Problem 68 - A Complete Resource Book in Chemistry for JEE Main

Question

Latex can be coagulated with? (a) \(\mathrm{CH}_{3} \mathrm{COOH}\) (b) \(\mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{CH}_{3} \mathrm{OH}\) (d) All of these

Step-by-Step Solution

Answer

Latex can be coagulated with \( \mathrm{CH_3 COOH} \).

Step 1: Understanding the Question

We need to determine which substance is capable of coagulating latex from the given options: acetic acid \( \mathrm{(CH_3 COOH)} \), water \( \mathrm{(H_2 O)} \), methanol \( \mathrm{(CH_3 OH)} \), or all of these.

Step 2: Analyzing Latex Coagulation

Latex is a colloidal suspension which can be coagulated by adding acidic substances. Acetic acid \( \mathrm{(CH_3 COOH)} \) is a weak acid, which is known to coagulate latex by neutralizing its charges.

Step 3: Assessing Options

- Option (a): Acetic acid \( \mathrm{(CH_3 COOH)} \) can coagulate latex. - Option (b): Water \( \mathrm{(H_2 O)} \) does not generally coagulate latex as it is neutral. - Option (c): Methanol \( \mathrm{(CH_3 OH)} \) typically does not cause coagulation since it's an alcohol, not an acid.Therefore, option (a) is the correct choice.

Step 4: Conclusion

Latex is coagulated by the addition of acetic acid, which neutralizes charge repulsions among latex particles.

Key Concepts

Colloidal Suspension

A colloidal suspension is a mixture where tiny particles are dispersed uniformly throughout another substance without dissolving in it. These particles are called colloids, and they range in size from 1 nm to 1 µm. In a colloidal suspension, the colloids remain distributed due to the balance of forces acting on them. One aspect of this balance is the electric charge on the particle's surface, which keeps the particles from clumping together.

Latex is a prime example of a colloidal suspension. It consists of rubber particles suspended in water. The rubber particles are small enough to stay suspended, and they carry an electric charge. This charge creates repulsion between the particles, preventing them from aggregating and keeping the latex stable in its liquid form.

• Particles typically range from 1 nm to 1 µm.
• Key properties include electric charge and uniform distribution.
• Example: latex consists of rubber particles in water.

Acetic Acid

Acetic acid, with the chemical formula \( \mathrm{CH_3COOH} \), is a weak acid commonly found in vinegar. It plays a significant role in the coagulation of colloidal suspensions like latex.

Even though it is termed a "weak" acid, acetic acid can still donate protons (\( \mathrm{H^+} \)) to a solution. These protons can interact with the charged surfaces of colloidal particles. Specifically, in the case of latex, acetic acid donates its \( \mathrm{H^+} \) ions to the negatively charged rubber particles, neutralizing some of the charge. This neutralization reduces the repulsive forces between the latex particles, assisting them to come together and form clumps, a key step in coagulation.

• Has the formula: \( \mathrm{CH_3COOH} \).
• Commonly associated with vinegar.
• Donates protons to neutralize charges in latex.

Neutralization of Charge

The neutralization of charge is a critical concept in understanding how coagulation in colloidal suspensions works. When particles in a suspension have the same type of charge, they repel each other, maintaining separation. Neutralization of charge involves adding substances that reduce or eliminate this charge, allowing particles to come closer and form aggregates.

In latex, the rubber particles carry negative charges on their surfaces. Acetic acid provides \( \mathrm{H^+} \) ions, which bond with these negative charges, effectively reducing the repulsive forces. As a result, the particles can approach each other and coagulate. This process is an excellent example of how adjusting charges in a colloidal system can lead to a phase transition from liquid to solid.

• Involves reducing particle surface charges.
• Allows particles to clump together.
• In latex, achieved using acetic acid's \( \mathrm{H^+} \) ions.