Preparation of KHP standard solution
Theory
Materials
Chemicals
- ~22 g potassium hydrogen phthalate (KHP), ACS or USP grade
- ~1200 mL distilled water (DI)
Labware
- 1× metal spatula
- 1× 100 mL glass beaker
- 1× 500 mL glass beaker
- 1× glass stiring rod
- 1× medium glass liquid transfer funnel
- 1× 1000 mL glass volumetric flask w/ stopper, grade A
- 1× 1 L amber glass bottle
- 1× blank label (for glass bottle)
- 1× permanent marker (for label)
Instrumentation
- 1× analytical mass scale
- capacity ≥ 25 g
- uncertainty (
) ≤ ±0.5 mg
Procedure
- Weigh out a sample of KHP into the 00 mL glass beaker.
- Place the 100 mL glass beaker on the analytical scale.
- Zero the analytical scale to neglect the tare weight of the 100 mL beaker.
- Remove the 100 mL glass beaker from the analytical scale.
- Using the metal spatula, transfer roughly 20 grams of KHP to the 100 mL glass beaker.
- Place the 100 mL glass beaker back on the analytical scale.
- Wait for the analytical scale to settle on a fixed reading.
- Record the exact mass of KHP
.
- Quantitatively transfer the weighed out KHP from the 100 mL glass beaker to the 1000 mL volumetric flask using DI.
- Using the medium glass luid transfer funnel
- Bring the volumetric flask to volume with DI.
- Seal the volumetric flask with its stopper and mix well.
- Mixing is satisfactorily completed 3 minutes beyond complete dissolution of the KHP.
- Be sure to invert the volumetric flask several times while shaking to agitate the neck volume of the flask.
- Transfer the solution from the 1000 mL volumetric flask to the 1 L amber glass bottle.
- Remove the stopper form the volumetric flask.
- Ensure that the 1 L amber glass bottle is clean.
- If the amber glass bottle is visibly dirty, rinse it with DI.
- Transfer a small aliquot (10 mL to 20 mL) of solution from the volumetric flask to the amber glass bottle.
- Close the amber glass bottle and swirl the solution around, covering all surfaces, to rinse the container.
- Open the amber glass bottle and empty the contents into the appropriate waste container.
- Repeat the last three steps two more times.
- Carefully transfer the solution to the amber glass bottle.
- Label the bottle with the appropriate information.
- Solution name: "
KHP Standard"
- Date prepared: "MM/DD/YYYY"
- Name of preparer: "FirstInitial LastName"
Data analysis
The concentration of KHP in the standard can be found via straight forward dimensional analysis.
![{\displaystyle C_{KHP}={\frac {m_{KHP}}{{\overline {M}}_{KHP}}}\times {\frac {1}{V_{flask}}}={\cfrac {m_{KHP}}{204.22{\cfrac {g{\text{KHP}}}{mol{\text{KHP}}}}\times 500mL\times {\cfrac {1L}{1000mL}}}}={\frac {m_{KHP}}{102.11g{\text{KHP}}}}{\text{M}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/2037508bcd84418041481ff2e8cb52099d287ca4) | | (1) |
Error analysis
Using the standard differential error formula
![{\displaystyle \,\sigma _{f}^{2}=\sum _{i=1}^{n}{\left({\frac {\partial f}{\partial x_{i}}}\right)^{2}\sigma _{x_{i}}^{2}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/c8fb7e057e25c708b03154a3b5d6a4f5ca6f422a) | | (2a) |
or
![{\displaystyle \,\Delta f^{2}=\sum _{i=1}^{n}{\left({\frac {\partial f}{\partial x_{i}}}\right)^{2}\Delta x_{i}^{2}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/af459cbe31b7474e80e6404c30d7f8f981bcc17b) | | (2b) |
and the measurement/instrument uncertainties
the concentration uncertainty for KHP is given by
![{\displaystyle \,\Delta C_{KHP}=\pm {\sqrt {\left({\frac {\partial C_{KHP}}{\partial m_{KHP}}}\right)^{2}\left(\Delta m_{KHP}\right)^{2}+\left({\frac {\partial C_{KHP}}{\partial V_{flask}}}\right)^{2}\left(\Delta V_{flask}\right)^{2}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/a61f50c177122fc6935681a8a4ae48d2e0103e95) | | (3) |
where
![{\displaystyle {\frac {\partial C_{KHP}}{\partial m_{KHP}}}={\frac {1000{\frac {mL}{L}}}{{\overline {M}}_{KHP}V_{flask}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/a77f46760220323056da91a180691edc719cedff) | | (4) |
and
![{\displaystyle {\frac {\partial C_{KHP}}{\partial V_{flask}}}=-{\frac {m_{KHP}\times 1000{\frac {mL}{L}}}{{\overline {M}}_{KHP}V_{flask}^{2}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/b43b1ab5ee87a6d089dd01f0c229ea29d3eb1df6) | | (5) |
Substituting for the partial derivatives yields
![{\displaystyle \,\Delta C_{KHP}=\pm {\frac {1000{\frac {mL}{L}}}{{\overline {M}}_{KHP}V_{flask}}}{\sqrt {\Delta m_{KHP}^{2}+{\frac {m_{KHP}^{2}\Delta V_{flask}^{2}}{V_{flask}^{2}}}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/e6d6b85757331a77525cf3ac7d8b65ef1ba87e6f) | | (6a) |
The simplified form for the uncertainty using the example data is
![{\displaystyle \,\Delta C_{KHP}=\pm {\sqrt {5.89516\times 10^{-11}g^{-2}\times m_{KHP}+9.591\times 10^{-13}}}{\text{M}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/2f2c7d4e5131e100169fa8d62f384a00fbc29a59) | | (6b) |
which means the concentration is fully given by the equation
![{\displaystyle \,C_{KHP}={\frac {m_{KHP}}{{\overline {M}}_{KHP}V_{flask}}}\pm {\frac {1000{\frac {mL}{L}}}{{\overline {M}}_{KHP}V_{flask}}}{\sqrt {\Delta m_{KHP}^{2}+{\frac {m_{KHP}^{2}\Delta V_{flask}^{2}}{V_{flask}^{2}}}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/090b3efed66ffae8b98ea84ee5bc34490d969286) | | (7a) |
or
![{\displaystyle C_{KHP}={\frac {m_{KHP}}{102.11g}}\pm {\sqrt {5.89516\times 10^{-11}g^{-2}\times m_{KHP}+9.591\times 10^{-13}}}{\text{M}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/33da697ce008bc8d4ae3178bf8a82cb22f9bdf9c) | | (7b) |
Data and results
Data Log
Date (dd/mm/yyyy) |
Experimenter (ID) |
Mass of KHP (g) |
Moles of KHP (mol) |
Flask Volume (mL) |
Concentration of KHP (mol/L) |
Comments
|
01/01/2011
|
AAA
|
20.0000 ± 0.0001
|
0.09793360102 ± 0.00000049
|
1000.00 ± 0.39
|
0.097934 ± 0.000019
|
This is example data. Replace it with the first completed run.
|
Conclusions
References