Physics Lab 2

Introduction:

The point of this experiment was to monitor the changes in pH of a titration of a weak polyprotic acid with a strong base to discover the Ka of the reaction. At the equivalence point it should show a dramatic change in pH as the solution goes from either acidic to basic or basic to acidic. To do this a pH meter was used. To calibrate a pH meter, first rinse the electrode in distilled water and submerse it in pH 7 buffer. Then press the calibrate button and wait until the pH icon stops flashing and says stable. Re-rinse the electrode in distilled water and submerse it in a pH 4 buffer and wait until the pH icon stops flashing to get a reading. Once this is done the Ph meter is calibrated. To use a pH meter place the probe in the sample liquid and wait until the reading becomes stable.

Reaction equations:

Ka=[HX][H3O]/[H2X]

H2X(aq) + NaOH(aq) = NaHX(aq) + H2O(l) pka1

NaHX(aq) + NaOH(aq) = Na2X(aq) + H2O(l)pka2

H2X(aq) + 2 NaOH = Na2X(aq) + 2 H2O(l)Overall reaction

Ka=[H3O]

pH= -log[H3O]

Procedure and observation:

The procedure of this experiment was to titrate to acids, citric acid and phosphoric acid, with NaOH and record the values of volume of NaOH and pH every 0.2 change in pH. This was done after recording your initial pH and completed once the pH reached 12. While doing this a table of data should be recorded. During the titration when the equivalence point was approaching and reached, the smallest amounts of NaOH changed the pH significantly. I also observed that the color didn’t change in the solution and the higher the pH the volume more NaOH was needed to increase the pH.

Data:

Citric Acid Titration | | | | Phosphoric Acid Titration | | | |

Volume of NaOH (mL) | pH | Volume of NaOH(mL) | pH | Volume of NaOH(mL) | pH | Volume of NaOH(mL) | pH |

0 | 2.47 | 57.5 | 7.78 | 0 | 2.19 | 35.9 | 7.61 |

4.5 | 2.67 | 59 | 7.98 | 8.13 | 2.39 | 37 | 7.82 |

7.3 | 2.87 | 59.05 | 8.4 | 11.7 | 2.65 | 37.8 | 8.03 |

10.5 | 3.07...