Question

Calculate the concentration of components in a 1X TBS from the following

10X TBS (1 L)

30 g Tris base (MW 121.44)

80 g NaCl (MW 58.44)

2 g KCl (MW 74.55)

Add 800 mL water, adjust pH to 7.4

Fill to 1L with water

Answer 1

Ans. #1. Tris base:

Required quantity for 1X TBS, 1.0 L = Total required quantity / Strength

                                                            = 30.0 g / 10X

                                                            = 3.0 g / 1X

Therefore, required mass of Tris base for 1.0 L, 1X buffer = 3.0 g

Required moles = Mass/ Molar mass

                                    = 3.0 g / (121.44 g/ mol)

                                    = 0.0247 mol

Now,

            Molarity of tris-base = Moles / Volume of buffer in liters

                                                = 0.0247 mol / 1.0 L

                                                = 0.0247 M

                                                = 20.47 mM

#2. NaCl:

Required quantity for 1X TBS, 1.0 L = 80.0 g / 10X = 8.0 g/ X

Therefore, required mass of NaCl for 1.0 L, 1X buffer = 8.0 g

Required moles = 8.0 g / (58.44 g/ mol) = 0.1369 mol

Now,

            Molarity of NaOH = 0.1369 mol / 1.0 L = 0.1369 M = 136.9 mM

#3. KCl                      

Required quantity for 1X TBS, 1.0 L = 2.0 g / 10X = 0.2 g/ X

Therefore, required mass of KCl for 1.0 L, 1X buffer = 0.2 g

Required moles = 0.0 g / (74.55 g/ mol) = 0.002683 mol

Now,

            Molarity of KCl = 0.002683 mol / 1.0 L = 0.002683 M = 2.68 mM