol in a solution prepared by combining 8.65mL of a 3.609M methanol solution with 17.70mL of water? Assume volumes are additive and report your answer to 3 decimal places.

Answer 1

This is a dilution problem. The number of moles of methanol is constant, so you can say that M₁V₁ = M₂V₂ where MV is the moles of methanol (concentration time volume) and 1 and 2 are the states before and after diluting with water.

M₂ = M₁(V₁/V₂) which says that the concentration is inversely proportional to Volume that the solution is diluted to. Because Volumes are given to be additive:

M₂ = M₁(V₁/(V₁+V_W)) Note that you don't have to convert ml to liters in this equation.as you usually do when going from molarity to moles. Substitute all terms on the RHS of equation.