At a camp site at high altitude, you start to cook a stew, so you sun a fire and

Question

At a camp site at high altitude, you start to cook a stew, so you sun a fire and boil 3,000 kg water. Using a thermometer, you find that the water boils a: 94.85 degree C at the camp site. The normal boiling point of water is 100.0 degree C and its Delta Hvap = 2260 kJ/kg. What is the pressure at the high-altitude camp site? After the water boils, you attempt to season the stew using table salt (assume 100% NaCl). However, because you only have a shaker, you add an unknown amount of salt into the boiling water. You want to know how much salt you added to the water. You measure that the new boiling point is now 95.00 degree C. How much NaCl did you end up adding to the boiling water? The kb of water is 0.512 degree C/molal.

Explanation / Answer

1) ln (P2 / P1) = (delta H / R) x (1/T1 - 1/T2)

delta H = 2260 KJ/Kg = 2260 / 55.555 = 40.68 KJ/mole = 40680 J/mol

=> ln (P2 / 1) = (40680 / 8.314) x (1/373 - 1/367.85)

=> P2 = 0.8322 atm

b)

Partial Pressure of CO2 = K x concentration

=> Concentration1 (in atmosphere) = 3.33 x 10^-4 / 29.41 = 1.1323 x 10^-5 moles/L

=> Conc. at Height = 3.33 x 10^-4 x 0.8322 / 29.41 = 9.4227 x 10^-6 moles/L

Change= 1.1323 x 10^-5 moles/L - 9.4227 x 10^-6 moles/L = 1.9 x 10^-6 M

c)

Rise in BP = 0.15

0.15 = 0.512 x m

=> m = 0.293 molal

0.293 moles of NaCl in 1 Kg water

=> 0.293 x 3 = 0.879 moles of NaCl in 3 Kg water

=> Mass of NaCl = 0.879 x 58.5 = 51.422 g NaCl added

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