Water containing calcium bicarbonate produces ______ with soap.

Explanation

To solve the question "Water containing calcium bicarbonate produces ______ with soap," we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Components**:
- We need to understand what calcium bicarbonate is and how it behaves in water. Calcium bicarbonate (Ca(HCO₃)₂) is a soluble salt that dissociates in water to release calcium ions (Ca²⁺) and bicarbonate ions (HCO₃⁻).

2. **Understand the Reaction with Soap**:
- Soap is typically a sodium or potassium salt of fatty acids. When soap is added to water containing calcium ions, a reaction occurs.

3. **Formation of Scum**:
- The calcium ions (Ca²⁺) from the dissolved calcium bicarbonate react with the soap to form an insoluble compound. This insoluble compound is known as scum. Scum is a precipitate that forms when the calcium ions interact with the fatty acids in the soap.

4. **Conclusion**:
- Therefore, when water containing calcium bicarbonate is treated with soap, it produces scum.

### Final Answer:
Water containing calcium bicarbonate produces **scum** with soap.

---