Consider the following reaction: When the green solid is mixed with the white solid and the colorless liquid is added, the mixture starts to bubble and fume.


Screenshot 2024 01 28 131109

Screenshot 2024 01 28 131109

Step 1 of 2

Given data: Given the reaction

CrCl3 + KCl + 2H2SO4⟶KCr(SO4)2 + 4HCl

 

Find: which substance is limiting reactant?

Explanation:

Limiting reagent is a reactant, which is completely used up in a chemical reaction.

 

Step 2 of 2

Limiting reagents are substances that are completely consumed in the completion of a chemical reaction. They are also referred to as limiting agents or limiting reactants. According to the stoichiometry of chemical reactions, a fixed amount of reactants is required for the completion of the reaction.

Let’s consider a reaction:

CrCl3 + KCl +2H2SO4 ⟶ KCr(SO4)2 + 4HCl

Stochiometric coefficient of:

CrCl3=1
KCl=1
H2SO4=2
HCl=4

In terms of weight,
CrCl3=52+35.5=158.5g

KCl=39+35.5=74.5g
H2SO4=2×(2×1+32+4×16)=196g
KCr(SO4)2=39+52+2(32+4×16)=283g
4HCl=4(1+35.5)=146g

In the given reaction

CrCl3​ + KCl + 2H2​SO4 ​⟶ KCr(SO4​)2 + 4HCl

Chromium chloride (CrCl3​) reacts with potassium chloride (KCl) and sulfuric acid (2H2​SO4​) to produce potassium chromium sulfate (KCr(SO4​)2​) and hydrochloric acid (4HCl).

 

Let’s use the color change in this reaction to determine the limiting reagent:

  1. Prepare Solutions:
    • Prepare solutions of CrCl3​,KCl,and 2H2​SO4​ with known concentrations.
    • Mix the solutions in a reaction vessel.

 

  1. Observe Color Change:
    • Chromium chloride (CrCl3​) often has a characteristic color (green or violet, depending on the oxidation state of chromium).
    • As the reaction proceeds, one of the reactants will be consumed.

 

  1. Color Changes:
    • If CrCl3​ is in excess, the characteristic color will persist.
    • If CrCl3​ ​ is the limiting reagent, its color will gradually disappear.

 

  1. Color Disappearance:
    • If KCl is the limiting reagent, CrCl3​ will react completely, and its color will disappear.

Hence, Here limiting reagent is CrCl3​

Explanation:

  • The reagent that determines the extent of the reaction and is completely consumed is the limiting reagent.
  • If the color disappears, CrCl3​ is limiting.
  • If the color remains, KCl is limiting.

 

Final solution

This method allows students to visually identify the limiting reagent based on the color change in the reaction mixture. If they observe the disappearance of the characteristic color of CrCl3​, they can conclude that CrCl3​ is limiting. If the color persists, KCl is limiting.

Therefore, we can conclude that CrCl3 is the limiting reagent.

 

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