Question

Which of the following should be done in preparing 0.50 m Naci from 100 mL of 0.30 M Naa (molecular wt. of NaCl-58.5) ?

1) Add 5.85g Nac mol
2) Add 20 ml water
3) Add 0.010 mol Nad
4) Evaporate 10 ml water

Answer 1

To prepare a 0.50 M NaCl solution from 100 mL of 0.30 M Na, none of the provided options are correct. The correct procedure involves calculating the needed mass of NaCl and dissolving it in water to maintain the volume at 100 mL.

Step-by-step explanation:

The question pertains to the preparation of a sodium chloride (NaCl) solution of a targeted molarity. The student is given a solution of sodium (Na) at a specific concentration and needs to adjust it to achieve a 0.50 M concentration of NaCl in a volume of 100 mL.

Step-by-Step Solution:

First, we need to calculate the number of moles of NaCl required for the desired molarity and volume:
moles of NaCl = Molarity (M) × Volume (L) = 0.50 M × 0.100 L = 0.050 moles.

Next, calculate the mass of NaCl needed:
mass of NaCl = moles × molar mass = 0.050 moles × 58.5 g/mol = 2.925 g.

To prepare the solution, dissolving the calculated mass of NaCl in water to achieve a final volume of 100 mL is required. The options provided do not include this exact procedure. Adding 5.85 g of NaCl (option 1) exceeds the required mass, diluting with an additional 20 mL of water (option 2) would alter the final volume and molarity, and adding 0.010 moles of Na (option 3) does not take into account the conversion to NaCl. Option 4, evaporating water, would increase the concentration of the existing solutes rather than altering the Na concentration to NaCl.