Kristin McKeown
Abby Side, Magda Soloman, Paige Romoser
Class Period 7
11 October 2011
The Effects of HCL and NaOH on Solutions
Introduction:
Problem/Question:
How does an acid HCl and a base NaOH effect tap water, pH 7 buffer, homogenized cow
liver, and homogenized potato?
Background Research:
All living organisms contain natural pH buffers within themselves. Buffers are substances
that prevent the pH level of an organism to rise up or down, their purpose is to maintain
homeostasis. This prevents ultimately from death and illness. Without natural buffers within our
bodies and the bodies of others, organisms would go extinct much more rapidly then the rate
they are going today because the pH level could drop or raise drastically just from eating certain
foods or drinking certain drinks. During this lab, tissues from organisms will be tested to see if
they contain their own natural pH buffers, therefore there would be no change to the slightest
change in the pH level upon addition of an acid or base. Organisms contain buffers because some
how, they need something within their bodies that keeps down their pH level if they eat or drink
something to acidic or basic. Also, tap water will be tested which should have a larger change in
pH, because it is not a living organism, which means that it should not contain natural buffers.
Lastly, a store bought pH buffer will be tested which should keep the pH level near seven,
because the whole purpose of buffers is to keep the pH level neutral, at 7.
Hypotheses:
If HCL, an acid is added to tap water than the level of the pH will decrease drastically
because water does not have any natural pH buffering abilities since it is not a living organism,
yet with an acid added to it which is anything less then seven, that would be the reason for it to
decrease rather than increase.
If HCL, an acid is added to pH 7 buffer than the level of the pH should remain the same
because the purpose of a buffer is to keep the pH relatively neutral at 7.
If HCL, an acid is added to homogenized cow liver and a homogenized potato, than the
level of the pH will decrease but not drastically because all living organisms have natural pH
buffers within them that controls their insides.
If NaOH, a base is added just like HCL to each substance that is being tested, than the
results will be opposite because bases are higher than acids on the pH scale.
Independent Variable:
Substances being tested: tap water, pH 7 buffer, homogenized cow liver, and
homogenized potato.
Dependent Variable:
The change in pH.
Experimental Design:
Control Group:
Tap water and pH 7 buffer with the acid and base added.
Experimental Group:
Homogenized cow liver and homogenized potato with the acid and base added.
Constant Variables:
Temperatures of the acids, bases and substances, same measurements of homogenized
potato, cow liver, tap water and ph 7 buffer, and the same amount of time to allow the acid and
base to sink within the tested substance.
Lab Safety Precautions:

Put on safety goggles and lab apron. Tie back long hair.

Avoid skin/eye contact with the acid and base, a mild irritant; do not ingest. If
contact occurs, flush affected area with water for 15 minutes; rise mouth with
water; call your teacher immediately.

Wear closed toed shoes at all times during the lab.

