Sulfuric acid and Potassium hydroxide Reaction | H2SO4 + KOH

Sulfuric acid (H2SO4) reacts with Potassium hydroxide (KOH) gives potassium sulfate (K2SO4) and water (H2O) as products. Heat is released due to neutralization of a strong acid (H2SO4) and a strong base (KOH).

In this tutorial, we will discuss followings.

Balanced reaction of H2SO4 and KOH

H2SO4 + 2KOH(aq) → K2SO4(aq) + 2H2O(l)

One mole of H2SO4 reacts with two moles of KOH. As products, one mole of K2SO4 and two moles of H2O are given.

balanced reaction of potassium hydroxide sulfuric acid KOH + H2SO4 reaction

Reactants of reaction

Potassium hydroxide (KOH)

Potassium hydroxide is a white solid at room temperature and readily soluble in water. Aqueous Potassium hydroxide solution is a strong base because it completely dissociates to K+ and OH- ions in water as below. Due to strong basic characteristics, aqueous KOH should show pH values much higher than 7.

KOH(aq) → K+(aq) + OH-(aq)

Sulfuric acid (H2SO4)

Sulfuric acid is a strong acid because it completely dissociates to H+ and SO42- ions in water. These sulfuric acid solutions should show pH values much lower than 7 due to its strong acidic nature.

H2SO4(aq) → 2H+(aq) + SO42-(aq)

Products of reaction

Potassium sulfate (K2SO4

Potassium sulfate is a salt and soluble in water to form a colourless aqueous solution. An aqueous solution which contains only K2SO4 as a salt, is a neutral solution.

K2SO4(aq) → 2K+(aq) + SO42-(aq)

Heat generation when H2SO4 and KOH are neutralized

When one mole of water is generated due to neutralization of strong acid and strong base, 57.1kJ is released. Because two moles of water are generated according to the above stoichiometric balanced equation, -114.2 kJ (57.1 kJ mol-1* 2 mol) kJ is released when H2SO4 is neutralized by KOH.

Change of oxidation numbers

This reaction is not a redox reaction because oxidation numbers of atoms are not changed during the reaction.

  • Potassium's only oxidation state is +1. In both KOH and K2SO4, potassium is at +1 oxidation state.
  • Sulfur's oxidation number in H2SO4 is +6. And also, on KSO4, oxidation number of sulfur is +6.

Physical and chemical observation of H2SO4 and KOH reaction

Here, we will see some physical observations and chemical properties changes during the reaction.

Colour and physical state changes

  • Both aqueous H2SO4 and aqueous KOH are colourless aqueous solutions.
  • K2SO4 which is given as a product is readily soluble in water and give a colourless aqueous solution.

pH change

  • Reactants: KOH is a strong base and show pH value higher than 7 and H2SO4 is strong acid and should show pH value less than 7.
  • Products: K2SO4 is a salt. Both K+ and SO42- ions are stable in water and do not participating in hydrolysis reactions. If all H2SO4 and KOH are completely reacted with each other, pH of final solution should be 7.

Safety and health hazards possible of H2SO4, KOH and K2SO4

  • H2SO4: Causes severe skin burns,cause eye damages
  • KOH: Harmful if swallowed, severe skin burns (skin corrosion and irritation) and eye damage
  • K2SO4: Corrosive, serious eye damage, eye irritation,
  • Heat generation: Due to generation of large heat in a short time period, be careful to not touch beaker or other where reaction is being happened.


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