I.
Title: Relative Concentration of HCl (aq) and NaOH(aq)
II.
Introduction:
A. RQ. Which solution, the Hydrochloric acid or the sodium hydroxide
solution, is more concentrated?
How many times more concentrated is that solution?
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
III.
Method:
1. Choose a pigment that is one color in an acidic solution and a distinctly
different color in a basic solution. Preferably the pigment itself has neither
the acidic color or basic color, indicating it is neutral. The pigment from the
flower Echinacea was used in this experiment. It has a blue color.
It has a red color in an acidic solution. It has a green color in a basic solution.
Trial 1
2.
3.
4.
5.
Add two drops of pigment to a test tube.
Add 10 drops of HCl (aq) to the test tube. Note the color of the mixture.
Add 10 drops of NaOH (aq) to the test. Note the color of the mixture.
If the mixture is red, add additional drops of NaOH(aq) until the mixture turns
green. If the mixture is green, add additional drops of HCl(aq) until the
mixture turns red.
6. Pour the mixture down the sink, then thoroughly rinse out the test tube.
Trial 2
7. Add two drops of the pigment to the test tube.
8. Add 10 drops of NaOH(aq) to the test tube. Note the color of the mixture.
9. Add 10 drops of HCl(aq) to the test tube. Note the color of the mixture.
10. If the mixture is red, add additional drops of NaOH(aq) until the mixture turns
green. If the mixture is green, add additional drops of HCl(aq) until the
mixture turns red.
11. Pour the mixture down the sink, then thoroughly rinse out the test tube.
Trial 3
12. Add three drops of pigment to a test tube.
13. Add 15 drops of HCl (aq) to the test tube. Note the color of the mixture.
14. Add 15 drops of NaOH (aq) to the test. Note the color of the mixture.
15. If the mixture is red, add additional drops of NaOH(aq) until the mixture turns
green. If the mixture is green, add additional drops of HCl(aq) until the
mixture turns red.
16. Pour the mixture down the sink, then thoroughly rinse out the test tube.
Trial 4
17. Add three drops of the pigment to the test tube.
18. Add 15 drops of NaOH(aq) to the test tube. Note the color of the mixture.
19. Add 15 drops of HCl(aq) to the test tube. Note the color of the mixture.
20. If the mixture is red, add additional drops of NaOH(aq) until the mixture turns
green. If the mixture is green, add additional drops of HCl(aq) until the
mixture turns red.
21. Pour the mixture down the sink, then thoroughly rinse out the test tube.
22. Add four drops of pigment to a test tube.
23. Add 20 drops of HCl (aq) to the test tube. Note the color of the mixture.
24. Add 20 drops of NaOH (aq) to the test. Note the color of the mixture.
25. If the mixture is red, add additional drops of NaOH(aq) until the mixture turns
green. If the mixture is green, add additional drops of HCl(aq) until the
mixture turns red.
26. Pour the mixture down the sink, then thoroughly rinse out the test tube.
Trial 5
27. Add four drops of the pigment to the test tube.
28. Add 20 drops of NaOH(aq) to the test tube. Note the color of the mixture.
29. Add 20 drops of HCl(aq) to the test tube. Note the color of the mixture.
30. If the mixture is red, add additional drops of NaOH(aq) until the mixture turns
green. If the mixture is green, add additional drops of HCl(aq) until the
mixture turns red.
31. Pour the mixture down the sink, then thoroughly rinse out the test tube.
Trial 6
IV.
Results
The following table can be used to determine which solution is more concentrated and how
many times more concentrated that solution is compared to the less concentrated solution.
Drops of Pigment
Drops of HCl(aq)
Drops of
Final Color of
used
NaOH(aq)
Pigment
used
2
10
10
Green
2
14
10
Red
2
10
10
Green
2
13
10
Red
3
15
15
Green
3
21
15
Red
3
15
15
Green
3
22
15
Red
4
20
20
Green
4
28
20
Red
4
20
20
Green
4
27
20
Red
V.
Conclusions:
1. According to the results the NaOH(aq) is more concentrated than the HCl(aq).
When equal number drops of NaOH(aq) and HCl(aq) are added to a test tube
containing the pigment, the pigment is green. Echinacea pigment is green in
basic solutions such as NaOH(aq). For example when 10 drops of acid were
added to the pigment it turned red. When 10 drops of NaOH(aq) were added
to the test tube containing the pigment and HCl(aq) the mixture turned green.
When 10 drops of NaOH(aq) were added to the pigment it turned green.
When 10 drops of HCl(aq) were added to the test tube containing the pigment
and the NaOH(aq) the mixture remained the characteristic basic green.
2. The following table illustrates how many times more concentrated the
NaOH(aq) is then the HCl(aq):
Drops of Acid
HCl(aq)
14
13
21
22
28
26
Drops of Base
NaOH(aq)
10
10
15
15
20
20
Average
Ratio of drops of
Acid to Drops of
Base. This ratio
Approximates how
many times more
concentrated the
NaOH(aq) is then
the HCl(aq)
1.4
1.3
1.4
1.5
1.4
1.3
1.4
Therefore the base is approximately 1.4 times more concentrated than the HCl(aq). Since the acid
was added until there was more acid than base the relative concentration of the base is less than the 1.4.
For example, when 14 drops of HCl(aq) are needed to neutralize 10 drops of NaOH(aq), the base is at
least 1.3 times more concentrated than the HCl(aq) but less than 1.4 times more concentrated.
Potential errors in this experiment include the volume of the drops could be different since different
pipettes were used for the acidic and basic solutions. Also the indicator may have been slightly acidic or
basic effecting the number of drops of the less concentrated acid needed to neutralize the base.