UNKNOWN ACID AND BASE TITRATION
The purpose of this lab is to determine the concentration of a hydrochloric acid solution using acid-base titration. When the base was added to the acid, the indicator in the acid turned the solution pink when the end point of titration was reached.
Part I: Measuring pH
Step 1: Measure pH of 0.1 M hydrochloric acid
1) Select Equipment from the toolbar
2) Select a 100 mL beaker
3) Add 50 mL of 0.1 M hydrochloric acid to the beaker by right clicking on the beaker and selecting Chemicals. Select 50 mL of 0.1 M hydrochloric acid and then click OK.
4) To measure the pH of the solution, right click on the beaker and select pH Meter. The number in the box displays the recorded pH. Then record the pH.
Step 2: Measure the pH of 0.1 M sodium hydroxide.
1) Repeat the steps above for 50 mL of 0.1 M sodium hydroxide and record the pH.
Part II: Acid-Base Titration
Step 1: Add 35 mL of Unknown Acid A to 100 mL beaker. (The acid is HCl.)
1) Click on Chemicals from the toolbar and select All Chemicals from the dropdown menu. Then select Unknown Acid A.
2) Change the volume to 35 mL. (Be sure to check that on the lower part of the window, you have indicated that the unknown acid is to be added to a new 100 mL beaker) Then click OK.
Step 2: Add two drops of phenolphthalein indicator to the beaker.
1) Right-click on the beaker and select Indicators. Select Phenolphthalein and add 2 drops,
Step 3: Obtain a 50 mL buret, and fill it with 50 mL of 0.1 M NaOH solution.
1) Right click on the working area, other than the beaker. Select a 50 mL buret and right click on the buret and select Chemicals.
2) Add 50 mL of 0.1 M sodium hydroxide to the buret. Position the buret above the beaker.
Step 4: Titrate Unknown Acid A (HCl) with NaOH, until the end point. Record the volume of NaOH used.
1) Right click on the working area, other than the beaker. Then right click on the beaker and select pH meter. Record the starting pH.
2) Right click on the buret and select Titration Dialog box. (Before starting, right click on the beaker and select Collect Titration Data. Also select View Titration Data from the Procedures dropdown menu.)
3) To begin the titration, open the stopcock of the buret using the command in the titration dialog box.
4) To titrate the acid with the NaOH, be sure to add the NaOH slowly to the acid solution. This only opens the stopcock by a small amount. From the titration dialog box, observe the beginning volume of the NaOH in the buret. To stop the addition of the NaOH, click Close on the stopcock command.
5) Record the volume of NaOH added and the pH of the solution. Near the endpoint of the titration, the pH can change rapidly with very little addition of NaOH. Click Close as soon as the pH of the solution turns pink. Record the volume and the pH.
Observations and Results
Part I: Solution pH 0.1 M HCl