Gravimetric Analysis of Metal Carbonate

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Li2CO3: 81.21%

Na2CO3: 56.61 %

K2CO3: 43.41 %

Rb2CO3: 25.97%

- What alkali metal is present in the unknown based upon:

A The percentage of carbonate in the unknown:

B The color of the flame?

Explain your reasoning:

By using the 40.6 % experimental percent, I subtracted that from 100 to get 59.4%, which is closest to sodium. When we burned the unknown, it turned a shade of yellow, which confirms that it is sodium (according to numerous online sources too).

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Analysis of Errors:

1

- Show, by calculation, that the addition of 60 mL of .20 M SrCl2 is in excess and that the unknown alkali metal carbonate is the limiting reagent.

There is enough Sr to use all the CO3, but there isn’t enough CO3 to use all the Sr. This means that the Sr is the excess and the CO3 is the limiting reagent.

- Why is it necessary to add the SrCl2 in excess?

The importance of the SrCl2 as the excess is great because without it, there wouldn’t be enough to use all the CO3, making it a limited reagent instead.

- What would be the effect on the experimental percent of carbonate in the unknown had the SrCl2 been the limiting reagent.

This scenario would yield a lower experimental percent because the SrCl2 would be limiting the CO3.

2

It is assumed that strontium carbonate is insoluble. However, a very small amount of strontium carbonate is soluble in water

- What is the solubility of strontium carbonate?

By using the ICE method:

I: 0 (Sr+2) | 0 (CO32-)

C: +s (Sr+2) | +s (CO32-)

E: s (Sr+2) | s (CO32-)

The solubility product yielded 5.60e-10 so I made an equation where s X s = 5.60e-10. The solubility came out to be 2.37e-5 mol/L

- How will this affect the experimental percentage of carbonate in the unknown?

The experimental percentage will go down because more carbonate will pass through the filter paper due to being increasingly dissolved in the liquid.

3

In an attempt to complete the lab in less time, a group decided not to wash the precipitate with water. How will this affect the experimental percentage of carbonate in the unknown? Explain.

Since the precipitate is a solid, it could have traces of the solution around it. With this in mind, this could make the experimental percentage increase due to impurities generating more mass. The importance of washing the precipitate with water is to get a pure measurement of the precipitate. Without doing this could lead to error in experimental percentage.

Conclusion:

In the final analysis, we used alkali metal carbonate #5, and after numerous calculations dealing with experimental percentages and theoretical percentages, we narrowed the unknown to be sodium.