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# All odd slides - What is pH pH is defined as the negative...

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pH is defined as the negative logarithm of the hydrogen ion concentration pH = -log [H ] low pH values represent the highest [H + ] Henderson-Hasselbalch equation: the relationship between pH and the ratio of acid and conjugated base concentration . pH = Pk + log [A - ]/[HA] (conjugate base/conjugate acid) What is pH?

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To titrate several different samples and analyze titration behavior. To realize the importance of pH and Buffer - Henderson-Hasselbalch equation - The importance of pH - The importance of buffer To learn how to use a pH meter (optional). Titration Analysis
The Importance of pH in Biological Systems Biological reactions depend on strict regulation of hydrogen ion [H + ] concentration. Change in pH affect [H + ] concentration: a) affect rates of enzymatic reactions b) denature proteins – complete loss of activity

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The Importance of Buffer in Biological Systems Buffer Solution: 1) Weak conjugated acid-base solution containing both [A - ] and [HA]. Has ability to resist changes in pH when modest amount of acid or base are added. when a strong acid is added, the H + ions will be consumed by the conjugate base in the buffer, thereby removing most of the added H + from the solution: H + + A - HA When a strong base is added, the OH - ions will be neutralized by the acid in the buffer: OH - + HA A - + H 2 O 2) Effective range: 1 pH unit above and below its pKa. 3) Buffering capacity is determined by the concentration of buffer and its pKa.
Fruit juices are natural buffers. The tartness of pure fruit juices is largely due to a group of organic acids: 4 6 5 The fruit juice industry in the US alone is worth over \$12 billion per year

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4 samples: distilled water , 0.05 M acetic acid , apple juice , cranberry juice. First, acidify each sample with 1.0 M HCl (drop by drop) until pH is ~1.8 Titrate acidified solution with 2ml aliquots of NaOH, mix and measure pH. Repeat until pH is >11. Record all values in Table 1. Rinse pH meter w/ DI water after every sample. Magnetic Stirrer Procedure How to use a pH meter?
4 samples (50 ml each) distilled water, 0.05 M acetic acid, apple juice, cranberry juice acidify each sample with 1.0 M HCl (drop by drop) until pH is ~1.8 titrate with 2ml of NaOH, mix, measure and record repeat until pH is >11. Note: rinse pH meter w/ DI water after every sample waste disposal and clean-up Sample Procedure Outline

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Results and Analysis 1. Complete data table 1. 2. Make titration plot. 3. Answer question 2. Post-lab write-up: Observation & Results (3 pts) - Observation / Deviation: 1 pt - Table 1: 2 pts Analysis & Conclusion (6 pts) - Question 1 (plot): 3 pts - Question 2: 2 pts - Conclusion (explanation): 1 pt 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 2 4 6 8 10 12 14 16 18 ml of NaOH added pH H2O CH3COOH Apple Cranberry
Clean-up and Waste Disposal Clean-up: - Rinse and blot dry pH meter. Recap the pH meter. - Used Glass Pipets: openings point down in the pipet jar.

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