Without any solid separating. The solution is (A) supersaturated at 75 degree C.

Question

Without any solid separating. The solution is (A) supersaturated at 75 degree C. (B) supersaturated at 15 degree C. (C) unsaturated at 15 degree C. (D) saturated at 15 degree C. A mixture of 100 g of K_2CrO_7 and 200 g of water is stirred at 60 degree C until no more of the salt dissolves. The resulting solution is poured off, leaving the undissolved solid behind. The solution is now cooled to 20 degree C. What mass of K_2Cr_2O_7, crystallizes from the solution during the cooling? (A) 24 g (B) 31 g (C) 43 g (D) 62 g What mass of water is needed to dissolve 292.5 g of NaCI to produce a 0.25 m aqueous solution? (A) 20 kg (B) 5.0 kg (C) 0.80 kg (D) 0.050 kg What is the mole fraction of water in 200. g of 95% (by mass) ethanol, C_2H_5OH? (A) 0.050 (B) 0.12 (C) 0.56 (D) 0.88

Explanation / Answer

23. Molar mass of ethanol Me = 46 g.mol-1

Molar mass of water Mw = 18 g.mol-1

Total mass of solution ms = 200 g

Mass percent of ethanol is 95%, so mass fraction of ethanol is 0.95

Mass fraction of water is 1 - 0.95 = 0.05

Mass of ethanol = Mass fraction of ethanol x Total mass

= 200 x 0.95

=190 g

Mass of ethanol = 190 g

Moles of ethanol = Mass of ethanol/ molar mass of ethanol

=190/46

=4.13 moles

Moles of ethanol = 4.13 moles

Mass of water = Total mass - mass of ethanol

= 200-190

=10 g

Mass of water = 10 g

Moles of water = Mass of water/Molar mass of water

=10/18

=0.56 moles

Moles os water = 0.56 moles

Total moles = Moles of ethanol + Moles of water

= 4.13 + 0.56

=4.69 moles

Total moles = 4.69 moles

Mole fraction of water = moles of water / total moles

= 0.56/4.69

=0.12

Mole fraction of water = 0.12

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.