Question

Suppose that you have to make 775 ml of a 0.5 M solution of sucrose (C12H22O11) in water. Calculate the amount in grams of sucrose needed to make this solution.

The atomic mass of C= 12.01, H= 1.01 and O= 16.00

Round all numbers to the hundredths place during these calculations and in your final answer.

Also descrive the steps involved to make this molar solution.

Answer 1

Required molarity= 0.5 M

Required quantity of solution= 775 ml

Solute is sucrose.

Solvent is water.

Molarity = moles of solute/volume of solvent

Amount of sucrose needed to make 0.5 M solution:

C12H22O11, thus its atomic weight is approximately 342 gmol.

Hence,

1M contains 342 g of sucrose in 1000ml.
So, 0.5 M solution of sucrose will contain
1M= 342 g/1000 ml
0.5 M = 342g/1000ml× 0.5
           = 171g in 1000 ml
As we require only 775 ml solution. Hence, 171/1000ml × 775 ml
              =132.53g

Procedure:
1. Place a magnetic stir bar into a glass beaker on a magnetic stirrer.

2. Weigh out 132.53 g of sucrose into the beaker. This is equivalent to 0.5 moles.

3. Pour 500 mL of water into the beaker.

4. Turn on the magnetic stirrer and allow the solution to mix until all of the sucrose is dissolved.

5. Pour the solution into a 1-liter graduated cylinder, retaining the stir bar in the beaker.

6. Fill the graduated cylinder to the 775-mililiter mark with the remaining water.

7. Pour the solution back into the beaker containing the stir bar and place on the magnetic stirrer for one minute to thoroughly mix.

8. Pour the sucrose solution into a bottle for storage, retaining the magnetic stir bar in the beaker.