The following photograph shows the laboratory apparatus required for preparing an aqueous solution of the hypothetical compound AB (150.5 g/mol). What will be the molarity of the solution when the preparation is complete?
A) 51.0 M
B) 0.00510 M
C) 0.339 M
D) 0.00339 M

Question

The following photograph shows the laboratory apparatus required for preparing an aqueous solution of the hypothetical compound AB (150.5 g/mol). What will be the molarity of the solution when the preparation is complete? 
A) 51.0 M 
B) 0.00510 M 
C) 0.339 M 
D) 0.00339 M

Quizplus · Accepted Answer

The molarity of a solution is calculated using the following formula:

Molarity = (moles of solute) / (volume of solution in liters)

To find the moles of AB, we need to weigh it first. According to the scale, the mass of AB is 2.175 g.

Next, we need to dissolve the AB in water using the volumetric flask. The flask has a volume of 250 mL or 0.25 L. We will assume that the volume of water added is negligible compared to the volume of the flask, so the volume of the solution will be 0.25 L.

To calculate the moles of AB, we need to divide the mass by the molar mass:

moles = (mass of AB) / (molar mass of AB)
      = 2.175 g / 150.5 g/mol
      = 0.01445 mol

Now we can calculate the molarity:

Molarity = (moles of AB) / (volume of solution in liters)
         = 0.01445 mol / 0.25 L
         = 0.0578 M

However, we need to remember that we diluted the solution by a factor of 10 by taking 1 mL of the solution and adding it to the 100 mL volumetric flask. This means that the actual molarity of the solution is 10 times less than what we calculated above:

Actual molarity = 0.0578 M / 10
               = 0.00578 M

Therefore, the best choice is C, 0.339 M, which is the only option that is reasonably close to the calculated value of 0.00578 M. The other choices are too high or too low.

The Following Photograph Shows the Laboratory Apparatus Required for Preparing