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Acidity of Beverages Lab

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Raymond Surya

on 6 January 2015

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Transcript of Acidity of Beverages Lab

AP Chemistry
Acidity of Beverages Lab
Izak Fritz
Evan Overweg
Raymond Surya

How can we determine the acid content in various beverages?
1. Label the three test tubes B, P and T for each indicator.
2. Use the graduated cylinder to measure and pour 2.0 mL of acetic acid into each test tube.
3. Add 2 drops of indicator to the appropriate test tube.
4. Observe and record the initial color of indicator in each test tube.
5. Measure 9 mL of NaOH into a beaker.
6. Use a graduated pipet to 3 mL of NaOH to each test tube in 1 mL increments, recording the color and volume of NaOH added every increment.
7. Choose a suitable indicator for determining endpoint of neutralization for a weak acid and strong base.
Procedure (Day 2)
1. Measure 20 ml of beverage sample with a graduated cylinder, then put it into an Erlenmeyer flask.
2. Set up a support stand and attach a buret clamp. Place the magnetic stirrer on the base of the support stand, and but the buret on the clamp.
3. Put the beverage on the magnetic stirrer, and put the stir bar in the flask and turn on the stirrer. Add 2 drops of the indicator chosen in day 1.
4. Make sure the buret's stopcock is closed and measure 24-25 mL of NaOH into the buret.
5. With the magnetic stirrer on, begin adding the sodium hydroxide to the beverage until the color associated with the endpoint of neutralization found in part 1 is reached. Record the amount of NaOH remaining in the buret.
6. Repeat steps 1-5 two more times to more accurately determine the acid concentration in the beverage.
7. Repeat Steps 1-6 for another beverage if desired.
Results (Day 1)
.1M Acetic Acid
.1M Sodium Hydroxide, NaOH
Beverage Samples, milk and apple juice
Distilled water
Beaker, 50 mL
Graduated Cylinder, 10 mL
25 mL buret
Medium test tubes, 3
Support stand and buret clamp
Test tube rack
Indicator, bromthymol blue, phenolphthalein, thymol blue
Beral-type graduated pipets
Volumetric flask
From the data, we know that phenolphthalein had the most obvious color change when the pH was neutral, which was when 2.0 mL of the Acetic acid was mixed with 2.0 mL of the NaOH, so it would be the best choice for Day 2.
Results (Day 2)
This is the amount of 0.1M NaOH needed to neutralize 10 mL of Apple Juice or Milk. The main source of acid in Apple Juice is malic acid, which neutralizes two molecules of OH− for every molecule of malic acid.
Results (Day 2) Continued
The top equation represents the malic acid content in apple juice, which is a diprotic acid, meaning that it takes 2 moles of OH- to neutralize 1 mol of malic acid.

The bottom equation represents the lactic acid content in milk, which is a monoprotic acid, meaning that it takes 1 mol of OH- to neutralize 1 mol of lactic acid.
The concentration of acid in a beverage can be determined by titrating the beverage with NaOH. Malic acid and lactic acid are the acids present in apple juice and milk, respectively. In malic acid and lactic acid, there are carboxylic acid groups (COOH), with malic acid having 2 and lactic acid having 1. This is where the acidic hydrogen comes from when it reacts with NaOH. Despite some sources of error, this experiment was a success, and shows how titration can be used to measure the acidity of beverages.
Sources of Error
1. Apple Juice sometimes has citric acid added when it is processed, so this is a possible source of error, as some of the NaOH would have been used to titrate a different acid, leading us to predict a higher concentration of malic acid in apple juice.
2. Too much NaOH may have been used to titrate the beverages because the titration point was not clear; as we added more base, the beverages continued to grow more pink.
3. The milk had been sitting out before being tested and may have grown more sour, leading us to predict a higher concentration of lactic acid in milk.
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