GATE 2021 CY – Question 65

Inorganic Chemistry · Main Group Elements: Shapes and structures of molecules using VSEPR postulates, Hydrides, halides, oxides, oxoacids, nitrides, sulfides - shapes and reactivity. Structure and bonding of boranes, carboranes, silicones, silicates, boron nitride, borazine and phosphazenes: electron counting in polyhedral boranes, isolobal analogy. Allotropes of carbon, phosphorus and sulfur. Industrial synthesis of compounds of main group elements such as NH3, H2SO4 and HNO3. Chemistry of noble gases and interhalogen compounds. Acid-base concepts and principles (Lewis, Brønsted, HSAB and acid-base catalysis). · 2 marks · Numerical answer

The quantity of cobalt ore $Co_3(AsO_4)_2\cdot H_2O$ needed to obtain 1 kg Co is ______ kg (two decimal places). Atomic weights: Co 59, As 75, O 16, H 1.

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Correct answer: 2.50 to 2.80

Explanation

The formula mass of Co3(AsO4)2·H2O is 3×59+2×(75+4×16)+18=473 g/mol. Each mole contains 177 g cobalt, so the cobalt mass fraction is 177/473. To obtain 1 kg cobalt requires 473/177=2.6723 kg ore, or **2.67 kg** to two decimals, assuming quantitative recovery.