Sample Calculations II

1. Make a 50 ml agarose gel of 0.8% that is 0.5X TBE. The TBE (Tris FW = 121.1, Borate FW = 61.8, EDTA FW = 372) stock is 10X.

0.4 g agarose

2.5 ml 10X TBE stock

47.5 ml H₂O

2. You have a 150X stock of buffer and you need 2.5 ml of 1X. How do you make this?

16.6 µl 150X stock plus 2.484 ml H₂O

3. You have a DNA solution that is 21.3 µg/µl and you want 75 µl that is 50 ng/µl. How do you make this?

0.176 µl DNA stock solution + 74.824 µl H₂O

4. Make 350 ml of a solution that is 25 mM Tris, 2.5 mM EDTA, and the pH is 8.0.
Tris is a base and the FW of Tris is 121.1 and EDTA is 187. Do not make a volume that exceeds 350 ml!!

1.06 g Tris

0.16 g EDTA

275 ml H₂O

pH with HCl and bring up to 350 ml with H₂O

5. Make two solutions of 100 ml each: A is 125 mM Na₂HPO₄^. 7H₂O (FW = 268) and B is 0.25 M NaH₂PO₄ (FW = 120). When you mix them in this ratio (2 parts water, 1 part A, and 0.5 parts B) what will the final molarity be for each one in this mixture?

3.35 g Na₂HPO₄^. 7H₂O

3.0 g NaH₂PO₄

dissolve each in water and then bring each one up to 100 ml

A will be 35.7 mM and B will also be 35.7 mM

6. Make 200 ml of a 15 mM Tris, 50 mM EDTA, and 0.03 M NaCl from stock solutions that are 1M Tris, 0.5 M EDTA, and 5000 mM NaCl.

20 ml EDTA

3.0 ml Tris

1.2 ml NaCl

176.8 ml H₂O

7. You are making a PCR mixture that will be 1 X of all reagents and the final volume will be 200 µl. How do you with these stocks?

300X solution A 0.67 µl

1500 X B 0.13 µl

200X C 1.0 µl

25X D 8.0 µl plus 190.2 µl H₂O

8. The protocol calls for a solution that is 1.5 % (w/v) NaCl, 2mM Tris (pH 8.0), 7% (w/v) powdered milk (you think I'm making this up?), and 0.02% (v/v) antifoam A. Is it possible to make this solution? If so, how?

15 g NaCl

0.242 g Tris

70 g dry milk

200 µl anti-foam A

pH to 8.0 with HCl and add water up to 1 L

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