Direct titration of Tums (CaCO3), with HCl results in a fading endpoint requiring several additions of HCl before a permanent blue to yellow color change is observed.

1. Write the reaction that is occurring in this titration.

2. What is the reason for the fading endpoint in this direct titration?

3. How is this problem eliminated in the back titration procedure?

4.A graduated cylinder can be read to the nearest 1 ml. What percent error does this represent in a total volume of 25 ml?

5.A buret can be read to the nearest 0.02 ml. What percent error does this represent in a total volume of 25.00 ml?

6.How much larger (ratio) is the measurement error in using a graduated cylinder compared to using a buret to measure 25 ml of HCl?

6.Baking soda, NaHCO3, can be used to neutralize acid spills, resulting in a nearly neutral solution. How many grams of NaHCO3 would be required to neutralize a spill of 50. ml
of 1.0 M HCl? MWt of NaHCO3 = 84

7. What salt is contained in solution after the acid is neutralized?