The purpose of this lab is as follows: To use mole ratios to predict the amount of precipitate formed, to use mole ratios to study the effect of reactant molarity on the yield of product, to use mole ratios to study limiting and excess reactants, and to design an experiment which achieves the above objectives.
The exact reacting ratio has to come into play when the two solutions are mixed. The molarity of the solution given must calculated before the experimentation process begins. One of the reactants will stay the same and the other one will change. This reactant will change in volume, thus being the independent variable. There will be a precipitate forming from the reaction of the two reactants. The molarity of the changing reactant is to be calculated. To do this, the concept of the exact reacting ratio should be comprehended. When two solutions are mixed and the ratio of their moles is perfect, this will be the exact reacting ratio. But when the ratio is not perfect (which in most cases it will not be) then one of the chemicals will be left over. It will not be fully used. The reactant that is fully used is called the limiting reacting because it is limiting the other reactant from fully reacting. The reactant that is not fully used up is the excess reactant. This one is left over. These concepts could be more easily grasped and understood through an example. How many hamburgers can you make with 8 buns and 5 pieces of meat? Only 5. In this case, the buns are the excess reactant because they will not be used up; the meat is the limiting reactant.
[...] Observations K2C2O4*H2O appeared to be a clear and transparent solution. SrCl2 was a ball-like salt. They were white and were very hard to dissolve. Stirring rods were used to crush the balls and even still it was difficult to dissolve it. We shook the flask very violently for a relatively long period of time and finally it dissolved. When the K2C2O4*H2O and SrCl2*6H2O were reacted, they were at first clear, retaining their natural color. After a couple of minutes it began to solidify. [...]
[...] This and the mole ratio can be used with the two reactants to get the molarity of the solution. If there are two reactants A and B then this is how the number moles of reactant A are calculated: Before the reaction takes place, it is necessary that each person make their solutions. One must know how much K2C2O4 they should use. The calculations for this are as follows: After the reaction takes place, there is supposed to be something that has precipitated. [...]
[...] No, the mass didn't disappear; the quadruple beam balances are simply not reliable and have been abused too much. Even if we did have good balances, nothing is perfect. There is always room for error and it is inevitable. The human eye is not perfect so when we measured out our solutions, we could have been a little off on our measurements. Some of the SrCl2 probably did not fully react. In result this will give us inaccurate results in the end. [...]
[...] After precipitate is massed, the percent yield of the product and percent error will be calculated. If the percent error is positive, this means that the result was higher than was expected. Do not think your calculations are wrong if the percent error is negative. This happens because the result was simply lower than one had expected. When the graphing begins, it is imperative to plot the theoretical and experimental results on the graph. The molarity of the solution k2C2O4*H2O will be the independent variable on the graph and the mass of the precipitate will be the dependant variable. [...]
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