Question

21. A student correctly determines that 17.1 grams of sucrose are needed to make 50 mL of a 1 M sucrose solution. When making this solution in lab, the student measured 50 mL of water and massed 17.1 grams of sucrose. The student then mixed the two together into a new beaker. The student's resulting solution was not 1 M sucrose as intended. After the student mixed sucrose and water, the resulting solution was poured into a graduated cylinder and it read 62 mL. a. What part of the molarity equation did the student overlook when mixing the solution? b. What steps should the student take in lab to correctly prepare the 1 M solution?

Answer 1

21)

a)

Molarity = Moles of Solute/Volume of Solution.

Instead of making the volume of solution to be 50 mL, the student took 50 mL solvent (water) which when added with 17.1 g solute (sucrose) made the total volume of solution to be more than 50 mL. Thus, the student overlooked the volume of solute and mistook "volume of solution" for "volume of solvent".

b)

We can prepare a 50 mL solution having concentration 1 M in the following way.

Step 1: We first dissolve completely 17.1 gram sucrose in 10-20 mL water in a beaker.

Step 2: We transfer the solution to graduated cylinder.

Step 3: We add more water to graduated cylinder water to the 50 mL mark, thus making the total volume of solution as 50 mL.