JEE Main 2023 · 10 April · evening · Single correct · +4 / −1
Ferric chloride is applied to stop bleeding because -
- (a) FeCl₃ reacts with the constituents of blood which is a positively charged sol.
- (b) Blood absorbs FeCl₃ and forms a complex.
- (c) Cl⁻ ions cause coagulation of blood.
- (d) Fe³⁺ ions coagulate blood which is a negatively charged sol.
Answer and solution
Answer (d) Fe³⁺ ions coagulate blood which is a negatively charged sol.
Solution
Chemistry ma’am · 4 steps
Blood is a negative sol, so look for the positive ion: Fe³⁺ does the coagulating.
- Charge on blood. Blood is a colloidal sol whose particles carry a negative charge. Like charges repel, so the particles stay dispersed and blood keeps flowing.
- Which ion acts. A sol is coagulated by the ion with the opposite charge to its particles. For a negative sol that is the cation, so in FeCl₃ it is Fe³⁺, not Cl⁻.
- Why it works fast. By the Hardy–Schulze rule, a higher charge on the coagulating ion means stronger coagulation. A +3 ion neutralises the negative particles quickly, they clump into a clot, and bleeding stops.
- So. Fe³⁺ ions coagulate blood, which is a negatively charged sol. The answer is (d).
The idea to keep. To coagulate a sol, use the ion with the opposite charge, and the higher its charge, the better. Negative sols like blood need cations; Fe³⁺ and Al³⁺ work very well.
Answer from the NTA final answer key. Solution by PrepWiser.