Do not wear any loose clothing or jewelry.
Materials:
Refer to textbook
Procedure:
Refer to textbook
Results:
When HCl, an acid was added to tap water, as the number of drops increased, so did the
pH of the tap water. Yet, the pH did not drop too drastically from its starting point of 6.60, with
20 drops the lowest pH reading was 6.11. The same applied when the NaOH was added to the
tap water, but the pH did not decrease it increased from 7.25 to 9.6 after 20 drops. While pH 7
buffer was mixed with HCl it also, did not decrease too much. Again, as the number of drops of
HCl increased, the pH lowered from 7.02 to 6.85 with 20 drops added to it. Also again, the
opposite for when NaOH, which started at 7.43 pH and with 20 drops later, the pH read 7.48. As
for the homogenized cow liver, this was a drastic change within the pH only when the HCl was
added. With 20 drops of HCl, the pH reading shot down to 4.21 a drastic change from its starting
pH of 6.81. As for when the cow liver received 20 drops of NaOH it raised to only 7.59 pH
reading from the original of 7.11. Lastly, the homogenized potato also dropped drastically from
its original pH reading of 6.42 and with 20 drops later of HCl, it soared down to 4.44. Unlike
when the NaOH was added to the potato, its original reading was 6.68 and went up to 7.21.
Conclusion:
The data that was recorded proved two of the many hypotheses to be incorrect. The
hypothesis that was proven wrong was, if HCL, an acid is added to homogenized cow liver and a
homogenized potato, than the level of the pH will decrease but not drastically because all living
organisms have natural pH buffers within them that controls their insides. When HCl was added
to the homogenized cow liver, the pH got down to as far as 4.21 and the homogenized potato
reached 4.44 each with 20 drops, as can seen by figure 1. The hypothesis stated that the pH of the
organisms would not decrease or increase too drastically because they have natural buffers
within them to keep their pH regular. This result surprised me because these organism tissues are
supposed to have natural pH 7 buffers that keep their pH level at 7, but with these results if the
homogenized cow liver or potato ever got hold of HCl, they would instantly die or be severely
sick. Another hypothesis that was proven incorrect was if HCL, an acid is added to tap water
then the level of the pH will decrease drastically because water does not have any natural pH
buffering abilities since it is not a living organism, yet with an acid added to it which is anything
less then seven, that would be the reason for it to decrease rather than increase. This was proven
incorrect because the pH level did not drop very drastically at all. The lowest pH reading that the
tap water received when HCL was added to it was only 6.11, a number that should have been
way lower. This result surprised me because with a reading like that, it would be mistaken that
the tap water has natural pH buffers within it for the final reading to be much higher then
expected. As for the rest of the hypothesizes were all proven to be accurately correct.
All of the numbers that were recorded during the experiment is the reading of the pH
after either HCl or NaOH was added to the substance. Just from reading the raw data table, it
does not appear that buffers were present in the homogenized cow liver, potato, or tap water.
But, there were obviously buffers in the pH 7 buffer, because that is its sole purpose, to keep the
pH level around 7. Just from the data table, it does not make sense that there was no buffer
within the homogenized cow liver or the potato, because all living things are supposed to contain
natural buffers to prevent them ultimately from death after being exposed to such chemicals, like
HCl or NaOH. It does make sense that there was no natural buffer within the tap water, because
water is not a living thing, it does not need to prevent its pH level from going out of whack.
As for the overall validity of this entire experiment, it was not valid. First off, we did not
have three trials of each substance being tested, which would have given us a better range for the
pH, rather than just one reading which most were wrong anyways. But, there were some
constants that were kept in mind throughout the whole experiment, such as the same temperature
of the acids, bases, pH 7 buffers, homogenized cow liver and potato, and the same amount of
time to allow the HCl and NaOH to settle down before taking down their pH. As for constants
that were actually kept constant were having the same measure of each of the substances that
were being tested. If I were to perform this experiment again, I would be sure to make time to
have three trials for each of the substances that are being tested within the lab. The control group
that was tested was the pH 7 buffer and the tap water.
Works Cited:
Glencoe/McGraw-Hill. BSCS Biology A Molecular Approach. Columbus, OH. 2006.
Pages 697-698. Print.
Miss. Ziegler’s yellow packet.
Raw Data:
Tests with 0.1M HCl (ACID)
Tests with 0.1M NaOH (BASE)
pH after addition of
pH after addition of
Solution
Tested
0 drops
5 drops
10 drops 20 drops
0 drops
5 drops
Tap Water
6.60
6.66
6.59
pH 7 Buffer
7.02
6.98
Homogenized 6.81
10 drops 20 drops
6.11
7.25
8.22
8.9
9.6
6.92
6.85
7.43
7.41
7.42
7.48
6.11
5.26
4.21
7.11
7
7.16
7.59
5.51
5
4.44
6.68
6.51
6.68
7.21
Cow Liver
Homogenized 6.42
Potato