. A 10.0-mL sample of a saltwater solution containing sodium chloride, NaCl, was

Question

. A 10.0-mL sample of a saltwater solution containing sodium chloride, NaCl, was evaporated to dryness and gave the following data: mass of evaporating dish + solution mass of evaporating dish mass of evaporating dish + NaCl 51.925g 41.697 g 42.208 g (a) Refer to Example Exercise 19.1 and show the calculation for the mass/mass percent concentration of NaCl in the saltwater sample. (b) Refer to Example Exercise 19.2 and show the calculation for the molar concentration of NaCl (58.44 g/mol) in the saltwater sample. 6. What are major sources of experimental error in analyzing the saltwater solution?

Explanation / Answer

Question 5.

The mass of saltwater solution = (mass of evaporating dish + solution) - mass of evaporating dish

= 51.925 - 41.697 = 10.228 g

The mass of NaCl = (mass of evaporating dish + NaCl) - mass of evaporating dish

= 42.208 - 41.697 = 0.511 g

a) The mass percent concentration of NaCl in the saltwater sample = (mass of NaCl/mass of saltwater solution)*100

= (0.511 g/10.228 g)*100

= 4.996 ~ 5 %

b) The no. of moles of NaCl = 0.511 g/(58.44 g/mol) = 0.008744 mol = 8.744 mmol

Now, the molar concentration of NaCl = no. of mmol/volume (mL) = 8.744 mmol/10 mL = 0.8744 M

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