We win use these reagents in several experiments throughout me semester. Each gr

Question

We win use these reagents in several experiments throughout me semester. Each group will prepare one solution. Work together to prepare these solutions. Need 500 mL of 0.1 M Glycine Buffer, pH 10.0 - 2 Groups prepare this What is the formula weight of Glycine? How many grams of Glycine do you need? How many ml of water will you dissolve the Glycine in? {What is the expected pH of the original solution? Will you need to add HCI or NaOH to the original solution to adjust the pH to 10.0? (1) How much HCI/NaOH do you expect to need to add? What concentration of HCI/NaOH? (5) How much HCI/NaOH did you actually add to achieve pH 10.0? (1)

Explanation / Answer

1. To prepare 500 ml of 0.1 M glycine buffer with pH 10

For buffer use Hendersen-Hasselbalck equation

pH = pKa + log(base/acid)

10 = 9.60 + log(glycine/glycine-HCl)

[glycine] = 2.51[glycine-HCl]

[glycine] + [glycine-HCl] = 0.1 M x 0.5 L = 0.05 mol

2.51[glycine-HCl] + [glycine-HCl] = 0.05 mol

[glycine-HCl] = 0.05/3.51 = 0.014 mol

[glycine] = 0.05 - 0.014 = 0.036 mol

glycine = 0.036 mol x 75.06 g/mol = 2.70 g

[NaOH] to be added = 0.036 mol/0.5 L = 0.072 M

So,

a. formula weight of glycine = 75.066 g/mol

b. grams of glycine required = 0.05 mol x 75.066 g/mol = 3.75 g

c. volume of water required = 500 ml

d. pH of solution = 1/2(9.60 + 2.34) = 5.97

e. We would add NaOH to the original solution to get pH 10

f. Expected NaOH molarity needed = 0.072 M

g. amount of NaOH to be added = 0.01 L

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