Q1) Calculate the mass of nitrogen dissolved at room temperature in an 77.0 L ho
ID: 893239 • Letter: Q
Question
Q1) Calculate the mass of nitrogen dissolved at room temperature in an 77.0 L home aquarium. Assume a total pressure of 1.0 atm and a mole fraction for nitrogen of 0.78.
Express your answer using two significant figures
Q2) Magnesium citrate, Mg3(C6H5O7)2, belongs to a class of laxatives called hyperosmotics, which are used for rapid emptying of the bowel. When a concentrated solution of magnesium citrate is consumed, it passes through the intestines, drawing water and promoting diarrhea, usually within 6 hours.
Calculate the osmotic pressure of a magnesium citrate laxative solution containing 29.5 g of magnesium citrate in 254 mL of solution at 37 C (approximate body temperature). Assume complete dissociation of the ionic compound.
Q3)An aqueous NaCl solution is made using 120 g of NaCl diluted to a total solution volume of 1.15 L .
a)
Calculate the molarity of the solution.
Express your answer using three significant figures.
B)
Calculate the molality of the solution. (Assume a density of 1.08 g/mL for the solution.)
Express your answer using two significant figures.
C)
Calculate the mass percent of the solution. (Assume a density of 1.08 g/mL for the solution.)
Express your answer using three significant figures.
Q4)
To what volume should you dilute 56.5 mL of a 4.45 M KI solution so that 23.5 mL of the diluted solution contains 3.20 g of KI?
Q5)
Lead is a toxic metal that affects the central nervous system. A Pb-contaminated water sample contains 0.0013 % Pb by mass.
How much of the water (in mL) contains 145 mg of Pb? (Assume a density of 1.0 g/mL.)
Express your answer using two significant figures.
Explanation / Answer
Ans (1)
Given,
Pressure = 1 atm; mole fraction of nitrogen = 0.78, volume of aquarium = 77.0 L
As we know, Henry's law constant (kH) for nitrogen is = 0.00061 M or 6.1*10-4 M
Now convert n moles of nitrogen to grams = n moles/77.0 L = 0.00061 M /atm * 1 atm
n = 0.045 moles
As 1 mole of nitrogen contains = 28 gm N2 (molecular weight of N2 )
so 0.045 moles of nitrogen contains = 28 gm * 0.045 moles
= 1.26 gm
mass of nitrogen = 1.26 gm * 0.78
= 0.983 gm
Partial pressure of N2 is p = (0.78)(1.0atm). In the 80 L tank there is, by the ideal gas law PV = nRT,
n = PV / RT = (0.78 atm)(80 L) / { (0.08206 L*atm/K*mol)(21.1+273.2 K) }
m = n * MW(N2)
where MW is the molecular weight of nitrogen gas. (NB: Your room may be cooler than mine.)
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