15 Facts on H2SO4 + K2Cr2O7: What, How To Balance & FAQs

by

Chemical reactions involve dynamic breaking of reactants and formation of respective products. Let us study about the chemical reactions involved in H2SO4 and K2Cr2O7.

The reaction between H2SO4 and K2Cr2O7 is termed as redox (reduction-oxidation) reaction. Sulphuric acid is a strong, oxidizing acid with dehydrating properties. Potassium dichromate is a common analytical reagent, used as oxidising agent in lab and industrial applications.

Here in the following article we explain the mechanisms of the reactions involved.

What is the product of H2SO4 and K2Cr2O7?

Sulphates of potassium and chromium together with oxygen and water are liberated when sulphuric acid reacts with potassium dichromate.

2K2Cr2O7 + 8H2SO4 = 2K2SO4 + 2Cr2(SO4)3 + 8H2O + 3O2

What type of reaction is H2SO4 + K2Cr2O7?

H2SO4 + K2Cr2O7 is redox reaction which is followed by neutralization reaction to form salts and water.  

How to balance H2SO4 + K2Cr2O7?

We can balance the reaction

K2Cr2O7 + H2SO4 = K2SO4 + Cr2(SO4)3 + H2O + O2 using following algebraic method,

  • Step 1- Each reactant or product in the equation is labeled with a variable (A, B, C, D, E, and F) to represent unknown coefficients.
  • A 2K2Cr2O7 + B 8H2SO4 = C 2K2SO4 + D 2Cr2(SO4)3 + E 8H2O + F 3O2
  • Step 2 – Now, the equation is solved by an appropriate number, considered to be the coefficient of reactants and products.
  • K = 2A = 2C, Cr = 2A = 2D, O = 7A + 4B = 4C + 12D + E + 2F, H = 2B = 2E, S = B = C + 3D
  • Step 3- All variables and coefficients are calculated by the Gaussian elimination method, and finally, we obtain
  • A = 2, B = 8, C = 2, D = 2, E = 8 and F = 3
  • So, the overall balanced equation is,
  • 2K2Cr2O7 + 8H2SO4 = 2K2SO4 + 2Cr2(SO4)3 + 8H2O + 3O2

H2SO4 + K2Cr2O7 titration

K2Cr2O7 + H2SO4 system is an example of redox titration where standard solution of potassium dichromate is used for further analysis. Several apparatus, conditions, and procedures for the titration are discussed below:

Apparatus used

Graduated burette, burette clamps, volumetric flask, conical flask, and beakers.

Indicator

Sodium diphenylamine sulfonate serves as an indicator.

Procedure

  • K2Cr2O7 is dissolved in distilled water to prepare the standard solution in a volumetric flask.
  • An unknown solution of Fe+2 is pipetted out in a flask.
  • To the flask containing unknown solution H2SO4 is added.
  • Then after phosphoric acid solution and sodium diphenylamine sulfonate indicator is added to the flask.
  • The flask is swirled gently to mix the contents.
  • Fill the burette with K2Cr2O7 and record the initial reading on the burette.
  • Titrate the iron solution present in the flask.
  • The intense purple colour produced later on adding the excessive drop of K2Cr2O7 marks the endpoint of the analysis.
  • The final value of the volume is determined using the calibration scale of the burette.
  • Repeat the process in triplicate to record concordant readings.
  • The strength of the solution can be calculated using the formulae
  • S2 = (V1 * S1)/V2 where S2 is the strength of the acid, V1 is the volume of base added, and S1 is the strength of the base and V2 is the volume of the acid used.

H2SO4 + K2Cr2O7 net ionic equation

The net ionic equation of H2SO4 + K2Cr2O7 is

H+ (aq) + Cr2O7-2 (aq) + 3SO4-2 (aq) +8H+ (aq) = 2Cr+3 (aq) + 2K+ (aq) + 2SO4-2 (aq)

The following steps are used to derive the net ionic equation:

  • Firstly, write the balanced chemical equation and represent the physical states of reactants and products
  • 2K2Cr2O7 (aq) + 8H2SO4 (l) = 2K2SO4 (aq) + 2Cr2(SO4)3 (aq) + 8H2O (l) + 3O2 (g)
  • Now, strong acids, bases and salts dissociate into ions whereas pure solid substances and molecules do not dissociate
  • Cr2O7-2 (aq) + 3SO4-2 (aq) +8H+ (aq) = 2Cr+3 (aq) + 2K+ (aq) + 2SO4-2 (aq)

H2SO4 + K2Cr2O7 conjugate pairs

  • H2SO4 will form conjugate base by losing a proton i.e., HSO4–
  • Conjugate pair do not exist for K2Cr2O7 as it do not contain proton.

H2SO4 and K2Cr2O7 intermolecular forces

H2SO4 + K2Cr2O7 reaction enthalpy

The reaction enthalpy of H2SO4 + K2Cr2O7 is -85.9 kJ/mol.

Is H2SO4 + K2Cr2O7 a buffer solution?

H2SO4 + K2Cr2O7 do not form a buffer solution because neither a strong acid (H2SO4) nor a reagent (K2Cr2O7) can be a part of buffer.

Is H2SO4 + K2Cr2O7 a complete reaction?

H2SO4 + K2Cr2O7 is a complete reaction as stable products namely potassium sulphate, chromium sulphate, water and carbon dioxide are formed on the right-hand side after the equilibrium is reached.

Is H2SO4 + K2Cr2O7 an exothermic or endothermic reaction?

H2SO4 + K2Cr2O7 reaction is exothermic reaction because the enthalpy of the reaction is calculated to be negative.

Is H2SO4 + K2Cr2O7 a redox reaction?

H2SO4 + K2Cr2O7 is an example of redox reaction where

  • Reduction reaction 4Cr+6 + 12 e– = 4 Cr+3
  • Oxidation reaction 6 O-2 = 6O0 + 12 e–

Is H2SO4 + K2Cr2O7 a precipitation reaction?

H2SO4 + K2Cr2O7 is not a precipitation reaction as no precipitates are observed at the end of the reactions.

Is H2SO4 + K2Cr2O7 reversible or irreversible reaction?

H2SO4 + K2Cr2O7 is irreversible reaction because no products formed in the reaction converts back into the reactants.

Is H2SO4 + K2Cr2O7 displacement reaction?

H2SO4 + K2Cr2O7 is not a displacement reaction as no displacements of molecules from the reactants were noticed.

Conclusions

The reaction of sulphuric acid with potassium dichromate produces an important sulphate salt of potassium and chromate. The sulphate salts of chromium and potassium are used as photography hardener and as leather tanning.