Stoichometery Problem

Question

how many milliliters of concentrated 15 M ammonia would you use to make 500 ml of 6 M NH3?

Answer 1

This involves dilution. Formula is M₁V₁ = M₂V₂

M₁ = 15 M V₁ = ? M₂ = 6 M V₂ = 500 mL

Rearrange formula, to get V₁ = M₂V₂ / M₁ (6 X 500) / 15 = 200 mL

So you would pour 200 mL of 15 M NH₃ into a flask, and add enough water to bring it up to 500 mL, in this case you would add 300 mL of water. In your calculation, you could go through the point of dividing the volume of V₂ by a 1000 mL = 1 L, but then the 1000 mL = 1 L gets cancelled back out when you find the V₁, so just as easy to use just plug in the numbers as long as you make your answer's volume the same unit as your given amount. The reason you may want to consider the 1000 mL = 1 L part of the conversion is the fact that Molarity is defined as mol / L, but as pointed out above, it is a little redundant at this point.