Enable text based alternatives for graph display and drawing entry

Click here to erase all data entry on this page

Acid-Base Titration: Unknown HCl

 

Titrations provide a method of quantitatively measuring the concentration of an unknown solution. In an acid-base titration, this is done by delivering a titrant of known concentration into an analyte of known volume.

In this video we'll show you how to use pipets:

In this video we'll show you how to operate the buret:

In this assignment, you will titrate a 0.2564 M solution of NaOH into 25 mL of an unknown concentration of HCl and calculate the concentration of the HCl solution. 

 

  1. To start this activity, click this link for Acid-Base Titration: Unknown HCl. The lab will open in the Titrations laboratory. You can follow along with the instructions below in the Procedures tab in the lab.
  1. The buret is filled with 0.2564 M NaOH. You need to measure out 25.00 mL of HCl with unknown concentration. Pour some HCl into the beaker under the pipet- you'll need the beaker about 1/3-1/2 full (so there is enough to fill the pipet). Click the blue pipet bulb to pull the solution up into the pipet. Move that beaker into the red disposal bin and then move the empty beaker to the right of the stirplate under the pipet. Click the blue bulb to release the 25 mL into the new beaker. Drag the beaker to the stirplate. Click on the Bro G indicator bottle and drag the dropper to the beaker to add the indicator bromocresol green. Or you can use whatever indicator you know will change color in the appropriate range for this titration.
  2. The pH meter is turned on and has been calibrated. Drag it to the beaker and release it in the beaker.
  3. Click the Save Data button in the buret section of the Live Data tab so the titration data will be saved. The horizontal position of the orange handle is off for the stopcock. Open the stopcock by pulling down on the orange handle. The vertical position delivers solution the fastest with three intermediate rates in between. Turn the stopcock to one of the fastest positions. Observe the titration curve. When the blue line in the graph window (the pH curve) begins to turn up, double-click the stopcock to turn it off. Move the stopcock down one position to add volume drop by drop.

There are two methods for determining the volume at the equivalence point: (1) Stop the titration (close the stopcock) when a color change occurs, and then click the red Stop Saving button in Live Data. Open the Lab Book tab in the tray and scroll down to the last line in the data table and record the volume at the equivalence point. OR (2) Add drops slowly through the equivalence point until the pH reaches approximately 12. Click the Saving Data button. In the Lab Book tab, click the Copy Data button at the top right of the data table to copy the data and then you can paste the data into a spreadsheet program. Plot the first derivative of pH vs. volume. The peak will indicate the volume of the equivalence point since this is where the pH is changing the most rapidly as the volume changes.

 

5.         What volume of 0.2564 M NaOH was required by the titration to reach the equivalence point?

mL

  1. Calculate the molarity of the HCl using 25.00 mL of HCl solution and the volume of the 0.2564 M NaOH from your titration. 

Your calculated molarity: M HCl

Open the Unknowns tab in the tray, expand the Assigned Unknowns menu and enter your calculated molarity. Click Submit. Report the actual result that the program tells you you had here. That is also recorded in your LabBook.

Actual result: M HCl