SCH3U Lab 4.2 Name:______

Preparation of Solutions: Creating A Liquid Rainbow

Introduction

What do the effectiveness of a medicine, the safety of a chemical reaction, and the cost of an industrial process have in common? They all depend on solutions that are made carefully with known concentrations. A solution with a known concentration is called a standard solution. There are two ways to prepare an aqueous solution with a known concentration. You can make a solution by dissolving a measured mass of pure solute in a certain volume of solution. Alternatively, you can dilute a solution of known concentration. In this lab you will practice preparing solutions of known concentration following the proper procedure and using the appropriate equipment. To test the accuracy of your measurements you will attempt to layer your solutions according to their density.

Purpose (2 marks, C)

______

Materials

SCH3U Lab 4.2 Name:______

Goggles and apron

Large test tube (110 mL)

25 mL Graduated cylinder

Granulated Sucrose

Sucrose stock solution – 5.84 mol/L

Distilled water

Food colouring

10 mL Pipette

Glass stir rod

5 small beakers

Retort stand and test tube clamp

SCH3U Lab 4.2 Name:______

Pre Lab (16 marks, I)

Calculate the missing data for solutions 1 to 4 and write it in Table 1 and 2. Show all calculations below and include all units.

Solution 1 / Solution 3
Solution 2 / Solution 4

Table 1: Preparing Solutions from a Stock Sucrose Solution (2 marks, C)

Solution # / Food Colouring / Conc of Stock Solution (mol/L) / Volume of Stock Solution Used (mL) / Total Volume of Solution (L) / Final Conc of Solution (mol/L)
1 / 1 drop blue / 5.84 / 0.025 / 5.11
2 / 1 drop green / 5.84 / 15.6 / 0.025

Table 2: Preparing Solutions from Solid Sucrose (6 marks, C)

Solution # / Food Colouring / Mass of Granulated Sucrose (g) / Molar Mass of Sucrose (g/mol) / Number of Moles of Sucrose (mol) / Total Volume of Solution (L) / Final Conc of Solution (mol/L)
3 / 2 drops yellow / 342.30 / 0.025 / 2.19
4 / 1 drop red +
2 drops yellow / 6.25 / 342.30 / 0.025
5 / 2 drops red / 0.00 / 342.30 / 0.025

Procedure:

Preparing Solutions by Diluting

__ 1.  Prepare solution 1 from the stock solution

a.  Measure the correct volume of stock solution into a 25 mL graduated cylinder.

b.  Add water to the same graduated cylinder until the meniscus is at the 25 mL mark.

c.  Transfer into a small labeled beaker.

d.  Add the food colouring and stir with a glass stirring rod.

e.  Carefully and slowly transfer your solution to the test tube by pouring it down the side of the test tube – the slower you add the solutions to the test tube the less the layers will mix together.

__ 2.  Repeat for solution 2.

Preparing Solutions from a Solid

__ 3.  Prepare solution 3 from the solid sucrose:

a.  Obtain the required mass of sugar and transfer into a 25 mL graduated cylinder.

b.  Add water to the same graduated cylinder until the meniscus is at the 25 mL mark.

c.  Transfer into a small labeled beaker.

d.  Add the food colouring and stir with a glass stirring rod.

e.  Use the pipette to SLOWLY add this layer. – the slower you add the solutions to the test tube the less the layers will mix together. Keep the pipette low into the test tube.

__ 4.  Repeat for solution 4 and 5.

__ 5.  Present your final product to the instructor to be graded.

(1 mark/layer = 5 marks, I)

__ 6.  Divide the clean up fairly between yourself and your partner. Make sure all glassware that came into contact with a sucrose solution is thoroughly washed. Put away all of the equipment and then return to your lab area and wipe the lab bench with a wet towel.

Analysis Questions:

1.  Why were the different sucrose solutions able to remain separate from one another? (1 mark, A)

2.  Without physically mixing the layers how could you speed up the process of the layers merging together? (1 mark, A)

3.  Explain two things you could do to improve this experiment. (2 marks, A)

4.  For solution 1 answer the following and show any calculations.

a) What mass of sucrose is in the final solution? (4 marks, I)

b) How would you find the mass of sucrose in the initial solution? (1 mark, I)

5.  For solution 2, what mass of sucrose is in the initial solution? Show your calculations. (4 marks, I)

b) How would you find the mass of sucrose in the final solution? (1 mark, I)