Candy Acid Lab

Purpose: To randomly select an acidic substance and find it’s pH and Concentration through titration.

Materials:

1. 6.63g of solid Acetylsalicylic Acid/A.S.A (Aspirin)
2. 0.1M of Sodium Hydroxide (NaOH)
3. Phenolpthalein (indicator)
4. 200mL of water
5. 500mL beaker
6. 3 80mL beaker
7. Mortar and Pestol
8. Stir stick
9. Hot plate
10. Pipette

Procedure:

Step 1: Grind A.S.A with Mortar and Pestol until fine powder.

Step 2: Measure mass of A.S.A on scale.

Step 3: Add A.S.A to beaker filled with 200mL of water.

Step 4: Place beaker on hot plate. Heat and stir with stir stick until completely dissolved.

Step 5: Once the A.S.A has dissolved, remove from hot plate.

Step 6: Take pipette and transfer 10mL into 80mL beaker 3 times (separate beakers).

Step 7: Add 3 drops of Phenolpthalein to each beaker.

Step 8: Titrate solution by adding NaOH and stir until pink.

Step 9: Record difference between initial and final volume of NaOH for each beaker and average values.

Results and Calculations:

Titration:

Average volume of NaOH: 7.5mL

Finding Concentration and pH:

[C₉H₈O₄] =  x = 0.184M

Ka=

3.16 x 10^-4 =

X = 7.63 x 10^-3M

pH = -log(7.63 x 10^-3)

pH = 2.12

Actual pH = 2.62

Analysis:

After completing the testing, my group found good results. We first calculated the concentration of the Aspirin. The Aspirin was in pill form so in order to measure concentration, we had to grind the A.S.A using a Mortar and Pestol and then dissolve it in water to create a solution. We then calculate and found the concentration to be 0.184M or . Once we found the calculation we had the information necessary to find the pH. We used an ice chart to develop a formula to find the concentration of H₃O⁺ from our initial concentration of Aspririn and it’s Ka. We found the concentration to be 7.63 x 10^-3M and from that we found the pH of the solution to be 2.12. As you can see above, this value is slightly off from the actual pH of Aspirin. There are a number of factors contributing to this however the presumed main reason of this outcome was the Aspirin was not able to completely dissolve in the water. After attempts to dissolve the A.S.A in solution, by heating and stirring the contents in the beaker, a fraction of it was unable to do so. Because of this, the concentration of the solution would have be affected and from that, the pH would be affected as well.