Practical session 5

Question 1

What is the title of the practical?

Answer 1

Sodium Analysis by Standard Addition.

Question 2

What are the aims of the practical?

Answer 2

1. Build up atomic emission/flame emission theory.
2. Practice standard addition calibration.
3. Understand prediction error from results calculated.

Question 3

What do some metals produce, when heated?

Answer 3

A coloured flame.

Question 4

What is an example of flame creation when metals are heated?

Answer 4

Fireworks.

Question 5

How can the light emitted from the heated metals be used?

Answer 5

To find how much is present, following the Beer Lambert Law.

Question 6

Who check the supermarket products?

Answer 6

Agencies.

Question 7

What is the purpose of this practical?

Answer 7

To find if the milk from the supermarket contains what it says it contains on its label with nutritional information.

Question 8

How will the milk be determined in this test?

Answer 8

Using a flame photometer.

Question 9

What will the flame photometer cause to the samples?

Answer 9

A change of the colour in the flame of the samples.

Question 10

How will we find what the milk contains by heating up 6 standards and 4 unknowns into the flame of the flame photometer?

Answer 10

We will see a colour change in the samples caused by the heat.
We will record the colours.
We will try to identify the unknowns.

Question 11

What is the method of sodium analysis of milk?

Answer 11

1. Pipette 10mL of milk into a 100mL flask. Make up to the mark with distilled water. Label it as Solution A.
2. Pipette 50mL of Solution A into a 1000mL flask. Make up to the mark with distilled water and call it Solution B.
3. Take the 0.10 M sodium standard and dilute to produce a 0.001 M standard. Label it appropriately.
4. Take 0, 2, 4, 6, 8, 10mL of this 0.001M standard in separate 100 mL flasks.
   Calculate how much these additions will increase the sodium concentration in each flask.
5. Pipette 50mL of your diluted milk (Solution B) into each flask and make up to 100mL with distilled water.
6. If the flame photometer is not on, check everything is off. Then switch on power, turn on the gas, set the fuel control to on and press the ignition switch. Select the calcium filter and leave to warm up.
7. Aspirate distilled water and set the meter to zero using the “blank” control (zero standard).
8. Aspirate your most concentrated standard and adjust to 100% using coarse and fine sensitivity controls.
9. Check your blank reading and repeat steps 8 and 9 until your 0 and 100% readings are stable.
10. Aspirate your 6 standards ensuring you aspirate distilled water between samples to avoid contamination.
11. To produce a calibration curve and calculate the sodium concentration. Note that you will need to choose an x-axis with negative values.
12. Convert sodium concentration from mol L-1 to mg L-1 in your sample and in the original milk.
13. You will need to enter your data on the spreadsheet at the front of the class.
14. Determine the prediction error associated with your result (this will be covered in the statistics sessions).