Lab Report:
Purpose:
The Objective of this lab was to learn how to measure the pH (or acidity) of commonly known fluids, using the correct tools and procedures. To then use that data to document the changes noticed when mixing those same fluids and changing their respective pH levels.
Materials:
In order to conduct this experiment several pieces of equipment and other materials were needed. The first item was a graduated cylinder, which was used in order to measure out the precise amount of fluids needed in the experiment. A 100mL glass beaker was used to house the measured fluids for pH testing as well as for mixing (requiring a stir). An already calibrated pH meter was used to test the levels of pH in each solution. A hammer, paper towel and Rolaid tablet were also provided and used to crush up the antacid tablet. In addition to these few pieces of equipment, specifically measured amounts of the following fluids/substances were used: tap water, distilled water, soda, milk, lemon juice, and dissolved Rolaid solution (mix of an antacid tablet and 50mL of distilled water).
Method:
The subsequent steps were used to preform the pH measuring experiment: My group, comprised of six students, gathered the required equipment from our lab TA – one graduated cylinder, four beakers, hammer, paper towel, Rolaid tablet, a stir and a pH meter. Each of the four beakers and the graduated cylinder were rinsed using tap water before any liquids were poured into them. One group member filled the graduated cylinder with 50mL of tap water and then transferred the liquid into a beaker. This process was repeated for soda, distilled water and milk. The pH meter was turned on, placed in each beaker and remained until the numbers on the tools screen stopped flocculating. Each reading was then documented on the provided data sheets.
The beaker containing the tap water was emptied. Using a clean graduate cylinder 10mL of lemon juice and 40mL of water was measured out and added to a beaker. The liquids were combined and measured for their pH level. Next a Rolaid tablet was wrapped in a paper towel, crushed with a hammer and added to the beaker containing distilled water. Each new solution was measured and recorded. The mixed solutions were used for the next portion of our experiment. Using a clean graduated cylinder, 10mL of the antacid solution was added to the soda beaker, mixed and the pH level was measured. This process was repeated twice, adding an additional 10mL each time. Using the beaker containing milk, the same experiment was carried out using the lemon juice mixture. 10mL of lemon juice mixture was measured, added to the milk beaker, mixed and measured for pH levels. This process was repeated twice, once again adding an additional 10 mL of the diluted lemon juice solution each time.
Results:
Liquid
Initial pH
1. Tap Water
7.29
Weakly Basic
2. Distilled Water
5.66
Weakly Acidic
3. Soda
2.23
Strongly Acidic
4. Milk
6.73
Weakly Acidic
5. Dilute (1:5) lemon juice
2.14
Strongly Acidic
6. Dissolved Rolaid solution
7.40
Weakly Basic
The data in the above table is pretty straightforward. Each liquid was measured and recorded in the appropriate section. Tap water had to be measured twice – original recording was excessively acidic.
Antacid – Soda Solution
mL of Antacid Solution
pH
0
2.23
Strongly Acidic
10
2.93
Strongly Acidic
20
4.61
Weakly Acidic
30
5.03
Weakly Acidic
As expected, Rolaid is an Antacid (designed to naturalize acid) and it raises the pH number of an already acidic solution, making it less acidic. The first box represents just the pH level of soda, as identified in the earlier table. As each additional 10mL of antacid solution was added, the level of acidity begins to neutralize or decrease. The changes appear more drastic after the second 10mL is added.
Lemon Juice – Milk Solution
mL of Dilute
pH
0
6.73
Watery
Weakly Acidic
10
5.38
Starting to separate
Weakly Acidic
20
4.70
Lumpy
Strongly Acidic
30
3.77
Curdled
Strongly Acidic
Starting from the first pH measurement in the above chart (just milk), the liquid is clearly weakly acidic. As the acidic level was increased through 10mL incremental additions of the lemon juice solution, the acidity level raises and pH lowers. The appearance of the milk begins to separate and create chunks. The acidity of the lemon juice causes the milk to curdle or “go bad”.
Discussion and Conclusions:
pH, or the potential for hydrogen, is naturally occurring in life forms as well as most echo systems. A delicate balance is usually struck, finding a healthy and sustainable range of pH. Changes to this have proved to cause drastically negative side effects.
Using the equipment provided, this lab allows one to simulate and force changes in pH levels. The clean beakers provided an environment in which all other factors could be removed. The pH meters gave slightly different
readings in the same solution but all readings were relatively close.
