EXPLORATION 2C

EXPLORATION 2C:

WEST-GAEKE METHOD: calibration curve (60 min)

Pipet exactly 10 mL of standard sulfite solution into a 100-ml volumetric flask and dilute to the mark with absorbing reagent (0.1 M sodium tetrachloromercurate). The final solution contains 3.5 ml SO₂ per milliliter.

Add accurately 0.5, 1.0, 1.5 and 2.0-mL portions of the dilute standard sulfite solution to a series of testing tubes. Mark them as (1), (2), (3) and (4).

Add accurately the following volumes of 0.1 M sodium tetrachloromercurate to the corresponding tubes:

(1) 9.5 mL

(2) 9.0 mL

(3) 8.5 mL

(4) 8.0 mL

Add 10 mL of absorbing regent (0.1 M sodium tetrachloromercurate) to the tube marked (0). This is going to be your blank solution.

To each tube add accurately 1 mL of acid-bleached pararosaniline solution and 1 mL of formaldehyde solution and mix using a glass rod. Hold for 20 min at room temperature. (while waiting for color development you can start EXPLORATION 2D)

Look to Appendix IV in your CHEM 104.1 lab manual to see how to use the spectrophotometer

Measure the absorbance at 57O nm against the zero standard.

Plot the absorbance as the ordinate against the micrometers of SO₂ per 10 mL of absorbing solution. Compute the slope and intercept.

Calibration solutions

TESTING TUBE #

ML OF STANDARD SO₂ SOLUTION

CONCENTRATION OF SO₂[mL/10ml]

ABSORBANCE AT 570 [nm]

1

0.5

2

1.0

3

1.5

4

2.0

y= ax +b

a=

b=

	Pipet exactly 10 mL of standard sulfite solution into a 100-ml volumetric flask and dilute to the mark with absorbing reagent (0.1 M sodium tetrachloromercurate). The final solution contains 3.5 ml SO₂ per milliliter.
	Add accurately 0.5, 1.0, 1.5 and 2.0-mL portions of the dilute standard sulfite solution to a series of testing tubes. Mark them as (1), (2), (3) and (4).
	Add accurately the following volumes of 0.1 M sodium tetrachloromercurate to the corresponding tubes:

	Add 10 mL of absorbing regent (0.1 M sodium tetrachloromercurate) to the tube marked (0). This is going to be your blank solution.
	To each tube add accurately 1 mL of acid-bleached pararosaniline solution and 1 mL of formaldehyde solution and mix using a glass rod. Hold for 20 min at room temperature. (while waiting for color development you can start EXPLORATION 2D)
	Look to Appendix IV in your CHEM 104.1 lab manual to see how to use the spectrophotometer
	Measure the absorbance at 57O nm against the zero standard.
	Plot the absorbance as the ordinate against the micrometers of SO₂ per 10 mL of absorbing solution. Compute the slope and intercept.

TESTING TUBE #	ML OF STANDARD SO₂ SOLUTION	CONCENTRATION OF SO₂[mL/10ml]	ABSORBANCE AT 570 [nm]
1	0.5
2	1.0
3	1.5
4	2.0