SADAF pH at the UN - Sadaf Ayaz Chem 106 pH at the UN...

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Sadaf Ayaz Chem 106 pH at the UN Partners: Natalia and Gabby TA: Edmund Tam
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Part 1 Observations: 0.1M HCl: clear liquid 0.1M H 2 SO 4 : clear liquid 0.1M H 3 PO 4 : clear liquid 0.1M CH 3 COOH (acetic acid): clear liquid 0.1M CH 3 COOH/0.2M KCH 3 COO (acetic acid/potassium acetate buffer): clear liquid 0.1M NaOH: clear liquid Bromothymol blue indicator: dark blue liquid Universal indicator solution: dark red liquid Sodium Sulfate (Na 2 SO 4 ): white solid 0.1M Nitric Acid: clear liquid 1.0M Sodium acetate (NaC 2 H 3 O 2 ): white solid 0.1M Ammonia (NH 3 ): clear liquid 0.5M Sodium citrate: white powder Ammonium Chloride: white solid Potassium Sulfate: white solid Potassium dihydrogen phosphate: white solid Potassium hydrogen phosphate: white solid Part 2 Observations: Universal Indicator: really dark green 0.1M Sodium Hydroxide: clear bubbly liquid 0.1M HCl: clear liquid 0.1M H 2 SO 4 : clear liquid 0.1M H 3 PO 4 : clear liquid 0.1M CH 3 COOH: clear liquid 0.1M CH 3 COOH/0.2M KCH 3 COO: clear liquid
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Part 3 Observations: Bromothymol blue: dark blue liquid 0.1M NaOH: clear liquid 0.1M HCl: clear liquid 0.1M acetic acid: clear liquid 0.1M acetic acid/0.2M potassium acetate: clear liquid Part 4 Observations: 0.1 M Acetic Acid: clear water-like 0.1 M Sodium Acetate: clear water-like 0.1 M HCl: clear water-like 0.1 M NaOH: clear water-like Titrating 0.1 M NaOH in Buffer As the amount of the NaOH chemical increased by the mL the pH went from a pH of around 5 (a greenish color) to a pH of around 11 (a color of blue) in both trials. Titrating 0.1 M HCL in Buffe r As the amount of the HCl chemical increased by the mL the pH went from a pH of around 5 (a greenish color) to a pH of around 0.8 (a color of blue) in both trials. Part 4 Design of Experiment: 1. Make a buffer with a pH of 5. The volume of the buffer should be 50 mL 2. For this experiment we will make 50mL of a buffer with the pH of 5 and test if it works. We make a buffer by adding acetic acid (weak acid) and sodium acetate (weak base). To find the ratio of the acid to base we use the Henderson- Hasselback equation 3. By setting the pH to 5 and using the the pka constant for aceitic acid; 1.8 x 10-5 4. We then separate 10mL of the 50 mL of the buffer and added titrated the acid then the base. We then test the pH at each mL titrated.
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5. Creating the buffer: Add 32.14 mL of Sodium Acetate with 17.86 mL of Acetic Acid. 6. Titrate 0.1 M HCl to determine whether or not the buffer buffers an acid. 7. Re-do step 5 8. Titrate 0.1 M NaOH to determine whether or not the buffer buffers a base Calculations: pH = pKa + log(base/acid) Ka = 1.8x10^-5 pKa = -log(1.8x10^-5) = 4.74 5 = 4.74 + log(Base/Acid) log(Base/Acid) = 0.26 10^0.26 = 10^log(Base/Acid) 1.8/1 = Base/Acid 1.8/2.8 = xmL/50mL X = 32.14mL of base 50 - 32.14 = 17.86mL of ac id Post Lab Questions: PART THREE: Case 1 1. Examine your graphs (1a and 2a). Discuss why 1a is a more useful plot. Graph 1a, which represents the experimental pH vs the volume of base added is a more useful graph then graph 2a which portrays the concentration of acid vs the volume of base added because it allows us to closely examine the relationship between HCl and NaOH having smaller
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changes in the y-axis, thus forming a titration curve. The titration curve allows us to see the
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