What\'s the expected amount of trans -[Co(NH 3 ) 4 Cl 2 ]Cl obtained by this pro

Question

What's the expected amount of trans-[Co(NH3)4Cl2]Cl obtained by this process below?

1) Set up a sand bath at 80°C.

2) Dissolve 0.5 g of ([Co(NH3)4CO3]NO3) in 2.5 mL of distilled water in a 50-mL flask

3) Heat the solution to 50-60°C in the sand bath, stirring with a magnetic stir bar. Monitor the temperature of your solution using a thermometer. Hold at 50-60°C for 3 minutes.

4) Add 1.5 mL of concentrated HCl as quickly as possible without allowing the solution to “boil” over.

5) Continue to heat the solution to 80°C for 5 mins, stirring vigorously.

Note: The temperature is critical for this step of the experiment.

6) During the heating step, a dark green precipitate should form. Cool the solution quickly by submerging it in an ice bath until it reaches room temperature, and collect the crystals by vacuum filtration.

7) Weigh a filter paper and set up the Buchner funnel again.

8) Transfer the crystals from step 6 to a 100 mL beaker and dissolve in 15 mL of ice-cold H2O, swirling briefly to dissolve any purple crystals of the cis isomer. Filter immediately, and wash the product crystals with 1 mL of ice-cold methanol. Draw air through the product crystals for several minutes, then transfer the crystals and filter paper to a watch glass and allow to air dry. Weigh your product crystals.

Explanation / Answer

The reaction is

[Co(NH3)4CO3] (NO3) + 3HCl --------------> [Co(NH3)4Cl2] (Cl) + HNO3 + H2CO3

A B

Mass of A taken = 0.5 g

Molecular mass of A = 249.06 g mol-1

Therefore no of moles = 0.5 / 249.06 = 0.002 moles = 2.00 mmoles

From stoichiometry it is seen that 1 mole A produces 1 mole B, We assume that there is enough HCl so all of A will take part in reaction.

Therefore 2 mmol A will give 2 mmol of B ideally if the conversion is 100 %

Molecular weight of B = 233.41 g mol-1

Hence mass of B that should be obtained ideally = 0.002 x 233.41 = 0.47 g

Note: we also assume that all the products formed is the required trans isomer.

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