The Museum of HP Calculators

# Henderson-Hasselbach HP-41

This program is Copyright © 2002 by David Erdman and is used here by permission.

This program is supplied without representation or warranty of any kind. David Erdman and The Museum of HP Calculators therefore assume no responsibility and shall have no liability, consequential or otherwise, of any kind arising from the use of this program material or any part thereof.

## Overview:

This program is a simple program that I normally use in my line of work.

pH=pKa+log([conjugated acid]/[acid])

The Henderson-Hasselbach equation is a mathematical statement which defines the pH of a solution of a conjugate acid-base pair in terms of the dissociation constant of the weak acid and the equilibrium concentrations of the acid and its conjugate base. When pK=pH, then, [Ha} is equal to [A]. Values of pK yield quantitative information concerning acid strength, very strong acids being characterized by undefined pK values (pK=-log 0, example HCl); semi-strong acids being characterized by small pK values; and weak acids being characterized with large pK values.

## Program

```01 LBL 'HH'
02 'PH-b OR PKA-d?'
03 PROMPT
04 LBL 'B'
05 'PKA=?'
06 PROMPT
07 STO 02
08 'CA CNC?'
09 PROMPT
10 STO 01
11 'HA CNC?'
12 PROMPT
13 STO/ 01
14 RCL 01
15 LOG
16 STO+ 02
17 RCL 02
18 'PH='
19 ARCL X
20 AVIEW
21 RTN
22 LBL 'D'
23 'PH=?'
24 PROMPT
25 STO 02
26 'CA CNC?'
27 PROMPT
28 STO 01
29 'A CNC?'
30 PROMPT
31 STO/ 01
32 RCL 01
33 LOG
34 STO- 02
35 RCL 02
36 'PKa='
37 ARCL X
38 AVIEW
39 END
```
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