All the following statements are true except

Dimethyl glyoxime is used in the detection of iron by the formation of the cherry-red complex.

The correct answer is option 4. Dimethylglyoxime is used in the detection of nickel by the formation of a cherry-red complex.

Let us break down each statement and understand why the incorrect one is incorrect:

1. The hardness of water can be estimated by using EDTA

The statement is true. EDTA (ethylenediaminetetraacetic acid) is a chelating agent used to determine water hardness. Hardness in water is primarily due to the presence of calcium \((Ca^{2+})\) and magnesium \((Mg^{2+})\) ions. EDTA forms stable complexes with these ions, and the amount of EDTA required to complex all the metal ions in a water sample can be used to quantify the hardness.

2. The hardness of water can be removed by using complex salts of sodium metaphosphate

The given statement is true. Sodium metaphosphate is used in water softening. It works by sequestering calcium and magnesium ions, which are responsible for water hardness, thereby preventing them from precipitating out as scale. This softening process is based on complexation and prevents the hardness ions from forming insoluble compounds.

3. Ziegler–Natta catalyst \((TiCl_3 + R_3Al)\) is a complex used in heterogeneous catalysis in polymerization processes

The statement is true. Ziegler–Natta catalysts are crucial in the polymerization of olefins (alkenes) to produce polymers like polyethylene and polypropylene. These catalysts often involve titanium(III) chloride \((TiCl_3)\) and an organoaluminum compound \((R_3Al)\), which work together to facilitate the polymerization process in a heterogeneous system.

4. Dimethyl glyoxime is used in the detection of iron by the formation of the cherry-red complex

The statement is false. Dimethyl glyoxime is actually used to detect nickel, not iron. It forms a cherry-red complex with nickel(II) ions, not iron. The correct reagent for detecting iron is potassium thiocyanate, which reacts with iron(III) ions to form a blood-red complex. Dimethyl glyoxime’s specificity for nickel makes it unsuitable for iron detection.

Summary

Dimethyl glyoxime reacts with nickel(II) to form a cherry-red complex, and it is not used for detecting iron. Thus, the statement about Dimethyl glyoxime being used for iron detection is incorrect.

The incorrect statement is: Dimethyl glyoxime is used in the detection of iron by the formation of the cherry-red complex.