How to Calculate pH of Salts Using Hydrolysis Formula and Acid Base Strength
Salt is a compound which is formed by the neutralisation reaction between an acid and a base. They ionise in water producing cations and anions, which either exist as hydrated ions in aqueous solutions or mix with water to regenerate the acids and bases. The three kinds of salts depending on their pH value are:
1. Neutral Salts: pH value 7.
2. Acidic Salts: The pH less than 7.
3. Basic Salts: The pH more than 7.
The pH value measures the level of acidity or alkalinity in a water-soluble solution. The scale measures from 0 to 14. Anything lower than 7 is acidic and anything higher than 7 is basic. The calculation of acidity or alkalinity of a solution is known as pH, the relative quantity is stated by pH. Acidity depends on the concentration of the hydrogen ions and if its concentration is more then more is the acidity of the solution. So the meaning of pH is justified as the power of hydrogen.
pH Value of Sodium Chloride
Sodium chloride is an ionic compound which represents a 1:1 ratio of sodium and chloride ions. Sodium chloride is responsible for the salinity of seawater. The pH of sodium chloride remains at seven due to the weak basicity of chloride ions. It is formed from the reaction of a strong acid and a strong base, in the formation hydrogen chloride is neutralised by sodium hydroxide.
When sodium chloride is mixed with water it will not show any acidic or basic properties, as both ions are not susceptible to hydrolysis. Brine is water saturated with salt or a solution of sodium chloride and water which occurs naturally on the earth's surface or in the benthic zone of oceans.
pH of Salt of Weak Acid and Strong Base
Salts from strong bases and weak acids have a pH greater than seven, the anion being from the weak acid, accepting the proton from the water in the chemical reaction.
KCN(s) → K+(aq) + CN−(aq)
CN−(aq) + H2O(l) ⇌ HCN(aq) + OH−(aq)
Ammonium chloride is an acidic salt as it is a salt of strong acid namely hydrochloric acid, and a weak base which is ammonium hydroxide, another example is sodium acetate which is salt in solid state and can't be used in liquid form as an acid or base.
Sodium hydroxide is a strong base and acetic acid is a weak acid, so the sodium salt is called sodium acetate. It is in white granular powder form, hygroscopic in nature as it easily absorbs water, medically it is used intravenously as an electrolyte for sodium level correction in hyponatremic patients.
pH of Salts List
Most of the salts have pH values less than or more than 7. This means they may be neutral, acidic or basic.
1. Sodium chloride, pH is 7 and the nature of the salt is neutral.
2. Sodium carbonate, pH is ~11 and nature is basic.
3. Ammonium chloride, pH is ~6 and nature is acidic.
4. Potassium sulphate, pH is 7 and nature is neutral.
5. Ammonium sulphate, pH is ~5.5 and the nature is acidic.
6. Potassium chloride, pH is 7 and nature is neutral.
7. Ammonium carbonate, pH is ~7.8, and nature is slightly basic.
8. Sodium sulphate, pH is 7, nature is neutral.
Interesting Facts
Basic salts such as sodium carbonate are used to maintain soil acidic pH.
Even if we put a teaspoon of table salt in a glass of pure water, it won't change its pH. Pure water has a pH value of 7.
Key Features of pH of Salts
Salt is a compound which is formed by the neutralisation reaction between an acid and a base.
The pH value measures the level of acidity or alkalinity in water-soluble solution.
Salts from strong bases and weak acids do not hydrolyze and they have a pH greater than 7.
FAQs on pH of Salts and Their Acidic Basic or Neutral Nature
1. What is the pH of salts?
The pH of salts is the measure of acidity or basicity of a salt solution formed from the reaction of an acid and a base. When a salt dissolves in water, its ions may react with water in a process called hydrolysis, which can produce H3O+ or OH- ions.
- If the salt is from a strong acid and strong base, pH ≈ 7 (neutral).
- If from a strong acid and weak base, pH < 7 (acidic).
- If from a weak acid and strong base, pH > 7 (basic).
2. Why are some salts acidic, basic, or neutral?
Some salts are acidic, basic, or neutral because their ions undergo hydrolysis in water depending on the strength of the parent acid and base.
- Strong acid + Strong base → Neutral salt (e.g., NaCl).
- Strong acid + Weak base → Acidic salt (e.g., NH4Cl).
- Weak acid + Strong base → Basic salt (e.g., CH3COONa).
3. How do you calculate the pH of a salt formed from a strong acid and strong base?
The pH of a salt formed from a strong acid and strong base is 7 at 25°C because neither ion undergoes hydrolysis. For example:
- NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)
- NaCl dissociates as: NaCl(aq) → Na+(aq) + Cl-(aq)
4. How do you calculate the pH of a salt of a weak acid and strong base?
The pH of a salt of a weak acid and strong base is greater than 7 and is calculated using Kb of the conjugate base. Example: CH3COONa.
- CH3COO-(aq) + H2O(l) ⇌ CH3COOH(aq) + OH-(aq)
- Kb = Kw / Ka
- [OH-] = √(Kb × C)
5. How do you calculate the pH of a salt of a strong acid and weak base?
The pH of a salt of a strong acid and weak base is less than 7 and is calculated using Ka of the conjugate acid. Example: NH4Cl.
- NH4+(aq) + H2O(l) ⇌ NH3(aq) + H3O+(aq)
- Ka = Kw / Kb
- [H3O+] = √(Ka × C)
6. What is salt hydrolysis?
Salt hydrolysis is the reaction of salt ions with water to produce an acidic or basic solution. During hydrolysis, the conjugate acid or base reacts with water to form H3O+ or OH- ions.
- Example (basic hydrolysis): CH3COO- + H2O ⇌ CH3COOH + OH-
- Example (acidic hydrolysis): NH4+ + H2O ⇌ NH3 + H3O+
7. What is the formula for the pH of a salt of a weak acid and weak base?
The pH of a salt formed from a weak acid and weak base is given by pH = 7 + ½ log(Ka/Kb). This formula shows:
- If Ka = Kb, pH = 7 (neutral).
- If Ka > Kb, solution is acidic.
- If Kb > Ka, solution is basic.
8. What is the pH of ammonium chloride (NH4Cl)?
The pH of NH4Cl solution is less than 7 because it is a salt of a strong acid (HCl) and weak base (NH3). In water:
- NH4Cl(aq) → NH4+(aq) + Cl-(aq)
- NH4+ + H2O ⇌ NH3 + H3O+
9. What is the pH of sodium acetate (CH3COONa)?
The pH of CH3COONa solution is greater than 7 because it is a salt of a weak acid (CH3COOH) and strong base (NaOH). In water:
- CH3COONa(aq) → CH3COO-(aq) + Na+(aq)
- CH3COO- + H2O ⇌ CH3COOH + OH-
10. How does the strength of acid and base affect the pH of a salt?
The strength of the parent acid and base determines whether the salt solution is acidic, basic, or neutral.
- Strong acid + Strong base → Neutral salt (pH = 7).
- Strong acid + Weak base → Acidic salt (pH < 7).
- Weak acid + Strong base → Basic salt (pH > 7).
- Weak acid + Weak base → Depends on relative Ka and Kb.
