Question

Separation of a Mixture – Pre lab 1. Where do you find in nature the three components that we will separate in this lab? What are they used for? (hint - an internet search is helpful) 2. If a student started with 4.2 grams of the mixture and recovered .75 g NaCl; 1.35 g SiO2; and .24 g CaCO3 what was the percent yield? 3. Think of a way in which physical separations are used in our world and describe that process in great detail.

Answer 1

1. In nature, we can find the chalk powder, which contains a mixture of NaCl, SiO₂ and CaCO₃.

2. The total mass of mixture = 4.2 g

The recovered mass of NaCl = 0.75 g

The recovered mass of SiO2 = 1.35 g

The recovered mass of CaCO₃ = 0.24 g

The total mass recovered = 0.75 + 1.35 + 0.24, i.e. 2.34 g

Hence, the percent yield = (recovered mass/total mass)*100

= (2.34/4.2)*100, i.e. 55.71%

3. The physical methods for separation of NaCl, SiO₂ and CaCO₃ can be described as follows.

1. Filtration: If you add water into the mixture of NaCl, SiO₂ and CaCO₃, only NaCl dissolves in water, whereas the other two do not. Then filter the solution, evaporate/crystallize the filtrate to recover the solid NaCl, whereas the residue contains a mixture of SiO₂ and CaCO₃.

Note: The separation of NaCl is possible due to the difference in the physical property, i.e. solubility.

2. Decanting: If you add water into the mixture of SiO₂ and CaCO₃, and shake for some time, SiO₂ immediately settles down, whereas CaCO₃ slowly settles down. Then decant the solution before CaCO₃ settles down. Repeat this process 5 to 6 times, the decanted water contains all the CaCO₃ from the mixture, while the residue is pure SiO₂. Allow the decanted water until all the CaCO₃ settles down, then simply decant all the water to get solid CaCO₃.

Note: The separation of SiO₂ and CaCO₃ is possible due to the difference in the physical property, i.e. density. (density_CaCO3 < density_SiO2)