posted by Robert .
Our class did an expeiment of adding sodium carbonate and calcium chloride. The experiment only yielded 28% of the calculated yield. The class did the experiment as a group (there are only 4 students in our class) and the experiment was closely supervised by our teacher to ensure accuracy. Why was there so much descepency when everthing was done correctly?
Probably you will never know what but someone (or everyone) did something wrong. CaCO3 is soluble in acids; did the group use DI or distilled water? Did you filter? If so, are you sure the paper caught all of the ppt? Was this 28% the average of all four students or did everyone get 28%. How good were the reagents? Na2CO3 is not absolutely 100%; you never know how much of it is the decahydrate and how much is the monohydrate (or did you calculate the 28% yield based on thinking you used the decahydrate and you really did not? Finally, CaCl2 is a drying agent and absorbs water from the atmosphere. You can't weigh an amount of CaCl2 and know that's pure. It will always contain some water.