2. Add 25 Ml Hcl (Of Unknown Concentration) to the Flask

2. Add 25 mL HCl (of unknown concentration) to the flask.

3. Add 2 drops of phenolphthalein, an indicator, to the flask.

4.Take a burette from the Glassware shelf and place it on the workbench.

5. Fill the burette with 50 mL of 0.5M NaOH solution. Record this initial volume.

6. Drag the flask to the lower half of the burette such that the burette can deliver NaOH to the flask. Make sure the burette and the flask are connected.

7. Open the Data window and click on the flask. Click the pushpin icon in the Data window to lock its display to the flask.

8. Take a pH meter from the Tools shelf and set it on the flask. Record the initial pH of the solution.

9. Open the Properties window and click on the burette. Enter "1" in the amount window to add NaOH to the flask in 1 mL increments. One mL of NaOH will be delivered to the flask each time the stopcock button is clicked.

10. Set up a data table on a piece of paper with the following column headings:

mL of base (burette reading)

pH

moles of NaOH

11. Click the stopcock button on the Properties window to deliver 1 mL of NaOH to the flask. Continue to add NaOH in 1 mL increments. Record the mL of base (burette reading), the pH of the solution in the flask, and the moles of NaOH in the flask for each mL of base added. Note that the initial mL of base is 50 mL, which is equal to zero mL of base added to the flask.

12. The solution in the flask will change in color from clear to pink due to the phenolphthalein indicator when the endpoint is either reached or crossed. Mark the point in the data table at which the color change occurs.

13. Add 5 more 1 mL increments of NaOH to the flask recording the mL of base, the pH, and the moles of NaOH at each increment.

14. Detach the pH meter and drag the burette and flask to the recycling chute.

15. Take a new flask from the Glassware shelf and place it on the workbench.

16. Add 25 mL of HCl and 2 drops of phenolphthalein to the flask.

17. Set a new burette on the workbench and fill it with 50 mL of NaOH.

18. Place the flask under the burette and attach the pH meter.

19. Based on the results of the previous titration, you may initially add a relatively large amount of NaOH solution all at once to the flask to get to 1 mL BEFORE the endpoint. For example, if 20 mL of NaOH caused a color change in your first titration, you know experimentally that you can add 19 mL of NaOH to the second titration without causing a color change. You can enter 19 in the Properties window and click the stopcock button to deliver 19 mL of NaOH to the flask at once.

20. AFTER the initial delivery of NaOH to the flask, change the amount of NaOH to be delivered to 1 in the Properties window. For this titration, use the DROP-WISE button to deliver very small (0.05 mL) of NaOH per click of the drop-wise button. In this way, you are measuring the endpoint of titration more precisely. Record the mL of base (burette reading), the pH, and the moles of NaOH in the flask with each click of the drop-wise button until the endpoint is reached. Mark this endpoint on your data sheet. Add 5 more drop-wise increments of NaOH noting the mL of base, pH, and moles of NaOH.

1. i)At what point did your solution turn pink?

ii)What is the pH at the equivalence point?

iii)What is the equivalence point volume of NaOH?

iv)Calculate the molarity of the HCl from the volumes of acid and base at the equivalence point and the molarity of the NaOH. (Use the equation given in the Background section.)

v)

When titrating a monoprotic acid, such as HCl, with sodium hydroxide (NaOH), the molar ratio for the reaction is 1:1 - that is, one mole of NaOH will neutralize one mole of HCl - and all of the following are true at the equivalence point:

(a) Moles of acid in flask = moles of base added from the buret

(b) (molarity of acid) x (volume of acid) = (molarity of the base) x (volume of added base)

Equation (b) takes the familiar form M1*V1 = M2*V2, from which the molarity of the acid, M2, is determined.

vi)Compare the value of molarity determined individually. Are all these values same? Why, or why not?

pH changed color to pink on first run at a pH of 12.39. The moles NaCl stayed at 0.015000from there on out

On the second run with the initialadministration of 15 ml and then the reduced amounts administeredthe pH changed at 11.79 NaCl moles remained the same.