Question

weighed watch glass and record the mass of the product. Write a balanced equation for the synthesis and hence calculate the percentage yield (based on the mass of the nickel(II) chloride hexahydrate used) and record it, with working, in the lab notebook.

Answer 1

There are two reactions involved in this process:

$NiCl_{2}\cdot 6H_{2}O+6NH_{3}\rightarrow [Ni(NH_{3})_{6}]Cl_{2}+6H_{2}O$

$[Ni(NH_{3})_{6}]Cl_{2}+2NaBF_{4}\rightarrow [Ni(NH_{3})_{6}][BF_{4}]_{2}+2NaCl$

So, in the total process, we obtain one moles of product per each mole of NiCl₂.6H₂O that was originally added. In order to calculate the percentage yield you will need to use the mass of product you obtained. To do this, you first need to calculate the number of moles of NiCl₂.6H₂O that you originally added for the reaction:

$n=\frac{m}{m_{molar}}=\frac{1.5g}{237.7g/mol}=0.0063moles$

And this is the number of moles of product you would obtain if all of the reactant in fact reacted. This would mean a mass of product of:

$m=n\cdot m_{molar}=0.0063moles\cdot 334.5g/mol=2.11g$

The percentage yield can now be calculated as the quotient between the mass you obtained from your reaction and this theoretical value, multiplied by 100:

$yield=100\cdot \frac{m_{obtained}}{2.11g}$