Preparation of pH buffer solutions

The different names for phosphate salts. Standardization buffers pH 4 and pH 7. Ph range of some buffer systems. Making up buffer solutions by adding an adjuster solution (acid or base) to a known volume and concentration of a primary salt solution. Potassium hydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, potassium hydrogen phthalate, sodium acetate,sodium tetraborate, tris aminomethane.

Phosphates

Phosphate salts are known by several names and the correct phosphate must be used to prepare buffer solutions. One phosphate cannot be substituted for another phosphate. Check formula of salt to be certain.

Formula	Name of salt	Other names
KH2PO4	potassium dihydrogen phosphate	potassium dihydrogen orthophosphate monobasic potassium phosphate monopotassium phosphate acid potassium phosphate potassium biphosphate
K2HPO4	potassium hydrogen phosphate	dipotassium hydrogen orthophosphate dipotassium hydrogen phosphate dibasic potassium phosphate dipotassium phosphate
K3PO4	potassium phosphate	tribasic potassium phosphate tripotassium phosphate

Standardization buffers For pH=7.00 : Add 29.1 ml of 0.1 molar NaOH to 50 ml 0.1 molar potassium dihydrogen phosphate. Alternatively : Dissolve 1.20g of sodium dihydrogen phosphate and 0.885g of disidium hydrogen phosphate in 1 liter volume distilled water. For pH= 4.00 : Add 0.1 ml of 0.1 molar NaOH to 50 ml of 0.1 molar potassium hydrogen phthalate . Alternatively : Dissolve 8.954g of disodium hydrogen phosphste.12 H2O and 3.4023g of potassium dihydrogen phosphate in 1 liter volume distilled water.

Range of common buffer systems ¹

Buffering system	Useful buffering pH range @ 25°C
Hydrochloric acid/ Potassium chloride	1.0 - 2.2
Glycine/ Hydrochloric acid	2.2 - 3.6
Potassium hydrogen phthalate/ Hydrochloric acid	2.2 - 4.0
Citric acid/ Sodium citrate	3.0 - 6.2
Sodium acetate/ Acetic acid	3.7 - 5.6
Potassium hydrogen phtaalate/ Sodium hydroxide	4.1 - 5.9
Disodium hydrogen phthalate / Sodium dihydrogen orthophospate	5.8 - 8.0
Dipotassium hydrogen phthalate / Potassium dihydrogen orthophospate	5.8 - 8.0
Potassium dihydrogen orthophosphate / sodium hydroxide	5.8 - 8.00
Barbitone sodium / Hydrochloric acid	6.8 - 9.6
Tris (hydroxylmethyl) aminomethane / Hydrochloric acid	7.0 - 9.00
Sodium tetraborate/ Hydrochloric acid	8.1 - 9.2
Glycine/ Sodium hydroxide	8.6 - 10.6
Sodium carbonate/ Sodium hydrogen carbonate	9.2 - 10.8
Sodium tetraborate/ Sodium hydroxide	9.3 - 10.7
Sodium bicarbonate / Sodium hydroxide	9.60 - 11.0
Sodium hydrogen orthophosphate / Sodium hydroxide	11.0 - 11.9
Potassium chloride/ Sodium hydroxide	12.0 - 13.0

Preparing a Buffer Solution ²

This page gives tabulated info on the preparation of buffers by mixing adjusters
with a known volume of the primary salt solution.

BUFFERS 1.00 - 9.00

Buffer A : pH 1.0 - 2.2		Buffer B : pH 2.2 - 4.00		Buffer C : pH 4.10 - 5.90		Buffer D : pH 5.8 - 8.00		Buffer E : pH 7.0 - 9.00
50 ml 0.2 M KCl + mls of 0.2 M HCl		100 ml 0.1 M potassium hydrogen phthalate + mls of 0.1 M HCl.		100 ml 0.1 M potassium hydrogen phthalate + mls of 0.1 M NaOH		100 ml 0.1 M KH2PO4 + mls of 0.1 M NaOH.		100 ml 0.1 M tris (hydroxymethyl) aminomethane + mls of 0.1 M HCl.
pH	mls of 0.2M HCl added	pH	mls of 0.1M HCl added	pH	mls of 0.1M NaOH added	pH	mls of 0.1M NaOH added	pH	mls of 0.1 M HCl added
1.00	134.0	2.20	99.0	4.10	2.6	5.80	7.2	7.00	93.2
1.10	105.6	2.30	91.6	4.20	6.0	5.90	9.2	7.10	91.4
1.20	85.0	2.40	84.4	4.30	9.4	6.00	11.2	7.20	89.4
1.30	67.2	2.50	77.6	4.40	13.2	6.10	13.6	7.30	86.8
1.40	53.2	2.60	70.8	4.50	17.4	6.20	16.2	7.40	84.0
1.50	41.4	2.70	64.2	4.60	22.2	6.30	19.4	7.50	80.6
1.60	32.4	2.80	57.8	4.70	27.2	6.40	23.2	7.60	77.0
1.70	26.0	2.90	51.4	4.80	33.0	6.50	27.8	7.70	73.2
1.80	20.4	3.00	44.6	4.90	38.8	6.60	32.8	7.80	69.0
1.90	16.2	3.10	37.6	5.00	45.2	6.70	38.6	7.90	64.0
2.00	13.0	3.20	31.4	5.10	51.0	6.80	44.8	8.00	58.4
2.10	10.2	3.30	25.8	5.20	57.6	6.90	51.8	8.l0	52.4
2.20	7.8	3.40	20.8	5.30	63.2	7.00	58.2	8.20	45.8
		3.50	16.4	5.40	68.2	7.10	64.2	8.30	39.8
		3.60	12.6	5.50	73.2	7.20	69.4	8.40	34.4
		3.70	9.0	5.60	77.6	7.30	74.0	8.50	29.4
		3.80	5.8	5.70	81.2	7.40	78.2	8.60	24.4
		3.90	2.8	5.80	84.6	7.50	82.2	8.70	20.6
		4.00	0.2	5.90	87.4	7.60	85.6	8.80	17.0
						7.70	88.4	8.90	14.0
						7.80	90.6	9.00	11.4
						7.90	92.2
						8.00	93.4

