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Copy of How Much Acid is in Fruit Juice & Soft Drinks?

By Melissa Kulaprathazhe, Shaina George & Angie Lin

Melissa Kulaprathazhe

on 8 June 2015

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Transcript of Copy of How Much Acid is in Fruit Juice & Soft Drinks?

Lab #4: How Much Acid is in Fruit Juice & Soda?
Hypothesis: We believe that the white grape juice will have the lowest pH, or the most citric acid (H+concentration). Grapes themselves are quite acidic, caused by the presence of tartaric acid and malic acid, therefore the juice itself should also be quite acidic.







1. Watch the complete chemical equation for the reaction of a solution of sodium hydroxide (NaOH) with hydrochloric acid (HCl).
NaOH +HCl >>>>>>>>>> NaCl (aq)+HOH
2. How many mL of 0.1 M HCl are required to react completely with 5mL of 0.1 M NaOH?
X= 5 mL
3. If equal molar amounts of NaOH and HCl are mixed, when the reaction is complete what will be the chemical species in the resulting solution?
In the resulting solution, the chemical species will consist of an aqueous solution of water, Na+ ions and Cl- ions.
4. Will the pH of the mixture in question 3 be acidic, neutral or basic? Explain.
The pH of the mixture will be basic because you are mixing a strong base and a strong acid so therefore the solution will be basic with a possible pH of 7.
5. Write the complete chemical equation for the reaction of a 0.1 M solution of acetic acid (CH3COOH) with a 0.1 M solution of NaOH?
CH3COOH +NaOH >>>>>>>>>>>>>Na+ + HOH+ CH3COO-
6. How many mL of the 0.1 M NaOH solution will required to react completely with 5mL of 0.1 M of acetic acid solution? Explain.
5ml of the NaOH will be needed to titrate the acetic acid solution. Even though NaOH is a strong base the same amount of acid will be needed to titrate. Using the formula MaVa=MbVb, you can find the volume needed for the experiment.
7. When the reaction is complete what will be the pH(acidic, neutral, basic) of the solution in question 6? Explain.
The reaction is actually quite basic because you are mixing a strong base and a weak acid. Because it a weak acid ionizes less, therefore, making the solution basic.
8. How is it possible to determine when an acid-base reaction is complete when the concentration of one of the reactants is unknown?
When using an indicator, a slight color change should be noted when an acid-base reaction is complete. Using this information and the equation MAVA=MbVb, you can find the concentration of the missing value.
9. Using the table below, explain how indicators are chosen and used during titrations.
Indicator pH range Color Change
Methyl orange 3.1–4.4 Orange to yellow
Methyl red 4.2–6.2 Red to yellow
Bromthymol blue 6.0–7.6 Yellow to green-blue
Phenolphthalein 8.3–10.0 Colorless to pink
Thymol blue 1.2–2.8 Red to yellow
Using the Ka value of the acid prominent in these solutions, you can relate the pH range of the indicator with the Ka value. At equivalence point pH=pKa(-log[Ka]). Using this method, the Ka value for citric acid is 3.2*10^-7 and so the negative log value of that is located in the phenolphthalein range.
Pre-Lab Questions:
Citric Acid, which is the most abundant acid in all of the carbonated beverages and fruit drinks chosen, has a great effect on the pH of soft drinks and fruit juices. Although other acids, such as malic acid are present in sparkling flavored water and the other beverages, it is quite weak and therefore doesn’t have a significant effect on the pH as the citric acid does. Citric acid is a normal component of human cells that is metabolized, degraded, and eliminated from the body. It is one of the main ingredients in the food and beverage industry because it is easily obtained in large quantities, healthy and cheap. It is weak naturally occurring acid that is soluble in most liquids and used for its preserving qualities(increases shelf-life), and flavor component (slight tart, yet refreshingly sour). Citric acid is used for its health benefits and in food, alcohol and insecticide production. It is the most frequently used preservative in the world today. There are three types of Citric acid, however, the one used in the soft drinks and juices contains the formula C6H8O7. Some health benefits of citric acid include reduced nausea, prevention of kidney stones, mineral absorption, and lightening of the skin.

Tartaric acid(C4H6O6) is believed to be the acid commonly found in grapes, and grape juices/wines. It is highly acidic compared to citric and malic acid, therefore can be the cause of low pH. Tartaric acid is commonly found solely in grapes and is rarely found in other fruits. The biologically stable acid, resistant to microbial attacks and is therefore chosen as the acid in grape juices and wines. Tartaric acid is similar to citric acid in its effects to the body, however it is highly toxic if consumed raw and in large amounts.

