Question

MW molewo one expand 4. a) Calculate the mass of NaCl needed to prepare 35.0 mL of a 0.90% w/v Naci solution b) Calculate the mass of NaCl needed to prepare 35.0 mL of a 20.0 % wly NaCl solution. c) Describe how you would make the solution for 4a. Be brief, but quantitative, in your answer.

Answer 1

PART (a):

Given that : Mass/volume percentage = 0.90 %

That means, 0.90 g of NaCl is present in every 100 mL of the solution.

Therefore, Mass of NaCl per mL of solution = (0.90 g) / (100 mL) = 0.009 g/mL

Hence, Mass of NaCl in 35 mL of solution = (0.009 g/mL) x (35 mL) = 0.315 g ------- (answer)

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PART (b):

Given that : Mass/volume percentage = 20 %

That means, 20 g of NaCl is present in every 100 mL of the solution.

Therefore, Mass of NaCl per mL of solution = (20 g) / (100 mL) = 0.2 g/mL

Hence, Mass of NaCl in 35 mL of solution = (0.2 g/mL) x (35 mL) = 7 g ------- (answer)

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PART (c):

We need to weight 0.315 g of NaCl and put it in a graduated cylinder.

Pour pure water into the graduated cylinder until it reaches the level 35 mL.

Mix it until NaCl dissolves uniformly. Now we have a 35 mL of 0.90 % w/v NaCl solution