Which statement comparing the soap sodium stearate, and the detergent sodium lauryl sulfate is not true ?

Options

A. both form micelles in water dispersion
B. at `pH` below 6.5 the soap precipitates, the detergent does not
C. the soap is less alkaline ( basic ) than the detergent
D. calcium salts of the soap are relatively insoluble

Explanation

To determine which statement comparing the soap sodium stearate and the detergent sodium lauryl sulfate is not true, we will analyze each option provided in the question.

### Step 1: Understand the properties of sodium stearate and sodium lauryl sulfate
- **Sodium Stearate**: This is a soap that is a sodium salt of stearic acid. It has a long hydrophobic tail and a hydrophilic head, allowing it to form micelles in water.
- **Sodium Lauryl Sulfate (SLS)**: This is a synthetic detergent with a similar structure, consisting of a long hydrophobic tail and a sulfate group that is hydrophilic. It also forms micelles in water.

### Step 2: Analyze the statements
1. **Both form micelles in water dispersion**: This statement is true. Both sodium stearate and sodium lauryl sulfate can form micelles when mixed with water due to their amphiphilic nature.

2. **At pH below 6.5, the salt precipitates; the detergent does not**: This statement is also true. Sodium stearate can precipitate out of solution at lower pH levels, while sodium lauryl sulfate remains soluble.

3. **Sodium lauryl sulfate is less alkaline than sodium stearate**: This statement is not true. Sodium stearate, when hydrolyzed, can create a more alkaline solution due to the formation of carboxylate ions, making it more alkaline than sodium lauryl sulfate.

4. **Calcium salts of the soap are relatively insoluble**: This statement is true. Calcium salts of sodium stearate are indeed relatively insoluble, which is a common characteristic of soap.

### Conclusion
The statement that is not true is: **"Sodium lauryl sulfate is less alkaline than sodium stearate."**

### Final Answer
The incorrect statement is: **"Sodium lauryl sulfate is less alkaline than sodium stearate."**

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