Question

Determine the Co concentration of the solution formed when 5.00 grams of cobalt(II) nitrate hexahydrate (CO(NO3)2:6H,0) is dissolved in 550 mL of water? Select one: a. 0.0172 b. 0.0312 c. 291 d. 0.0624 O

Answer 1

Solution: The molecular weight of cobalt (11) nitrate hexahydrate (CO(NO3)2.6H20) is (58.93x1 + 2x14 + 6x16 + 12x1 + 6x16) = 290.93 g/mol Where, Atomic weight of Co = 58.93 Atomic weight of N = 14 Atomic weight of O = 16 Atomic weight of H = 1 So, if we need to calculate how many moles of sample are present in 5 gm we can calculate as follows, 290.93 gm of sample corresponds to 1 mole Or, 1 gm of sample corresponds to (1/290.93) mole Or, 5 gm of sample corresponds to (5/290.93) mole = 0.017 mole Therefore, when this 5 gm or 0.017 mole of Co(NO3)2.6H2O sample is dissolved in 550 ml or 0.55 L of water, the concentration of the dissolved sample will be, 0.017 mole -= 0.0312 mole/L = 0.0312 M 0.55 L So, the final Co2+ concentration of the dissolved sample will be 0.0312 M (option b).