Answer the following questions at the end of your lab report

Answer the following questions at the end of your lab report: Tell whether each of the situations described below would cause the experimental value for the concentration of iron(II) in this experiment to be greater than, less than, or unchanged from the theoretical value. Explain your reasoning in each case. a. The student uses 95. mL of 1.0 M HCl instead of 90. mL of 1.0 M HCl. b. The student misreads the buret at the end point as 24.83 mL when it should have been 23.17 mL. c. The student used 25 drops rather than 5 drops of barium diphenylaminesulfonate indicator. d. The student failed to transfer all of the potassium dichromate from the weighing paper into the volumetric flask. e. The student\'s unknown solution already had been partially oxidized to Fe3+

Solution

a)

concentration will be using more H+ ions

which react with more Fe+2

then

molarity will be higher since it is directly related.

b)

V is larger than an actual value

so

total mol of HCl used is higher, then

molarity of Fe+2 will be higher.

c)

if the indicator is used in excess it takes few more drops of potassium dichromate after the reaction is completed. to show the color change in K2Cr2O7 is used be excess then the required amount, so the concentration of Fe+2 ions will be higher than the actual value during calculation.

d)

if the student fails to transfer tK2Cr2O7 completely to the volumetric flask then the concentration of K2Cr2O7 is less than the calculated value. so excess amount of the K2Cr2O7 solution is needed to reach the endpoint, therefore, the concentration of Fe+2 ions will be higher than the original value.

e)

if the unknown solution has already been partially oxidized to Fe+3 then he will need less amount of potassium dichromate solution to reach the endpoint as most of the Fe+2 ions have already be oxidized to Fe+3 so he will get less concentration of Fe+2 than the actual concentration of an unkown solution.