pH vs. Concentration of Hydrogen Ions

 

Background:  The pH scale is related to the concentration, measured in Molarity, of Hydrogen or Hydronium ions in solutions.

 

Purpose: To determine the mathematical formula for the relationship between the pH and the H+ concentration --> [H+].

 

Lab Set-up:

1) Obtain a Microscale well plate that contains wells just large enough to fit a pH probe.

 

2)      Using a solution of 0.01 M HCl, a series of 5 dilutions are to be performed and the pH recorded for each.  Two additional solutions, numbers 6 and 7, have been created for you to test as well. 

 

CBL SET-UP

1)      Connect a pH probe to Channel 1. Connect the Calculator to the CBL. Turn on both the calculator and CBL.

2)      From the APPS menu on the calculator, Select CHEMBIO.  The following screens will appear.

 

 

 

 

 

 

 

3) Select  SET UP  PROBES from the main menu and select a pH probe from the list of probes.  Select USE STORED from the calibration menu when prompted.  The main menu screen should return following the set-up process

 

DATA COLLECTION.

 

1) From the main menu select COLLECT DATA.  The following screen will appear.

 

Select TRIGGER/PROMPT

 

 

 

 

 

2) Press enter when you are ready to collect data.

3) Place the pH probe in the first solution.  When the reading on the CBL stabilizes, press TRIGGER on the CBL.  The following screen will appear.

Input the [H+] from the table below in the ENTER VALUE location on the calculator.

 

Place the pH reading in the table below.

 

 

 

 


Table of Data:

 

 

1

2

3

4

5

6

7

Drops of HCl

50

40

20

5

1

xx

xx

Drops of Water

0

10

30

45

49

xx

xx

[H+] Molarity

0.01

0.008

0.004

0.001

0.0002

.00001

.0000001

pH

 

 

 

 

 

 

 

 

3)      Remove the pH probe, rinse with water and dry it off.

4)      Select MORE DATA from the menu on the calculator.

5)      Repeat steps 3-5 for each of the solutions in the table above.

6)      When all the solutions have been tested, select STOP from the menu. 

7)      Select NO from the repeat menu and the main menu should return.

 

Using either the graphing calculator or Graphical Analysis  on the computer, determine the best mathematical fit to the data.

 

Conclusion: Write the best-fit mathematical formula for the relationship between pH and the amount of Hydrogen ions in solution.