Describe how you would prepare 250 ml of 0.2M phosphate buffer, pH =12.5, given solid Na2HPO4.2H2O...

Question

Question

Describe how you would prepare 250 ml of 0.2M phosphate buffer, pH =12.5, given solid Na2HPO4.2H2O and Na3PO4.H2O. pKa= 4.75

science chemistry

Answer 1

Answer #1

The pKa value is given wrong. The actual value of pKa3 = 12.35

According to Henderson-Hasselbulch equation:

pH = pKa + Log[Na3PO4.H2O/Na2HPO4.2H2O]

12.5 = 12.35 + Log[Na3PO4.H2O/Na2HPO4.2H2O]

i.e. Log[Na3PO4.H2O/Na2HPO4.2H2O] = 0.15

i.e. [Na3PO4.H2O/Na2HPO4.2H2O] = 10^0.15 = 1.4125 ---- Equation 1

[Na2HPO4.2H2O + Na3PO4.H2O] = 250 mL * 0.2 mmol/mL = 50 mmol ---- Equation 2

From equations 1 and 2:

[Na2HPO4.2H2O] = 50/(1.4125+1) = 20.725 mmol

Now, [Na3PO4.H2O] = 50 - 20.725 = 29.275 mmol

The mass of Na2HPO4.2H2O required to prepare the given buffer = 20.725 mmol * 178 g/mol= 3.689 g

The mass of Na3PO4.H2O required to prepare the given buffer = 29.275 mmol * 182 g/mol = 5.328 g

Answer 2

Similar Homework Help Questions

menu TT 04.21120. pka=4.75 21. Describe how you would prepare 250 ml of 0.2M phosphate buffer,...

menu TT 04.21120. pka=4.75 21. Describe how you would prepare 250 ml of 0.2M phosphate buffer, pH -12.5, given solid Na2HPO4.2H20 and Na3PO4.H20. Ka=4.75
Describe how you would prepare one liter 0.1 M phosphate buffer, pH = 2.5, given 0.1...

Describe how you would prepare one liter 0.1 M phosphate buffer, pH = 2.5, given 0.1 M phosphoric acid and solid NaH2PO4.2H2O. pKa= 4.75
You need to prepare two buffer solutions for biochemistry lab. Describe how you would prepare the...

You need to prepare two buffer solutions for biochemistry lab. Describe how you would prepare the two buffers below: (1) 1.00L of 0.100 M acetate buffer at pH 4.00. pKa acetate: 4.75 (2) 1.00 L of 0.100 M sodium phosphate buffer at pH 7.00 pKa sodium phosphate: 7.21

How you would prepare a solution of 250.0 mL of a 0.150M phosphate buffer at ph=7....

How you would prepare a solution of 250.0 mL of a 0.150M phosphate buffer at ph=7. (phosphoric acid pka1=2.12, pka2=7.21, pka3=12.32). What would the pH of the buffer be if 5.00mL of 1.10M HCL was added to 100mL sample of the prepared buffer.
1) How would you make 300 ml of a 0.1 M sodium phosphate buffer, pH 7.0...

1) How would you make 300 ml of a 0.1 M sodium phosphate buffer, pH 7.0 (pKa = 7.2) phosphate dibasic (the conjugate base). 2) What are the concentrations of acetate and acetic acid in a 0.2 M acetate buffer pH 5.3? The pKa for acetic acid is 4.76. 3)You have 100 ml of 0.1 M acetate buffer pH 5.2 (pKa 4.76). You add 10 ml of 0.1 M NaOH. Calculate the resulting change in pH and the buffering capacity...
Calculate how to prepare 200 mL of a 0.1 M sodium phosphate buffer at pH 6.8...

Calculate how to prepare 200 mL of a 0.1 M sodium phosphate buffer at pH 6.8 by combining two separate solutions of 0.1 M NaH2PO4.2H2O and Na2HPO4)? Molecular weight NaH2PO4.2H2O = 156 g/mol; molecular weight Na2HPO4: 141.96 g/mol. Use 6.86 as the pKa and prepare 250 mL of the separate solutions.

a) What are the concentrations of Na2HPO4 and NaH2PO4 in a 0.30 M phosphate buffer solution...

a) What are the concentrations of Na2HPO4 and NaH2PO4 in a 0.30 M phosphate buffer solution pH 7.0? Use pKa 6.82 b) Describe how you would prepare 250 mL of the buffer in part (a) given that you have available to you a 1.0 M stock solution of NaH2PO4 and solid Na2HPO4(FW 141.96 g/mol). Provide your answer in milliliters of NaH2PO4 and grams of Na2HPO4. c) Suppose you use 100 ml of this buffer in an experiment and 0.003 mol...
Describe how would you prepare 500.0 mL of buffer with pH = 9.08 and [HA] +...

Describe how would you prepare 500.0 mL of buffer with pH = 9.08 and [HA] + [A−] = 0.10 M using the following reagents available to you in the stock room and any appropriate glassware. Available: NH4Cl (F.W. = 53.5) Ka = 5.5×10−10 pKa = 9.26 6.00M HC2H3O2 Ka = 1.8×10−5 pKa = 4.74 NaH2PO4•H2O (F.W. = 137.99) Ka = 7.4×10−8 pKa = 7.13 3.00M NaOH Deionized H2O 1) Pick the correct weak acid. 2) Solve the Henderson-Hasselbalch equation for...
In order to prepare 100 mL of a 0.50 M sodium phosphate buffer, pH 7.9, how...

In order to prepare 100 mL of a 0.50 M sodium phosphate buffer, pH 7.9, how many grams of sodium phosphate monobasic must you add to your solution? Use MW = 137.99 g/mol for sodium phosphate monobasic and pKa = 7.2 for sodium phosphate

You need to prepare 100.0mL of a 50.0mM phosphate buffer with a pH of 7.00. The...

You need to prepare 100.0mL of a 50.0mM phosphate buffer with a pH of 7.00. The pKa for this form of phosphate is 6.82. Calculate the weight of NaH2PO4*H2O and volume of 1.00M NaOH that you will require.