Inquiry: Concentration and pH of Lactic Acid

Materials:

  • Lactic Acid (Ring Pop)
  • Base: 0.10M NaOH
  • Indicator: Phenolphtalein (ptph)
  • Electronic Scale
  • Stir Stick
  • Mortar and Pestle
  • Pipette
  • Burette 10mL
  • Graduated Cylinder
  • 3 100mL Beakers
  • 250mL Beaker

Procedure:

1. Crush up ring pop into smaller pieces/crystals so it will dissolve faster
2. Measure out exactly 10g of the substance
3. Add 10g of substance to 50.0ml of water and mix until completely dissolved
4. Add exactly 10ml of your solution to 3 beakers, then add 3 drops of your indicator (phenolphthalein).
5. Fill up burette to the 50ml line with 0.10M NaOH.
6. Place beaker as well as a piece of paper underneath the burette and titrate until you see a colour change. Record the amount of NaOH used.
7. Repeat Step 6 two more times and average the three titrations.

Results and Calculations

[0.1M] NaOH used
Trial 1 7.5ml
Trial 2 7.4ml
Trial 3 7.2ml
Average 7.37ml
 

 

Analysis

The actual pH of Lactic Acid is 2.4, so our result of 2.5 is pretty decent, with a percent difference of about 4%. We can most likely attribute this inaccuracy to human error, as it is very easy to add a little most of the base (NaOH) than you actually need.

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