The milk – lemon juice experiment demonstrates the effect that a highly acidic additive will have on a solution that possesses weakly acidic qualities. The entire composition of the milk visually changes before us in only a matter of seconds. On the other hand, the mixing of the antacid shows an example of a buffer and its characteristics. Although this particular buffer is artificially created, buffers do occur in nature, as well. Buffers provide a means to combat acidity.
Simply put, changing the pH of any liquid can give way to a fundamental change in the properties of liquids. It is then safe to assume that these same changes can occur in nature and cause damage to life forms and echo systems.
Questions:
1. Describe the relationship between pH of soda and the quantity of antacid. Is the relationship increasing or decreasing? Is the relationship linear or does it appear that the pH is approaching a plateau?
Soda is classified as a strongly acidic liquid. The pH of just soda alone is 2.23. After adding the antacid solution, an artificially created buffer, the pH of the soda begins to increase. This in turn means that the acidity of the soda is being naturalized or reduced by the properties of the antacid. The relationship between the two, as well as the pH figures of the combined solution appears to be reaching a plateau.
2. Describe the relationship between pH of milk and quantity of dilute lemon juice. Is the relationship increasing or deceasing? Is the relationship linear or does it appear that the pH is approaching a plateau?
Milk has a pH of around 6.73, which classifies this fluid as weakly acidic. As the lemon juice solution, a strongly acidic liquid, is added to milk, the liquid become increasingly more acidic. The milk begins to take on the pH
properties of the lemon juice. The relationship between the two appears to be linier.
3. How does the soda- antacid relationship compare to the milk-lemon juice relationship?
The soda-antacid and milk-lemon juice relationships are both examples of solutions with opposing pH levels being combined and changed. The difference that becomes apparent is that the soda-antacid solution demonstrates a buffers property, which simply attempts to naturalize, not completely change the pH properties of another liquid. The experiment between milk and lemon juice completely changes the properties of the milk and the lemon juice dominates the pH levels.
4. What happens to milk as more lemon juice is added? Explain your observation on the basis of the observed pH changes.
As lemon juice is added to milk the changes can be seen, even without testing the solution. Each time an additional 10mL of lemon juice is added the milk a separation process begins to occur. The original liquid is mercy but smooth. After the first 10mL not much visible change happens. With the second 10mL the milk begins to grow thicker and lumpy. Once the last addition of 10mL is added, the milk completely curdles and turns to chuncks.
5. If some stomach upsets are caused by an excess of acid, why does chewing antacid tablets help to reduce the discomfort?
Excess amounts of acid in a person’s stomach causes an increase of pH levels in the human body. This experiment has demonstrated that even small changes can make major differences. Chewing an antacid pill can naturalize pH levels and bring them back to their naturally occurring and healthy state. This should hopefully reverse or minimize any symptoms, such as pain.
6. What is the normal pH of blood in the human body, urine, saliva, and beer?
The pH level in human blood ranges from 7.35 – 7.45. The range in urine fluxuates between 4.6 and 8 (7.4 being the average). Saliva has a normal pH of between 5.6 and 7.9. Beer has a lower pH of between 3.7 and 4.5
7. At what pH do fish in lake ecosystems fail to reproduce?
At pH levels below 6 fish can no longer reproduce. At levels below that the fish can begin to die.
8. How does a buffer work?
A buffer is a substance that that acts as a neutralizes acids or bases. The chemical properties in buffers naturally absorb the change in pH, stabilizing the pH levels.
9. What are at least two examples of natural buffers?
Two examples of natural buffers are amino acids and phosphate. Several natural buffers are found within the human systems that help with digestion and other functions.
10. During an autopsy, the Medical Examiner found that the deceased had dies from a condition known as alkalosis. Alkalosis is a condition that occurs when the pH of the blood rises significantly above 7.45. Knowing that liquids in the stomach can pass into the bloodstream very quickly and knowing that the normal pH in a human stomach can pass into the bloodstream very quickly and knowing the normal pH in a human stomach is between 1.5 and 3.5, the Medical Examiner examined the stomach and found the hydrogen ion [H+] concentration to be 10-12 moles/liter (0.0000000000010 moles/liter). What was the pH of the stomach?
0.0000000000010 log = 12
