Gold numbers of protective colloids A, B, C and D are 0.50, 0.01, 0.10 and 0.005, respectively. The

Q: What exactly is a Gold Number?

It is the minimum mass (in mg) of a protective lyophilic colloid needed to prevent the coagulation of 10 mL of a standard red gold sol when 1 mL of 10% NaCl is added.

Q: Why is the relation inversely proportional?

Because a highly effective protective colloid will require only a very small quantity (low gold number) to provide the same level of protection as a larger quantity of a weaker colloid.

Q: Does a high gold number mean it's a good protective colloid?

No, it's the exact opposite! A high gold number means you need a lot of it to protect the sol, which implies it is a weak protective colloid.

Q: Who introduced the concept of Gold Number?

The concept was introduced by Richard Zsigmondy in 1901 to quantify the protective power of lyophilic colloids.

Q: What is the standard sol used in this definition?

A standard red gold sol is used. When it coagulates, its color changes from red to blue, making it a perfect visual indicator for the test.

Question

Gold numbers of protective colloids $A$, $B$, $C$ and $D$ are $0.50$, $0.01$, $0.10$ and $0.005$, respectively. The correct order of their protective powers is

Options:

(A) $D < A < C < B$

(B) $C < B < D < A$

(C) $A < C < B < D$

(D) $B < D < A < C$

Sigma Percentile · Accepted Answer

### The Threat to Gold Sols Imagine you have a beautiful, red-colored gold sol. It is a lyophobic colloid, meaning it hates the solvent and is highly unstable. If you add even a tiny pinch of an electrolyte like sodium chloride, the gold particles will clump together and coagulate. The beautiful red color will turn blue and settle down, which is a disaster! To protect this gold sol from coagulating, we add a 'bodyguard'—a lyophilic (solvent-loving) colloid. This bodyguard surrounds the gold particles, forming a protective layer. ### The Concept of Gold Number But how do we measure which bodyguard is the strongest? In 1901, Richard Zsigmondy introduced a brilliant metric called the **Gold Number**. He defined it as the minimum mass (in milligrams) of the protective colloid that must be added to 10 mL of a standard red gold sol to prevent it from turning blue when 1 mL of 10% NaCl solution is added. Think about this definition carefully. If a bodyguard is incredibly strong, you only need a tiny amount of it to protect the gold sol. If it is weak, you will need a lot of it. Therefore, the **Protective Power** is inversely proportional to the **Gold Number**. $$ ext{Protective Power} \propto \frac{1}{ ext{Gold Number}} $$ ### Analyzing the Given Colloids In our problem, we are given four colloids with their respective gold numbers: - $A = 0.50$ - $B = 0.01$ - $C = 0.10$ - $D = 0.005$ Let us arrange them by their gold numbers from highest to lowest: $$ A (0.50) > C (0.10) > B (0.01) > D (0.005) $$ ### Final Calculation Since a smaller gold number means a stronger protective power, we simply reverse the order to find their protective strengths. $$ A < C < B < D $$ Colloid $D$, having the smallest gold number, is the ultimate champion, while $A$ is the weakest. Thus, the correct option is **(c)**.

Animated Solution for Chemistry - Surface Chemistry: Gold numbers of protective colloids $A$ , $B$ , $C$ and $D$ are $0.50$ , $0.01$ , $0.10$ and $0.005$ , respectively. The correct order of their protective powers is

Select Answer:

Visualized Solution

Given Data

Concept of Gold Number

Ordering Gold Numbers

Ordering Protective Powers

Final Answer

The Sigma Insight: Colloids, Micelles and and Emulsions

The Threat to Gold Sols

The Concept of Gold Number

Analyzing the Given Colloids

Final Calculation

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