Question

1. Express 2.5M NaCl as a percent solution.

What is the molar concentration of a 10% NaCl solution?

2. from a 1M Tris solution, how is a 400ml of 0.2M Tris is prepared?

3. What is the molarity of a solution of sucrose that has a density of 1.24 g/ml and a molecular weight of 342.3 g/mol.

4. Forty micoliters of a stock solution of RNA is diluted with water to give a final volume of 1000 microliters. The diluted sample has an absorbance at 260nm of 0.142. What is the concentration of the concerntration of the RNA stock solution in micro grams/milliliter.

5. from a small culture, you have purified the DNA of a rocombinant plasmid. You have resuspended the DNA in a volume of 50 microliter. You dilute 20 of the purified DNA sample into a total volume of 1000 microliter distilled water. You measre the absorbance of this diluted sample at 260 nm and 280 nm and obtain the following readings.

A260=0.550

A280=0.324

a. What is the DNA concentration of the 50microliter plasmid prep?

b. How much total DNA was purified by the plasmid preparation?

c. What is the A260/A280 ratio of the purified DNA?

Answer 1

I'm just going to answer 1, 2 and 3. There are multiple questions here.

1 and 2)

3 ) 1.24 g/ml = 1240 g/l

M = 1240 g/l / 342.3 g/mol = 3.6 mol /l = 3.6 M