Question 18
Think like a scientist: Making different concentrations of a solution
You will need: safety glasses; test tubes; test tube rack; pipette; two measuring cylinders, suitable for measuring 10 cm³; concentrated solution of food dye; beaker of water.
Method
1 Carefully measure out 10 cm³ of the concentrated food dye solution. When you have added about the correct volume you can use the pipette to add or remove the final amount drop-by-drop, so that your measurement is as accurate as possible. Place it in a test tube and leave it in the test tube rack. This is solution A.
2 Carefully measure another 8 cm³ of the concentrated food dye solution. Pour it into a test tube.
3 Measure out 2 cm³ water and add it to the 8 cm³ of food dye. Leave it in the test tube rack. This is solution B.
4 Use the table below to make up food dye solutions C, D and E. Place the solutions in the test tube rack, in order, from A–E.
| Solution | Volume of concentrated food dye solution in cm³ | Volume of water in cm³ | Total volume in cm³ |
|---|---:|---:|---:|
| A | 10 | 0 | 10 |
| B | 8 | 2 | 10 |
| C | 6 | 4 | 10 |
| D | 4 | 6 | 10 |
| E | 2 | 8 | 10 |
5 Look carefully at the solutions you have made.
Why is it important to measure the food dye solution and the water accurately?
You will need: safety glasses; test tubes; test tube rack; pipette; two measuring cylinders, suitable for measuring 10 cm³; concentrated solution of food dye; beaker of water.
Method
1 Carefully measure out 10 cm³ of the concentrated food dye solution. When you have added about the correct volume you can use the pipette to add or remove the final amount drop-by-drop, so that your measurement is as accurate as possible. Place it in a test tube and leave it in the test tube rack. This is solution A.
2 Carefully measure another 8 cm³ of the concentrated food dye solution. Pour it into a test tube.
3 Measure out 2 cm³ water and add it to the 8 cm³ of food dye. Leave it in the test tube rack. This is solution B.
4 Use the table below to make up food dye solutions C, D and E. Place the solutions in the test tube rack, in order, from A–E.
| Solution | Volume of concentrated food dye solution in cm³ | Volume of water in cm³ | Total volume in cm³ |
|---|---:|---:|---:|
| A | 10 | 0 | 10 |
| B | 8 | 2 | 10 |
| C | 6 | 4 | 10 |
| D | 4 | 6 | 10 |
| E | 2 | 8 | 10 |
5 Look carefully at the solutions you have made.
Why is it important to measure the food dye solution and the water accurately?
