1a. A student is given 400 ml of a 3 M solution of NaCl and told to make 1,000 m

Question

1a. A student is given 400 ml of a 3 M solution of NaCl and told to make 1,000 ml of a .5M NaCl solution. How much H2O must be added to how ml of the original solution to arrive at exactly 1,000 ml of .5M NaCl? (NaCl MW is 58.4g)

b. A 475 ml flask of a 2M NaCl is inadvertently left on a hot plate over night by a careless student. When the flask is finally removed, its final volume is only 125 ml. What is the molarity of the solution left in the flask? (NaCl MW is 58.4g)

c. How much 3M H2SO4 would be needed to make 500 ml of 0.1M H2SO4?

PLEASE SHOW ALL WORK

Explanation / Answer

when a solution is diluted , we are adding solvent only but not solute. thus the moles /mmoles of solute remain constant before and after dilution.

Thus (VM) before = (VM) after dilution as VxM = number of moles of solute

1a) you have 400mL of 3M NaCl stock solutio. You need to prepare 100mL of 0.5M solution.

Let the volume of 3M solution to be diluted be V mL

Then V x 3M = 1000 mLx 0.5M

thus V = 166.67 mL

Hence 166.67mL of 3M NaCl solution to be diluted to 1000mL of 0.5M solution by adding (1000-166.67) =833.33 mL of water.

1b) Initial volume = 475mL and M = 2M

Now th volume is 125 mL

475mL x 2 M= 125 mL xM

thus new molarity= 7.6M

1c)

VmL x 3M = 500 x 0.1 M

Thus V = 16.67mL

16.67mL of 3M H2SO4 to be diluted to 500mL of 0.1M solution.

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