Post-Lab Question (to be included in the discussion section of your lab report)
ID: 1033650 • Letter: P
Question
Post-Lab Question (to be included in the discussion section of your lab report) Determining the Concentration of an HCl solution Consider each of the following potential sources of error. Explain how your calculated molarity of HCI would be affected and why. Be specific. Would the molarity be larger, smaller, or unaffected? Explain. 1. A little distilled water was in the Erlenmeyer flask before you added the HCl to it. While you were titrating, some of the NaoH dripped onto the table instead of into the Erlenmeyer flask. While pipetting the HCl solution, several drops of HCl drip out of your pipet onto the bench top. You added several drops of phenolphthalein instead of just 2 or 3. a. b. c. d.Explanation / Answer
To calculate the molarity of HCl we titrate with standard solution of NaOH
Molarity of standard solution of NaOH is calculated by formula
Molarity = weight of NaOH*1000/molar mass of NaOH*volume of solution
then Molarity of HCl is calculated by formula
M1V1(NaOH) = M2V2(HCl)
a). when a small amount of distilled water was already there in Erlenmeyer flask before adding HCl to it
Molarity of HCl is decreased in this case this is because M2(HCl) = M1V1(NaOH)/volume of HCl solution and volume of HCl increase because small amount of water mix to it. So as volume of HCl increase molarity of HCl decrease.
b) while titrating some drops of NaOH falls on table instead of flask
in this case also Molarity of HCl decrease because as some drops falls out so volume of NaOH solution added decreased and as volume of NaOH solution decrease Molarity of HCl decreased
M2(HCl) = M1V1(NaOH)/volume of HCl solution and V1is volume of NaOH added.
c). while pipetting out HCl some drops of HCl drip out on the bench
in this case Molarity of HCl increased because total volume of HCl taken in flask is decreased as some drops are fell down outside flask. So as volume of HCl taken decreased Molarity of HCl increased beacuse
M2(HCl) = M1V1(NaOH)/volume of HCl solution
d). you added serveral drops of phenolphthalein instead of just 2 or 3
in this case no effect on Molarity of HCl because phenolphthalein is just an indicator it does not effect the Molarity of HCl.