In the laboratory preparation of nitric acid, the mixture of concentrated sulphuric acid and sodium nitrate should not be heated very strongly above `200^@C`. Give reasons. 

Explanation

To answer the question regarding why the mixture of concentrated sulfuric acid and sodium nitrate should not be heated very strongly above 200°C during the laboratory preparation of nitric acid, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Understanding the Reaction**:
- The laboratory preparation of nitric acid involves the reaction between sodium nitrate (NaNO3) and concentrated sulfuric acid (H2SO4).
- The primary reaction at temperatures below 200°C is:
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