Understanding the pH scale is key to solving this problem. The pH value indicates the acidity or alkalinity of a solution.
pH Scale Basics
- The pH scale typically ranges from 0 to 14.
- A pH of 7 is considered neutral.
- A pH less than 7 indicates an acidic solution.
- A pH greater than 7 indicates a basic (alkaline) solution.
pH and Ion Concentrations
The pH value is directly related to the concentration of hydrogen ions ($H^+$) and hydroxide ions ($OH^-$) in a solution.
- Relationship with $H^+$ Ions: pH is defined as the negative logarithm (base 10) of the hydrogen ion concentration:
$ pH = -\log_{10}[H^+] $
This means that as the pH value increases, the concentration of $H^+$ ions ($[H^+]$) decreases. - Relationship with $OH^-$ Ions: In aqueous solutions, the product of hydrogen ion and hydroxide ion concentrations is constant ($K_w = [H^+][OH^-] = 1 \times 10^{-14}$ at 25°C). This leads to the relationship:
$ pH + pOH = 14 $
where $pOH = -\log_{10}[OH^-]$. As the pH value increases, the pOH decreases, which in turn means the concentration of $OH^-$ ions ($[OH^-]$) increases.
Interpreting pH Increase from 7 to 14
An increase in pH from 7 to 14 signifies a shift from a neutral solution towards a highly basic (alkaline) solution.
- At pH 7 (Neutral): $[H^+] = [OH^-] = 1 \times 10^{-7}$ M.
- At pH 14 (Highly Basic): This corresponds to a pOH of 0 ($14 - 14 = 0$). Therefore, $[OH^-] = 10^0 = 1$ M, and $[H^+] = 10^{-14}$ M.
Comparing pH 7 and pH 14:
- The $H^+$ ion concentration decreases significantly (from $10^{-7}$ M to $10^{-14}$ M).
- The $OH^-$ ion concentration increases significantly (from $10^{-7}$ M to $1$ M).
Therefore, an increase in pH value from 7 to 14 represents an increase in the $OH^-$ ion concentration.
Similar Questions
- Which of the following statements is/are true or false?
Statements:
A) H$_2$SO$_4$ is used in the refining of petroleum to remove sulphur and other compounds.
B) The basic nature of Sodium Hydroxide (NaOH) is due to the presence of Hydrogen ions in the solution.
Important Questions from Acids, Bases & Salts
When a large amount of carbon dioxide dissolves in a water body, the water becomes acidic because of the formation of which of the following acids?
Which one of the following oxides is a neutral oxide?
- Which of the following solutions is slightly acidic due to hydrolysis?
- Which of the following foods would you advise to neutralise excess stomach acids?
- What is the primary contributor to the sour taste in foods like lemons, vinegar and yoghurt?
