Identification of an Unknown Salt Data, Unknown #4
This is data that is very much like what you would have gotten if you were doing the actual experiment. It is not perfect. This particular experiment is tricky because one indicator is supposed to be good enough for four different salts that in reality, have four different endpoints. Don’t be alarmed at your percent error. You should be able to figure out the identity of your unknown.
All the salts are white, crystalline powders.
Titrant used was 0.1001 M HCl.
Since they are all different molar masses, we need to do a small initial titration to determine the correct amount to use for the following three titrations.
Initial mass: .104 g salt
Titration used: 11.16 mL HCl, approximately 11 mL
To scale this up between 25 mL and 35 mL, we decided that since 11 X 2 is 22, and 11 X 3 is 33, we should make the sample sizes 2.5 times larger.
Titration 1: 0.2611 g salt, used 31.15 mL HCl
Titration 2: 0.2452 g salt, used 30.74 mL HCl
Note: Many tiny bubbles are seen in all the titrations.
Before doing titration 3, you must use the data from 1 and 2 to figure out how to tell where the halfway point is going to be for titration 3. We will stop at the halfway point and measure the pH.
There are two ways to do this. We can calculate the molar mass (which you must do for the report anyway), take the average, and then figure out how much HCl the third sample should use based on that molar mass and the mass of the sample. The second way is to calculate the number of milliliters per gram and then average that. Use average mL/g to calculate where the endpoint should be for the third sample. We will stop halfway to the endpoint.
Use one of these methods to calculate where the halfway point should be for titration 3 based on the mass of the sample below.
Titration 3: 0.2677 g salt