To celebrate the end of another successful semester of chemistry, one of the academics in the School of Chemistry will often make their famous 'buffer salad'. The ingredients to this salad are lettuce, cucumber, carrot, radish and the secret ingredient - a packet of salt and vinegar chips sprinkled throughout the salad. The salad is then finished off with a drizzle of 10.00 mL of vinegar as the dressing. When the salad is mixed, the vinegar dressing will dissolve the sodium acetate that is used to flavour the salt and vinegar chips. Since vinegar is itself a dilute solution of acetic acid, the dissolution of sodium acetate forms a buffer between the acetic acid and acetate ions.The concentration of acetic acid in vinegar has handily been found by some first-year chemistry students during their lab class as 0.95 M. The amount of sodium acetate present in a packet of salt and vinegar chips is quoted by the manufacturer as 0.45 g - you may assume that all of the sodium acetate will dissolve into the vinegar dressing. What is the pH of the famous 'buffer salad' dressing, to 2 decimal places?The pKa of acetic acid is 4.76The molar mass of sodium acetate is 82.0343 g/molUseful formula:
Question
To celebrate the end of another successful semester of chemistry, one of the academics in the School of Chemistry will often make their famous 'buffer salad'. The ingredients to this salad are lettuce, cucumber, carrot, radish and the secret ingredient - a packet of salt and vinegar chips sprinkled throughout the salad. The salad is then finished off with a drizzle of 10.00 mL of vinegar as the dressing. When the salad is mixed, the vinegar dressing will dissolve the sodium acetate that is used to flavour the salt and vinegar chips. Since vinegar is itself a dilute solution of acetic acid, the dissolution of sodium acetate forms a buffer between the acetic acid and acetate ions.The concentration of acetic acid in vinegar has handily been found by some first-year chemistry students during their lab class as 0.95 M. The amount of sodium acetate present in a packet of salt and vinegar chips is quoted by the manufacturer as 0.45 g - you may assume that all of the sodium acetate will dissolve into the vinegar dressing. What is the pH of the famous 'buffer salad' dressing, to 2 decimal places?The pKa of acetic acid is 4.76The molar mass of sodium acetate is 82.0343 g/molUseful formula:
Solution
The language of the text is English, so I will continue in English.
To find the pH of the buffer solution, we can use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
where:
- pKa is the acid dissociation constant of acetic acid (4.76)
- [A-] is the concentration of the acetate ion
- [HA] is the concentration of acetic acid
First, we need to find the moles of acetic acid and sodium acetate.
-
Calculate the moles of acetic acid in the vinegar: The concentration of acetic acid in the vinegar is 0.95 M, and the volume of vinegar is 10.00 mL or 0.01 L. Moles of acetic acid = Molarity * Volume = 0.95 M * 0.01 L = 0.0095 mol
-
Calculate the moles of sodium acetate in the chips: The mass of sodium acetate in the chips is 0.45 g, and the molar mass of sodium acetate is 82.0343 g/mol. Moles of sodium acetate = Mass / Molar mass = 0.45 g / 82.0343 g/mol = 0.00548 mol
Now, we can substitute these values into the Henderson-Hasselbalch equation:
pH = 4.76 + log(0.00548/0.0095) = 4.76 - 0.28 = 4.48
So, the pH of the famous 'buffer salad' dressing is 4.48, to 2 decimal places.
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