The amount of acid in juices can be determined by acid-base titrations with a standard solution of sodium hydroxide. Many common acids have harmful effects on the body. Excess levels of these acids can harm tooth enamel. It can reduce and erode the hardness of enamel by almost half which can increase susceptibility of tooth decay, infections and other various complications. Excess amounts of acids (commonly found in juices and drinks) in the body can cause problems with the stomach including vomiting, diarrhea, nausea, loss of appetite, increased amount of sweating and swelling and abdominal pain. It can also cause a loss of fructose absorption which can cause a drop in blood pressure, dizziness, or fainting.
Background Information
1) White Grape Juice
2) CapriSun (Colorless)
3) Sprite
4) Pomegranate Cherry Seltzer(Water)
5) Phenolphthalein (8.2-10.0)
6) pH Probe
7) 100 mL Beakers
8) 100mL Graduated Cylinders
9) 0.1 NaOH
10) Burette
11) Distilled Water
12) LabQuest
13) Clamp
14) Ring stand
15) Goggles
16) Lab Aprons
17) Gloves
- Be sure to wear chemical splash goggle while conducting this experiment.
- Fruit juices and sodas will leave a sticky residue on the lab desks and glassware, so all surface should be washed prior to leaving the lab.
- Because some indicators are flammable be sure to keep away from flames and sparks.
- Wash your hands thoroughly after each experiment
-Make sure to wear an apron to prevent skin damage from chemical spills, however this experiment will not require such precautions.
Safety Procedures
1. Gather all materials necessary for the experiment.
2. Prepare a 0.1 M of 100 ml NaOH solution from the given concentration using the graduated cylinder. By using the equation, M1V1=M2V2. Data and Calculations are in the Data Section. Please refer for math-based work.
3. Fill the buret with 0.1 M NaOH solution, after rinsing the buret with NaOH. Pour 20 ml of of the flavored juice in the beaker and record the pH. (Note the initial volume of the buret).
4. Add 3 drops of phenolphthalein indicator and swirl the solution. Slowly titrate the base drop wise and consistently swirl while titrating until a color change is noted and the end point is reached.
5. Find the pH of the solution using the pH probe and record on data table, (Note volume of NaOH in buret).
6. Record the volume of the NaOH and proceed to calculate the molarity and pH of the acid(citric and tartaric).
7. Wash, and rinse the beaker after each solution. Complete steps (3-6) for each solution and for each trial. Attempt to conserve all materials and practice green chemistry.
Data Table
Suppose a student chose to measure the volumes using the beakers or graduated cylinders provided. What effect would this have had on the calculated acid concentration? How might this affect the number of significant figures in your final answers?
->Using the graduated cylinder could affect the calculated acid concentration because the measurement aren’t accurate and there can be discrepancies that could make the concentration higher or lower. This effect significant figures because you could be off by .1 M
A student rinsed the buret with water, but neglected to rinse the burette with titrant before conducting the experiment. What effect would this have on the calculated acid concentration in juice or sodas?
->If the buret is not completely dry by the time you use it, the remaining traces of water on the inside will make your titrant more dilute and thereby change its concentration.
Imagine a lab team that consistently added base past the first appearance of a pale pink color. What would happen to the average calculated acid concentration of the juices or sodas?
->The average calculated acid concentration would be lower because the the H+ will combine with OH to become H2O.
Create a diagram that shows the molecular interaction between the acid and base as the titration proceeds. Display this at four points along a titration curve: a) when 0 mL of base is added, b) when 5 mL of base is added, c) at the equivalence point, d) when an excess of base has been added., and provide an explanation for what is happening at the molecular level.

Review your graph of pH versus volume of base added. Where did the indicator change color for each trial? What was the pH associated with color change? What assumptions can you make regarding the pH at this point and the shape of your titration curve?
-> The indicator changed color at end point of the titration. The pH associated with color change is 7. After the end point any added base will increase the pH.
After conducting this experiment, what recommendation(s)might you make for a person with acid reflux disease or tooth decay despite the fact that they drink juices and diet soda? Justify your answer.
->Recommendations I would make to someone with acid reflux disease or tooth decay would be to cut down on sodas and juices. If they drink diet soda they should drink regular soda instead because diet soda wears down your tooth enamel. For juice drinks, I would drink juices with less acid. Some examples include unsweetened apple(3.4 to 4) juice, pear(3.5 to 4.6) juice, and peach(3.3 to 4) juice.
Post-Lab Questions
1. Using the titration equation (MaVa=MbVb), we will find the concentration of the juice/drink.

2. Using the equilibrium constant, we will find the concentration of hydronium ions.

3. Taking the -log of that concentration we can find the pH of the acid (juice).

4. Then we will use percent error to compare the mathematically calculated pH and the experimentally calculated pH.
Margins of Error

Passing equivalence point and adding an excessive amount of base(as seen by the color of solution)(causing an inaccurate amoun of H+ ions)
Forgetting to wipe the pH probe after inserting in various solutions and juices.
Underestimating the amount of base needed, therefore needing to prepare a new base solution.
Miscalculating the molarity and Inaccurately reading the burette
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