BUFFERS 08 - 13

Buffer F: pH 8.0 - 9.10		Buffer G : pH 9.2 - 10.80		Buffer H : pH 9.60 - 11.00		Buffer I : pH 10.90 - 12.00		Buffer J : pH 12.00 - 13.00
100 mL 0.025 M Na2B4O7.10H2O (borax) + mls of 0.1 M HCl.		100 mL 0.025 M Na2B4O7.10H2O (borax) + mls of 0.1 M NaOH.		100 mL 0.05 M NaHCO3 + mls of 0.1 M NaOH.		100 mL 0.05 M Na2HPO4 + mls of 0.1 M NaOH.		50 mL 0.2 M KCl + volume indicated (in mL) 0.2 M NaOH.
pH	mls of 0.1M HCl added	pH	mls of 0.1M NaOH added	pH	mls of 0.1M NaOH added	pH	mls of 0.1M NaOH added	pH	mls of 0.2M NaOH added
8.00	41.0	9.20	1.8	9.60	10.0	10.90	6.6	12.00	12.0
8.10	39.4	9.30	7.2	9.70	12.4	11.00	8.2	12.10	16.0
8.20	37.6	9.40	12.4	9.80	15.2	11.10	10.2	12.20	20.4
8.30	35.4	9.50	17.6	9.90	18.2	11.20	12.6	12.30	25.6
8.40	33.2	9.60	22.2	10.00	21.4	11.30	15.2	12.40	32.4
8.50	30.4	9.70	26.2	10.10	24.4	11.40	18.2	12.50	40.8
8.60	27.0	9.80	30.0	10.20	27.6	11.50	22.2	12.60	51.2
8.70	23.2	9.90	33.4	10.30	30.4	11.60	27.0	12.70	64.4
8.80	19.2	10.00	36.6	10.40	33.0	11.70	32.4	12.80	82.4
8.90	14.2	10.10	39.0	10.50	35.6	11.80	38.8	12.90	106.0
9.00	9.2	10.20	41.0	10.60	38.2	11.90	46.0	13.00	132.0
9.10	4.0	10.30	42.6	10.70	40.4	12.00	53.8
		10.40	44.2	10.80	42.4
		10.50	45.4	10.90	44.0
		10.60	46.6	11.00	45.4
		10.70	47.6
		10.80	48.5

Acetate buffer solutions pH 3 - 6 ³

Make up the following solutions
(1) 0.1M acetic acid
(2) 0.1M sodium acetate (tri-hydrate) (13.6g / l)
Mix in the following proportions to get the required ph

ph	vol. of 0.1M acetic acid	vol. of 0.1M sodium acetate
3	982.3 mls	17.7 mls
4	847.0 mls	153.0 mls
5	357.0 mls	643.0 mls
6	52.2 mls	947.8 mls

Phosphate buffer solutions ph 7 - 11

Make up the following solutions
(1) 0.1M disodium hydrogen phosphate (14.2g / l)
(2) 0.1M HCl
(3) 0.1M NaOH
Mix in the following proportions to get the required ph

pH	vol. of phosphate	vol. of 0.1M HCl	vol. of 0.1M NaOH
7	756.0 mls	244 mls
8	955.1 mls	44.9 mls
9	955.0 mls	45.0 mls
10	966.4 mls		33.6
11	965.3 mls		34.7

Addition of acid or base to a salt pH 3 - 11

Here, the primary salt is a solid and is weighed out in grams. A measured amount of 0.1M HCl or NaOH is added,
then made up to 1 liter to give the relevant buffer solution ⁴.

pH	Salt mixture Dilute each mixture to 1 liter solution with distilled water
3	10.21g potassium hydrogen phthalate and 223ml of 0.01M HCl
4	10.21g potassium hydrogen phthalate and 1ml of 0.01M HCl
5	10.21g potassium hydrogen phthalate and 226ml of 0.01M NaOH
6	6.81g potassium dihydrogen phOsphate and 56ml of 0.01M NaOH
7	6.81g potassium dihydrogen phosphate and 291ml of 0.01M NaOH
8	6.81g potassium dihydrogen phosphate and 467ml of 0.01M NaOH
9	4.77g sodium tetraborate and 46ml of 0.01M HCl
10	4.77g sodium tetraborate and 183ml of 0.01M NaOH
11	2.10g sodium bicarbonate and 227ml of 0.01M NaOH

1. The Physical and Theoretical Laboratory, Oxford University.
2. "Electrolyte solutions" Robinson, R. A., and Stokes, R. H., 2nd ed., rev. London, Butterworths, 1968.
3. "Practical chemistry" J. Lambert and T.A. Muir, 3rd. Ed. Heineman, London.
4. pdf file, www.bc.ca/bcsc/resources/ (Canadian Teachers Federation).