In a laboratory experiment, a 10.0 mL sample of NaCl solution ispoured into an e

Question

In a laboratory experiment, a 10.0 mL sample of NaCl solution ispoured into an evaporating dish with a mass of 22.00 g. Thecombined mass of the evaporating dish and NaCl solution is 37.55 g.After heating, the evaporating dish and dry NaCl have a combinedmass of 25.00 g.

Part A
What is the %m/m of the NaCl solution


Part B
What is the Molarity of the NaCl solution

Part C
If water is added to 10.0 mL of the initial NaCl solution to give afinal volume of 78.0 mL, what is the molarity of the dilute NaClsolution?

Explanation / Answer

Given: Volume of NaCl solution = 10.0mL Mass of evaporating dish = 22.0g Mass of dish + NaCl solution = 37.55g Mass of dish + NaCl solid = 25.00g So, mass of NaCl solution = 37.55g - 22.00g =15.55g Density of soluiton = 15.55g / 10.0mL =1.555g/mL Mass of NaCl solid = 25.00g - 22.00g = 3.00g Mass percent of NaCl = (3.00g / 15.55g )*100 = 19.29% ---------------- Molarity, M = density / molar mass                   = 1.555g/mL / (58.442g/mol)                    = (1.555g / 58.442g)mol/mL                    = 0.02661mol /mL                    = 26.61mol / L    = 26.61M -------------------- We know that, MfVf = MiVi Mf = MiVi / Vf        = (26.61M)(10.0mL) /(78.0mL)        = 3.41M Hence, final molarity is 3.41M

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