Question

measure 5 grams of sodium chloride (NaCl) and add to 50 ml of distilled water in a graduated cylinder. stir the salt. this was a failed attempt at making a 10% w/v solution. Determine the excess volume by reading the volume of the graduated cylinder. the number of ml in excess of 50 represents the volume displaced by the 5g of dissolved NaCl.

The question for the above information is: What is the actual percentage of NaCl (w/v)?

Please explain to me in detail to get to the answer. Thank you so much

Answer 1

To prepare a 10% w/v NaCl solution for 50 mL, we need to weigh 5 g of NaCl and dissolve it in 20-30 mL of water. Shake well to solubilize the salt. Make up the volume to 50 mL with water. If we directly add 5 g of NaCl to 50 mL water, it will produce less concentrated solution.

Density of NaCl = 2.16 g/mL
1 mL -----> 2.16 g
5 g -------> ___ mL ?

= 5/2.16
= 2.314 mL

So, addition of 5 g of NaCl to 50 mL water increases solution volume by 2.314 mL
Final volume = 2.314 + 50 = 52.314 mL
Total mass of NaCl = 5 g

Weight/volume = (5/52.314) X 100
= 9.5576 % w/v