Question

If you needed to make 500 mL of  a TBE buffer (containing 0.1M Tris base, 0.1M Boric Acid, and 0.02M EDTA) how much of each of the following would you use: solid Tris base (121.1 g/mol); solid boric acid (61.8 g/mol); liquid stock solution of 0.50M EDTA?

Answer 1

Volume of buffer = 500 ml or 0.5 L

0.1 M Tris

Moles of Tris = 0.1 M * 0.5 L

= 0.05 mol

Mass of Tris to be added = 0.05 mol * 121.1 g /mol

= 6.06 g

0.1 M Boric acid

Moles of Boric acid = 0.1 M * 0.5 L

= 0.05 mol

Mass of Boric acid to be added = 0.05 mol * 61.8 g/mol

= 3.09 g

0.02 M EDTA

Dilution equation:

M_stock * V_stock = M_dilution * V_dilution

V_stock = (0.02 M * 500 ml)/0.50 M

V_stock = 20 ml

So, to make 500 ml of TBE buffer, take 6.06 g of Tris base, 3.09 g of boric acid and dissolve it in 20 ml.of stock EDTA in a 500 ml volumetric flask. Now, make up the final volume to 500 ml with distilled water.