How Are Buffers Made?

Home » What Makes A Good Buffer » How Are Buffers Made?

Maybe your like

How are buffers made?

A buffer must contain a weak acid and its conjugate base. There are several ways a solution containing these two components can be made:

Buffers can be made from weak acids or base and their salts. For example, if 12.21 grams of solid sodium benzoate are dissolved in 1.00 L 0.100 M benzoic acid (C6H5COOH, pKa = 4.19) solution, a buffer with a pH of 4.19 will result:

Buffers can be made from two salts that provide a conjugate acid-base pair. A buffer can be made by dissolving 15.0 grams NaH2PO4 and 17.7 grams Na2HPO4 in water and diluting to 1.00 liter.

What will be the pH of this buffer (molecular weight of NaH2PO4 is 120.0 g/mol, molecular weight of Na2HPO4 is 142.0 g/mol)?

H3PO4 + H2O H2PO4- + H3O+ Ka1 = 7.1 x 10-3 H2PO4- + H2O HPO42- + H3O+ Ka2 = 6.3 x 10-8 HPO42- + H2O PO43- + H3O+ Ka3 = 7.1 x 10-13

2.14 7.10 12.15

The acid in this buffer is H2PO4- and the conjugate base is HPO42-. Which ionization reaction is an equilibrium between these two species?

Good!

Buffers can be made by adding a strong acid or base to a weak acid or base. If a strong acid such as HCl is added to NH3 (a weak base), NH4+ (the conjugate acid of NH3) is produced:

H+ + NH3 NH4+

If 50.0 mL 0.10 M HCl is added to 100.0 mL 0.10 M NH3, what are the resulting concentrations of NH3 and NH4+?

[NH3] = 0.10 M [NH4+] = 0 M [NH3] = 0.10 M [NH4+] = 0.10 M [NH3] = 0.10 M [NH4+] = 0.05 M [NH3] = 0.05 M [NH4+] = 0.05 M

The added HCl will react with NH3 to produce NH4+. How many moles of HCl are added? How many moles of NH4+ will be produced? How many moles of NH3 will remain?

Good!

Tag » What Makes A Good Buffer