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11 Dec 2019

You need to prepare 5 liters of 2 M sodium phospate buffer, pH 7.4. You have stocks of 1 M monobasic sodium phosphate (NaH2PO4) and 1 M dibasic sodium phosphste (Na2HPO4). How much of each stock solution should be combined to make this buffer? The pKa of monobasic sodium phosphate is 6.82.

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Trinidad Tremblay
Trinidad TremblayLv2
13 Dec 2019

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Related questions

You work in a medical research lab with a biochemist who asks you to make a 1.00 L phosphate buffer stock solution with pH = 7.4. The total phosphorus concentration is to be 0.250 M.

In the storeroom, there are the following reagents:  a 2.00 M phosphoric acid stock solution,  solid sodium dihydrogen phosphate, (MM 120 g/mol)  solid sodium hydrogen phosphate, (MM 142 g/mol)  solid, sodium phosphate, (MM 164 g/mol)  a 1.00 M HCl(aq) stock solution,  a 1.00 M NaOH(aq) stock solution, and  deionized water.

a) To make an optimum buffer, it is important that the pKa of the acid part is close to the target pH of the buffer. Which phosphate species has a pKa value closest to pH = 7.4?

Sodium Phosphate buffer has 3 ionizable groups, with pKa's of 2.15, 7.20 and 12.45. A 1.00 M solution of this buffer (200 mL) is found to have a pH of 7.50 A biochemist adds 30.0 mL of 1.00 M HCL to this buffer.


(a) How many moles of Na2HPO4 and NaH2PO4 are present before the addition of HCl?


(b) What is the resultant pH after the addition of HCL?


(C) How many total milliliters of 0.350 M NaOH can you add to the final solution in Question 8b and still maintain as a good phosphate buffer (i.e. within 1 pH unit of pKa).

You work in a medical research lab with a biochemist who asks you to make a 1.00 L phosphate buffer stock solution with pH = 7.4. The total phosphorus concentration is to be 0.250 M. In the storeroom, there are the following reagents: (1) a 3.00 M phosphoric acid stock solution, (2) solid sodium dihydrogen phosphate, (3) solid sodium monohydrogen phosphate, (4) solid, sodium phosphate, (5) a 3.00 M HCl(aq) stock solution, (6) a 3.00 M NaOH(aq) stock solution, and (7) deionized water.

(i) (2 pts) To make an optimum buffer, it is important that the pKa of the acid part is close to the target pH of the buffer. Which phosphate species has a pKa value closest to pH = 7.4?

(ii) (4 pts) Choose this phosphate species (in i) as the only phosphorus component. What amounts of this substance and any other reagents (grams of solid(s); mL of any solution(s) and water) would you need to make the buffer with pH = 7.4?

(iii)(4 pts) Choose this phosphate species (in i) and either its conjugate acid or base as the only two phosphorus components. What amounts of this substance, its conjugate acid or base, and water (grams of solid(s); mL of any solution(s) and water) would you need to make the buffer with pH = 7.4?

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