MY PBL PAGE

PURPOSE

A number of objectives are satisfied with this presentation, including a) demonstrating color changes of solutions due to changes in pH of the solutions, b) demonstrating the reversibility of indicator color changes, c) providing an introduction to acid/base chemistry, d) getting students to think about how acids and bases interact, and e) providing an introduction to standard indicators.

DRIVING QUESTION : How would you appear and disapper colors in the solutions?

INTRODUCTION

Clear-colored solution is added to six beakers. The second clear solution is also added to the six beakers and each beaker will turn a different color from Red, Orange, Yellow, Green, Blue, and Violet.

SCIENTIFIC PRINCIPLE

The ph indicator solution is added to find out the level of acidity of the solutions in the pipets. There are 6 different solutions in the pipets and when it mixes with both the hydrohloric acid and sodium hydroxide it determines the color of that solution.

MATERIALS

Hydrochloric acid solution

Sodium hydroxide solution

Six pipettes of whole/combination indicator solutions:

Phenolphthalein

Thymolphthalein

P-nitrophenol

PROCEDURES

  1. Pour 3 drops of each of six pH indicators into the six beakers.

  2. Pour 50 mL of hydrochloric acid solution to all six beakers. The solution is clear and will stay clear until an indicator is added.

  3. Pour 75 mL of sodium hydroxide solution into the six beakers. After adding the sodium hyrdoxide solution the solutions will change to a color.

  4. Pour 100 mL of hydrochloric acid solution to the beakers and the solution color will "disappear" or turn back to clear.

SAFETY REGULATIONS

Hydrochloric acid and Sodium Hydroxide can burn skin. P-nitrophenol is poisonous if ingested, it can stain things into a yellow color. The indicator solutions contain ethyl alcohol. Be sure to wear protective clothing such as: chemical-resistant apron, chemical-splash goggles, and chemical-resistant gloves.

OBSERVATIONS AND DATA

Beaker # Indicators Color

Beaker 1 - thymolphthalein and phenolphthalein to make violet

Beaker 2 - thymolphthalein to make blue

Beaker 3 - thymolphthalein and p-nitrophenol to make green

Beaker 4 - p-nitrphenol to make yellow

Beaker 5 - phenolphthalein and p-nitrophenol to make orange

Beaker 6 - phenolphthalein to make red

The color of the solution before(because 3 dropps of indicator is put in before HCl) and after the HCl is clear.

The color of the solution after the NaOH is a different color of the rainbow in each beaker.

CALCULATIONS, FORMULAS

NaOH + HCl ----> NaCl (salt) + H20 (water)

(0.1 mol = NaOH)

(100 mL = 0.1 L)

(0.1 mol x 0.1L = 0.01)

100 mL of NaOH will be diluted with 900 mL of water

100 mL of HCl is diluted with 900 mL of water