Shawn910018的部落格

 Experiment date: 2013/10/18

1. Principle:

Phenolphthalein（酚酞）is usually used as a pH Indicators, and actually it has 4 different forms in acid or base. We want to use the simple way to make it, and to see how it works. The following is the pH- Phenolphthalein form table.

From：Wikipedia, http://en.wikipedia.org/wiki/Phenolphthalein

1. Chemicals and their Properties:

Phenolphthalein (C₂₀H₁₄O₄): CAS 77-09-8 318.323 g/mol d:1.277g /cm³ mp:262.5 ℃

Phenol(C₆H₅OH): CAS:108-95-2 94.11 g/mol d: 1.07 g/cm³ mp:40.5 °C bp: 181.7 °C

Phthalic anhydride(C₈H₄O₃): CAS 85-44-9 148.1 g/mol d: 1.53 g/cm³

mp:262.5 ℃ bp:295 °C

H₂SO₄: CAS 7664-93-9 148.1 g/mol d:1.84g/cm³ mp: 10 °C bp: 337 °C

NaOH: CAS 1310-73-2 39.9971g/mol d: 2.13 g/cm³ mp: 318 °C bp: 1388 °C

C₂H₅OH: 46.06844 g/mol d: 0.789 g/cm³ mp: −114.3 °C bp: 78.4 °C

1. Tools and Chemicals:

1. Phenol（苯酚）  0.1 g
2. Phthalic anhydride（鄰苯二甲酸酐）  0.1 g
3. H₂SO₄（Conc. sulfuric acid）  0.1~0.2 mL
4. NaOH（Sodium hydroxide）  2-5 g
5. 95%C₂H₅OH
6. An electronic balance
7. A heater（with a bowl of sand） 
8. A dryer
9. A box of pH indicator strip
10. Two PE Pasteur pipettes
11. A medicine spoon
12. A glass stick  
13.A sample tube shelf
14. A sample tube
15. Some pure water
16. A pair of gloves  

1. Safety and Waste Disposal:

Safety : Always wear your coat, gloves and eye protection.

Disposal: Everything with Phenolphthalein inside need to recycle in a plastic box.

1. Procedure:

Part. A

1. First, use the dryer to heat phenol(苯酚，MP:40.5℃), turn it into liquid.

2.Waight out 0.1g phthalic anhydride (鄰苯二甲酸酐) and put it into a sample tube.

3. Use a PE Pasteur pipette to take some Phenol and add two to three drops into the text tube.

4. Put in one to two drops of H₂SO₄ inside the text tube. You can find that the solid inside changed into orange.

5. Put the tube into the bowl of sand on the heater and control the temperature at 160℃ for five minets.

6. take out the tube and see the color of it and whether it is solid or liquid. If it is liquid, put it back on the heater for another 5 minets.

Part. B

1. After part. A, add 2 mL pure water into the text tube, shack the tube and it will look

white. To make us easier to see the change of the color, we will add about a mL 95% C₂H₅OH to make it looks transparent.

1. Then the second part is to Observation. First, see what color Phenolphthalein is when it

is in acid. Add H₂SO₄ slowly until it become orange. Then, use a glass stick to put some of it on the pH indicator strip and find what pH is it now.

1. Second，add NaOH at the same tube and stir it. When it become transparent, use the same way to find the pH. Keep adding NaOH and record the pH when it become red then become transparent.
2. Take photos and show the color of each form of Phenolphthalein.

1. Results:
   1. Appearance

l  From left to right pH: >14/ =14 / = 0 /0<

B. From Censer

(1)

(2)

1. Discussion:

This time our first test tube keeps looking white mix with purple, and not transport at all. But after adding alcohol, this problem is solved and we found that its pH is already over 14. Thought it could be dangerous but this make our experiment looks great. We think it is because Phenolphthalein is still not dissolve.

1. References:

The Platform of High-scope Program (http://case.ntu.edu.tw/hs/wordpress/?p=31680)

Wikipedia

1. Reflection and Feedback:

First, if we want our first (pH>14) and forth test tube (pH<0) looks beautiful, we need to be very careful because it will be very dangerous. Second, alcohol need to be added enough especially the forth tube (pH<0), or it can be not transport. Third, the pH indicator strip can’t work when the liquid’s pH is lower than 0.