Statement Analysis for Incorrect Statement

The question asks to identify the statement that is NOT correct among the given options related to chemistry concepts.

Statement 1: Water of Crystallization Definition

This statement defines 'water of crystallization' as the fixed number of water molecules present in one formula unit of a salt. This is the standard and correct definition in chemistry. For example, copper sulfate has the formula \(CuSO_4 \cdot 5H_2O\), where 5 molecules of water are associated with each formula unit of copper sulfate. These water molecules are called water of crystallization.

Therefore, statement 1 is correct.

Statement 2: Plaster of Paris Formula

This statement claims the molecular formula of Plaster of Paris is \(CaSO_4.2H_2O\). Let's examine this:

• Plaster of Paris is chemically known as calcium sulfate hemihydrate.
• Its correct chemical formula is \(CaSO_4 \cdot \frac{1}{2}H_2O\).
• The formula \(CaSO_4 \cdot 2H_2O\) represents Gypsum, which is calcium sulfate dihydrate.

Since the formula provided in the statement (\(CaSO_4.2H_2O\)) is incorrect for Plaster of Paris, this statement is NOT correct.

Statement 3: Washing Soda and Water Hardness

This statement suggests that washing soda is used for removing the permanent hardness of water. Washing soda has the chemical formula \(Na_2CO_3 \cdot 10H_2O\). Permanent hardness in water is caused by the presence of soluble salts of calcium (\(Ca^{2+}\)) and magnesium (\(Mg^{2+}\)) ions.

When washing soda is added to hard water, sodium carbonate reacts with these soluble calcium and magnesium salts to form insoluble precipitates:

For Calcium ions: \(Na_2CO_3 (aq) + Ca^{2+}(aq) \rightarrow CaCO_3 (s) + 2Na^{+}(aq)\)

For Magnesium ions: \(Na_2CO_3 (aq) + Mg^{2+}(aq) \rightarrow MgCO_3 (s) + 2Na^{+}(aq)\)

The removal of \(Ca^{2+}\) and \(Mg^{2+}\) ions eliminates the permanent hardness. Thus, this statement is correct.

Statement 4: Venus Atmosphere Composition

This statement describes the atmosphere of Venus as being made up of thick white and yellow clouds of sulfuric acid. Scientific observations confirm that Venus has an extremely dense atmosphere composed mainly of carbon dioxide (\(CO_2\)), with clouds primarily made of sulfuric acid (\(H_2SO_4\)). These clouds are indeed thick and contribute to Venus's extreme surface temperature.

Therefore, statement 4 is correct.

Conclusion

Based on the analysis, statement 2 provides an incorrect chemical formula for Plaster of Paris. Hence, it is the statement that is NOT correct.