Show all work. A solution made to be 20.2% HCl by mass in water has a density of
ID: 843746 • Letter: S
Question
Show all work.
A solution made to be 20.2% HCl by mass in water has a density of 1.096 g/mL. Calculate the molarity and molality of the HCl in solution. Calculate the expected boiling point of a solution of 238 g of KBr added to 3.00 kg of water. For water, Kb is equal to 0.512 degree C/m. As a solution of KBr and water boils, only the water molecules will vaporize. What should happen to the boiling point temperature overtime as such a solution boils? Explain. As a KBr and water solution begins to freeze, water molecules will tend to become organized into the pure ice crystal structure excluding the K + and Br- ions which stay mixed with the remaining liquid water. Eventually, the remaining liquid water will be saturated with KBr and solid KBr will precipitate. Thus the freezing process, if performed slowly, may separate the water from the KBr. What should happen to the freezing point temperature during the early stages of the process? Explain.Explanation / Answer
1)
Let us take 1000 gm of solution ,
volume of solution = mass/ density = 1000/1.096 = 912.4087 mL = 0.9124087 L
mass of HCl = 1000 * (20.2/100) = 202 gm
moles of HCl = 202/36.5= 5.5342 moles
mass of water = 1000-202 = 798 gm
moles of water = 798/18 = 44.3333 moles
molarity = moles of HCl/ volume of solution = 5.5342/0.9124087 = 6.065483 M
molality = moles per Kg of solution = 5.5342 moles/Kg
2)
total weight of solution = 238 + 3000 = 3238 gm
moles of KBr = 238/119.002 = 2
molality = 2/ 3.238 = 0.617665 moles/Kg
expected boiling point = 100 + (Kb * m) = 100 + ( 0.617665 * 0.512) = 100.31624 C
3)
As the solution keeps boiling the water molecules leave the solution and become vapour and the molality of KBr in the solution keeps on increasing, as a result the boiling point of solution keeps on increasing over the time.
4)
The freezing point decreases , because even at 0 C some of the water will be saturated with KBr and does not form ice, for all the water to form ice, the KBr present in it has to completely precipitate, thus we need to go down below 0 C for all the KBr to precipitate and the water to freeze.