How many milliliters of water must be added to 75.0 mL of 0.150 M AgNO₃ in order to prepare a 0.100 M solution?
(Assume volumes are additive.)

Question

How many milliliters of water must be added to 75.0 mL of 0.150 M AgNO₃ in order to prepare a 0.100 M solution? (Assume volumes are additive.)

Quizplus · Accepted Answer

First, we need to use the dilution formula: 
M1V1 = M2V2 
where M1 is the initial concentration, V1 is the initial volume, M2 is the final concentration, and V2 is the final volume (which includes the initial volume and the volume of water added).

Plugging in the values: 
(0.150 M)(75.0 mL) = (0.100 M)(75.0 mL + V2)

Solving for V2: 
V2 = 37.5 mL

Since we need to add the volume of water, we subtract the initial volume: 
V_water = V2 - V1 = 37.5 mL - 75.0 mL = -37.5 mL

The negative value for V_water means that we need to add 37.5 mL of water. However, we cannot have a negative volume, so we take the absolute value: 
|V_water| = 37.5 mL

Therefore, the best choice is B, 38.0 mL of water (rounded to one decimal place).

How Many Milliliters of Water Must Be Added to 75