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Question: What is the \({[OH]^ - }\) concentration of a solution with a pH of 5 at \[{25^o}C\] ?...

What is the [OH]−{[OH]^ - } concentration of a solution with a pH of 5 at 25oC{25^o}C ?

Explanation

Solution

pH is a scale used in chemistry to describe the acidity or basicity of an aqueous solution. Acidic solutions (those containing a larger concentration of H+{H^ + } ions) have a lower pH than basic or alkaline solutions. The pH scale is logarithmic, indicating the concentration of hydrogen ions in a solution in inverse order. Because the pH formula approximates the negative of the base 10 logarithm of the molar concentration of hydrogen ions in the solution, this is the case.

Complete answer:
If the electrode is calibrated in terms of hydrogen ion concentrations, it is feasible to detect the concentration of hydrogen ions directly. Titrating a solution of known concentration of a strong acid with a solution of known concentration of a strong alkaline in the presence of a reasonably high concentration of background electrolyte is one method that has been utilised frequently. Because the quantities of acid and alkali are known, calculating the concentration of hydrogen ions to connect the observed potential with concentrations is simple. Typically, a Gran plot is used to calibrate the system.
The concentration of hydroxide ions,OH−O{H^ - }, is sometimes expressed as pOH. pH readings are used to calculate pOH levels. Hydroxide ion concentration in water is proportional to hydrogen ion concentration.
At ambient temperature, pOH equals 14 - pH. However, in other cases, such as soil alkalinity measurements, this connection is not exactly valid.
We know that pH+pOH=14{\text{pH}} + {\text{pOH}} = 14
So, pOH=14−pH=14−5=9{\text{pOH}} = 14 - {\text{pH}} = 14 - 5 = 9
Also, pOH=−log⁡[OH−]=9{\text{pOH}} = - \log \left[ {{\text{O}}{{\text{H}}^ - }} \right] = {\mathbf{9}}
Hence, [OH−]=1×10−9M\left[ {{\text{O}}{{\text{H}}^ - }} \right] = 1 \times {10^{ - 9}}{\text{M}}
So, the hydroxide ion concentration of the solution is 10−9M{10^{ - 9}}{\text{M}}.

Note:
Many plants, including hibiscus, red cabbage (anthocyanin), and grapes, have pH-dependent plant pigments that can be utilised as pH monitors (red wine). Citrus juice is acidic mostly due to the presence of citric acid. Other carboxylic acids can be found in a wide range of living organisms. Lactic acid, for example, is generated by muscular action. Phosphate derivatives, such as ATP, have a pH-dependent condition of protonation. In a mechanism known as the Root effect, pH affects the activity of the oxygen-transport enzyme haemoglobin.