Which of the following statements is false?

Options

A. `Na_(2)Cr_(2)O_(7)` is less soluble tha `K_(2)Cr_(2)O_(7)`
B. `Na_(2)Cr_(2)O_(7)` is primary standard in volumentry
C. `CrO_(4)^(2-)` is tetrahedral in shape
D. `Cr_(2)O_(7)^(2_` has a Cr-O-Cr bond

Answer

To determine which of the statements is false regarding the compounds Na2Cr2O7 and K2Cr2O7, we can analyze each statement step by step.

### Step-by-Step Solution:

1. **Analyze Statement A: Na2Cr2O7 is less soluble than K2Cr2O7.**
- Sodium (Na) and potassium (K) are both alkali metals.
- As we move down the group in the periodic table, the size of the cations increases.
- Na+ is smaller than K+, which means Na+ can be more effectively surrounded by water molecules (hydration).
- Therefore, Na2Cr2O7 is actually **more soluble** than K2Cr2O7, making Statement A **false**.

2. **Analyze Statement B: Na2Cr2O7 is a primary standard in volumetry.**
- A primary standard must have a stable composition and not absorb moisture from the air.
- Na2Cr2O7 is hygroscopic, meaning it absorbs moisture, which affects its weight and concentration.
- Thus, Na2Cr2O7 **cannot be considered a primary standard**, making Statement B **false**.

3. **Analyze Statement C: CrO4^2- is tetrahedral in shape.**
- The chromate ion (CrO4^2-) has a central chromium atom surrounded by four oxygen atoms.
- The hybridization of Cr in CrO4^2- is sp3, leading to a tetrahedral geometry.
- Therefore, Statement C is **true**.

4. **Analyze Statement D: Cr2O7^2- has a Cr-O-Cr bond.**
- The dichromate ion (Cr2O7^2-) consists of two chromium atoms connected by oxygen atoms.
- The structure indeed includes Cr-O-Cr bonds.
- Thus, Statement D is **true**.

### Conclusion:
- The false statements are **A** and **B**.

### Final Answer:
The false statements are:
- A: Na2Cr2O7 is less soluble than K2Cr2O7.
- B: Na2Cr2O7 is a primary standard in volumetry.

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