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?

Answer 1

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.