Question

Chemistry calculations, please show all work

How do you prepare the following solutions?

1) 2L solution of 20% methanol. FW=32.06g/mol

2) 2L solution of 150mM MOPS. FW=209.26g/mol

3) how would you prepare 1L of 5X stock solution of 0.15M sodium phosphate buffer (use Na2HPO4) FW=141.96g/mol

Answer 1

1. 20% solution means 20 ml of methanol in 100 ml of water

So, in 1 L or 1000 ml solution, amount of methanol= 200 ml

for 2L solution or 2000 ml, amount of methanol= 200+200 = 400 ml

400 ml of methanol is dissolved in water to make the volume upto 2000 ml.

2. 2L solution of 150mM MOPS.

Molarity= 150mM or 0.15 M

molarity = moles/ volume of solution in litres

moles= molarity*volume of solution in litres= 0.15*2= 0.3

weigt= moles*molar mass= 0.3*209.26 = 62.7 gm

62.7 gm of MOPS dissolved in 2 L of water to make 150mM solution.

3. Moles of Na2HPO4= molarity* volume in L = 0.15*1= 0.15 moles

Dilution to 5 times= 0.15*5= 0.75

weight= moles*molar mass = 0.75*141.96= 106.47 gm