Household Acids and Bases

Household Acids and Bases Lab

            Today in science we did a lab that tested the pH level of different liquids. The materials for this lab included:

computer

Vernier computer interface

Logger Pro

Vernier pH Sensor

distilled water

ring stand

sensor soaking solution

household solutions

7 small test tubes

test-tube rack

blue litmus paper

paper towel

stirring rod

red cabbage juice

250 mL beaker

and 6mL of the following:

            vinegar

            ammonia

            lemon juice

            soda

            drain cleaner

            detergent

            baking soda (mixed with about 20-25 mL OF WATER)

            milk

The pH scale is a scale used to classify different substances. Substances that are acidic have a pH level between 1 and 7. Substances that are basic (or alkaline) have a pH level greater than 7. Substances that have a pH level of exactly 7 are neither acidic nor basic. Here is a picture of the pH scale we used (Note: Alkaline means the same as basic):

            My hypothesis for this experiment was that vinegar would be an acid and have a pH of 4, ammonia would be a base and have a pH of 10, lemon juice would be an acid and have a 2 pH value, soda would be an acid and be a 5 on the pH scale, detergent would be a base and an 11 on the pH scale, baking soda would have an 10 pH and be a base, drain cleaner would be a base and have a 9 pH level, and milk would be a base and have a pH level of 8.

            The procedure for this lab was pretty simple. We tested each liquid in three different ways. First, we added a drop of each solution to blue litmus paper. We used the pH color scale to match the color of the litmus paper to the pH value of the liquid on the paper. Then we added red cabbage juice to each liquid and saw what color the solutions turned to determine the pH value.  Again we matched the color of the cabbage juice solution to the pH scale, and judged which pH each solution it was. Our last test of pH used a pH sensor. This sensor was stored in liquid that had a balanced pH level. This made the tests more accurate. Also, we cleaned the pH sensor with distilled water, (a neutral solution with a pH of 7 [meaning neither an acid or a base]), between tests to further ensure our results.  Here is a table of the results for each test:

The results were as follows:

Vinegar was proven an acid in all 3 tests and had a pH of 2 in all tests as well.

Ammonia was proven an base in the 1^st and 3^rd tests, but not in the second test. The red cabbage juice test proved it to be an acid and have a pH of 6.5, whereas the other tests said ammonia was about an 11 or 12.

Lemon juice was proven an acid in all three tests. It had a pH of 2 for the blue litmus paper test and the red cabbage juice test, but a 3.3 in the pH sensor test.

Soda had a pH level of about 3 for all tests. It was proven an acid.

Drain cleaner was the most confusing liquid. It had a pH level of about 8 for the blue litmus paper test, and a pH of about 13 for the pH sensor test. However, in the red cabbage juice test, the solution split into three layers. The top layer was greenish and had a pH of about 8. However, the middle and bottom layers were light and had an acidic pH level of about 5.

The detergent had a pH level of 10 for the litmus paper test and the pH sensor test, meaning it was a base. However, for the red cabbage juice test, the detergent had a neutral pH level of 7.

The baking soda solution had a basic pH level for all three tests. It had an average pH level between 8 and 9.

The milk had a pH level of 9 for the blue litmus paper test and the red cabbage juice test. However, it had an acidic pH level of 6.6 for the pH sensor test.

Here is a picture of our test labeled test tubes that we used:

Here is a picture of a blue litmus paper (Note: the liquid that was test on here was lemon juice, an acid, because it turned red):

Here are two pictures of the pH sensor being used to test different liquids:

My hypotheses for these experiments were usually supported. I was right about which category each substance fell under, (either acidic, base, or neutral), however, I wasn’t exactly right on the specific number each substance was on the pH scale. I was able to determine this because I learned about different liquids through an activity we did in science called “Alien Juice Bar.” We had to classify different liquids through an online simulator, and most of the liquids we tested online were the liquids we tested in this lab. I had known where each substance fell under because of that lab.

I think something that might have skewed our experiment was the red cabbage juice test. On the pH scale, basics are blue. However, none of the substances turned blue with the red cabbage juice test. I think there might have been a slightly different color scale we could have used that would have more accurately fit our results with that test.

Also, in between tests with the pH sensor, my group sometimes forgot to clean it with distilled water. This could severely altered our experiment because the pH sensor could have been measuring a different substance then what we wanted because it had the previous substance(es) on it.

Overall, this was a nice lab for a Tuesday and I learned how to classify different substances and how to tell whether they are acidic or basic. I am looking forward to applying this knowledge in chemistry in the future.