Okay, So here is my dilemma: (This is a significant figure question - So, all gi

Question

Okay,

So here is my dilemma:

(This is a significant figure question - So, all given numeric values are noted as given.)

I did a lab in Chemistry called Oxidation-Reduction Titration (2 experiments in 1, and 3 titration per experiment).   

Experiment 1 - Trial 1:

First, a known concentration on oxalic acid (COOH)2 (0.1 M - Given by instructor) was used as the titrate.

10.00 mL of oxalic acid was put into a Erlenmeyer flask.

An unknown concentration of potassium permanganate, KMnO4, was put in a buret and added to the oxalic acid (a small amount at a time until titrated - mixture stayed pink for at least 30 seconds).

When calculating the concentration of the potassium permanganate, I used the stoichiometery values of both substances, the concentration of oxalic acid and volumes of both.

Example:

(0.1000L of oxalic acid used)(0.1 mol oxalic acid/ 1 L)(2 mol KMnO4/5 mol (COOH)2)= The mols of KMnO4 used in titration = 0.0004 mols KMnO4

The total volume of KMnO4 used was 20.50 mL.

Total number of KMnO4 mols used was divided by total volume of KMnO4 used. (0.0004/0.02050 L) = 0.01951 M KMnO4

This was repeat 2 more times. My question is how many significant figures should I report for my concentration of KMnO4 ? The reason why I am confused is because I need to give the average as my answer. Also, I need to calculate the standard deviation which equals 0.00011317. The example is the lab manual says, if you concentration results are 0.0234 M, 0.0232 M, and 0.0228 M, the standard deviation would be =0.0003.

Am I suppose to use the standard deviation to know the number of significant numbers to use? I am not sure what 0.0003 means and what it means as far as the number of significant numbers to use.

When I am finding my average, do I only use one sig fig? The book used 3 sig figs to calculate the standard deviation example.

The picture attached is my rough copy of what I have filled in so far; however, I am not confident about the number of sig figs I have used. (I added 2 sig figs to the standard deviation value because the answer had a "1" as the first "natural" number. I believe in this case, a second figure is added regardless if only one sig fig is only required.

Can you help me figure out the sig figs I should be including for each line in Experiment 1, Trial 1?

Thanks!

Chem 1212 Lab Manual Oxidation-Reduction Titration REPORT SHEET Section Date Name Instructor Partner's Name Show all the steps for determining the overall net nic equation by the method of half reactions for the redox reaction of permanganate with oxalic acid. The two unbalanced half reactions are provided. (5 pts) CO (COOH) meles Mno u reads witn 5 moves (Coo CExcept where otherwise noted, 2 pts, for all blanks.) Molarity of oxalic Acid O M Trial 3 Tria 3 Trial 1 orn Volume of Oxalic Acid back Initial Buret Volume of KMno4 o mL. Final Buret Volume of KMno4 20,so mi do. Com mu 21. to me. Volume of KMno4 added Calculated Molarity of KMno4 Average Calculated Molarity OrO2Mes pts) Standard Deviation g oooh!tu of KMnO4 Unknown Code for Oxalic Acid (0 pt. Trial 3 Trial 2 Trial 1 Volume of Oxalic Acid of Unknown Concentration Initial Buret volume of KMno4 Final Buret Volume of KMno4 Volume of KMno4 added Calculated Molarity of Oxalic Acid 72

Explanation / Answer

Calculated Molarity of KMno4 : Calculations are preferred in 4 significant figures

A1 =0.0195 M

A2= 0.0193 M

A3= 0.0148 M

A =Average = Sum/3 = 0.0179

Standard deviation calcualtion:

= Sqr root[{ (sqr (A-A1) + Sqr (A-A2) +sqr (A-A3) } / 3 ]

= 0.0022

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