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imported>Peter Schmitt m (→Formal definition: \cdot (or should it be \times?)) |
imported>Peter Schmitt m (→Formal definition: typographical: pH and pOH are not the product of variables) |
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pH is defined by | pH is defined by | ||
<math> pH = -\log_{10} \left[H_\mathrm{3}O^+\right] = \log_{10} \frac{1}{\left[H_\mathrm{3}O^+\right]} </math> | <math> \mathop{\rm pH} = -\log_{10} \left[H_\mathrm{3}O^+\right] = \log_{10} \frac{1}{\left[H_\mathrm{3}O^+\right]} </math> | ||
Because of [[concentration]] of hydronium ions times the concentration of hydroxide ions is constant, namely | Because of [[concentration]] of hydronium ions times the concentration of hydroxide ions is constant, namely | ||
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<math> \left(pH + pOH\right) = 14 </math> | <math> \left(\mathop{\rm pH} + \mathop{\rm pOH} \right) = 14 </math> | ||
where [[pOH]] is defined in a manner similar to pH, as shown below. | where [[pOH]] is defined in a manner similar to pH, as shown below. | ||
<math> pOH = -\log_{10} \left[OH^-\right] = \log_{10} \frac{1}{\left[OH^-\right]} </math> | <math> \mathop{\rm pOH} = -\log_{10} \left[OH^-\right] = \log_{10} \frac{1}{\left[OH^-\right]} </math> | ||
==pH of common items== | ==pH of common items== | ||
Revision as of 03:54, 4 June 2009
Potential of hydrogen (pH) is a scale that measures the acidity or alkalinity of a solution. Values for pH range usually from 0 (strongly acidic) to 14 (strongly alkaline or basic). The pH of a neutral solution, such as pure water at room temperature and atmospheric pressure, is 7, whereas the pH of an acidic solution is less than 7 and the pH of a basic solution is greater than 7. The pH scale is logarithmic, meaning that each value is 10 fold the next (for example, a pH of 12 is 10 times more basic than a pH value of 11).
Formal definition
pH is defined by
![{\displaystyle \mathop {\rm {pH}} =-\log _{10}\left[H_{\mathrm {3} }O^{+}\right]=\log _{10}{\frac {1}{\left[H_{\mathrm {3} }O^{+}\right]}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/a624f112fbea09aec4b4f5cb9fbae5bcdccf4284)
Because of concentration of hydronium ions times the concentration of hydroxide ions is constant, namely
![{\displaystyle \left[H_{\mathrm {3} }O^{+}\right]\left[OH^{-}\right]=1.0\cdot 10^{-14}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/643442f785e6232bcd382d0bb6b7a8dc79810ea4)
where pOH is defined in a manner similar to pH, as shown below.
![{\displaystyle \mathop {\rm {pOH}} =-\log _{10}\left[OH^{-}\right]=\log _{10}{\frac {1}{\left[OH^{-}\right]}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/e0e555db1801c94508361e6378d9aee12f04f147)
pH of common items
| Substances | pH range |
|---|---|
| Human gastric juice | 1 - 3 |
| Limes | 1.8 - 2.0 |
| Soft drinks | 2.0 - 4.0 |
| Lemons | 2.2 - 2.4 |
| Vinegar | 2.4 - 3.4 |
| Apples | 2.9 - 3.3 |
| Tomatoes | 4.0 - 4.4 |
| Beer | 4.0 - 5.0 |
| Bananas | 4.5 - 4.7 |
| Human urine | 4.8 - 8.4 |
| Cow's milk | 6.3 - 6.6 |
| Human saliva | 6.5 - 7.5 |
| Human blood plasma | 7.3 - 7.5 |
| Egg white | 7.6 - 8.0 |
| Milk of magnesia | 10.5 |
| Household ammonia | 11 - 12 |
References
- "General Chemistry, 2nd Ed.", pp 103-117, D. D. Ebbing & M. S. Wrighton, Houghton Mifflin, Boston, 1987.
- "General Chemistry with Qualitative Analysis, 2nd Ed.", pp. 263-278, Saunders College Publishing, Philadelphia, 1984.