To make 100 ml of 100 mM Tris-HCl (Mw = 121.14) pH 8, 100 mM NaCl (Mw = 58.44) y

ID: 512292 • Letter: T

Question

To make 100 ml of 100 mM Tris-HCl (Mw = 121.14) pH 8, 100 mM NaCl (Mw = 58.44) you would

A. add 1.21 g Tris and 0.5844 g NaCl to a beaker, pH to 8.0 with HCl, bring up to 100 ml.

B. Add 121 g Tris and 58.44 g NaCl to a beaker, pH to 8.0 with HCl, bring up to 100 ml.

C. add 1.21 g Tris and 0.5844 g NaCl to a beaker, bring up to 100 ml, pH to 8.0 with HCl.

D. add 1.21 g Tris to a beaker, pH to 8.0 with HCl, add 0.5844 g NaCl to the beaker, re-pH to 8.0 with HCl, bring up to 100 ml.

E. add 12.1 g Tris and 5.844 g NaCl to a beaker, pH to 8.0 with HCl, bring up to 100 ml.

A) is correct.

Step 1- Calculate the mass of 100mM Tris-HCl

Molar mass of Tris-HCl = 121.14 g/mol

Volume of Tris-HCl = 100 ml

Concentration of Tris-HCl = 100mM = 0.1M

This means

1MTris-HCl = 121.14g/1000ml

1000 ml1M solution contains 121.14g of Tris-HCl

100 ml 1M solution contains 121.14 x (100/1000) = 12.1g Tris-HCl

100 ml 0.1 M solution contains 12 .1g x (0.1M /1M) = 1.21 g Tris-HCl

Step 1- Calculate the mass of 100mM NaCl

Mw of NaCl = 58.44 g/mol

Volume of NaCl = 100 ml

Concentration of NaCl = 100mM = 0.1M

This means

1M NaCl = 58.44g/1000ml

1000ml 1M solution contains 58.44g of NaCl

100 ml 1M solution contains 58.44 x (100/1000) = 5.844g NaCl

100 ml 0.1 M solution contains 5.844g x (0.1M/1M) = 0.5844 g NaCl

Add 1.21 g Tris and 0.5844 g NaCl to a beaker, pH to 8.0 with HCl, bring up to 100 ml.

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