Physical Science Name________________________

Lab 3.2 pH-balanced Partner___________

The pH of Natural Substances

After completing the lab, determine what its purpose was, and write it below.

Purpose:__________________________________________________________ __________________________________________________________________

Procedure:

Part 1

1. Pour 0.10 M HCl into a buret. Set at 0.00 mL.

2. Pour 20.0 mL of potash extract (from ashes + water) into a small graduated cylinder. Ideally we should be using a pipette, but we don't have 20.0 mL ones.

3. Transfer to an erlenmeyer flask.

4. Add two drops of bromothymol blue indicator. Swirl in order to mix the indicator and base.

5. Allow about 8 ml of acid to flow from the biuret into the flask containing base and indicator.

6. Slowly continue adding acid drop by drop until you see a green colour. It should not be a blue-green; keep going, but stop before seeing a yellow-green colour. Record your data below:

Data:

Volume, V₁, of HCl required (mL)

Analysis:

1. Use C₁V₁ = C₂V₂ to obtain the concentration, C_2, of the potash extract. C₁ is the concentration of acid (see procedure). V₁ = volume of acid used (see data), and V₂ is the volume of base used (see procedure).

2. C₂ obtained = [OH^-1]. To get [H⁺1], divide 10^-14 by C₂.

3. Use [H⁺1] to obtain the pH of the potash extract.

Conclusion:

Procedure:

Part 2

1. In three different test tubes, add the water obtained from melted LaurenHill- parking- lot- snow. Add enough to obtain a height of 2 cm.

2. Carefully add 2 drops of phenol red to the first test tube. Phenol red can be absorbed through the skin, and it's poisonous, so be careful.

3. Carefully add 2 drops of universal indicator to the 2nd test tube.

4. Carefully add 2 drops of bromothymol blue to the last test tube.

5. Record the colours obtained in the table below:

Data

Indicator	Colour Observed
Phenol red
Universal indicator
Bromothymol blue

Analysis:

Use the following information to determine the pH of the snow we melted.

Indicator	pH range	Colour
Phenol red	0 to 6.4	yellow
	6.4 to 8.2	orange
	8.2 to 14	red
Universal indicator	0 to 4	red
	4 to 6	orange
	6.5 to 8	green
	8 to 14	blue/violet
Bromothymol blue	0 to 6	yellow
	6 to 7.6	green
	7.6 to 14	blue

Conclusion: The pH of the snow was somewhere between ______and _____. Did the snow contain a significant amount of sulphates and nitrates assuming that these would only be found in what is officially known as " acidic precipitation"?_____________

DON"T FORGET TO GO BACK AND INCLUDE A PURPOSE TO THIS EXPERIMENT.