Question

10 mL.H,O (d=1 g/mL) is mixed with 4 mL methyl alcohol (d =0.8 g/mL) and if the final solution
has the density 1.1 g/mL, then calculate Molarity 'M' of alcohol solution.
(A) 8.43 M . (B) 8.33 M
(C) 8.53 M
(D) 8.63 M​

Answer 1

Answer:

this is an example

example question  :  

Can you help me with this? 20 g of glucose is dissolved in 150 g of water. Calculate the molarity, molality & mole fraction of glucose in solution.

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Explanation:

answer of the above example question :

The problem gives you all the information you need in order to solve for the molality and mole fraction of the solution. In order to determine its molarity, you're going to need the solution's volume.

To get the volume, you have to know what the density of the solution is. Determine the percent concentration by mass of the solution first

%W / W = $\frac{M solute}{M solution} . 100$

in this case , the mass of solution will be

M solution = Mglucose + Mwater

Msolution = 20+150 =170g

this means that you get

%W / W = $\frac{20 g}{ 170 g} . 100 = 11.8 %$

The density of this solution will thus be

170 g .$\frac{1 mL}{1.045 g} = 162.7 mL$

This means that its molarity is - do not forget to convert the volume to liters!

$C =\frac{n}{V} = \frac{0.111 moles}{162 . 10^{-3} L}$ = 0.68 M

A solution's molality is defined as the number of moles of solute divided by the mass of the solvent - in kilograms! This means that you have

$b = \frac{n}{M water} = \frac{0.111 moles}{150.10^{-3} Kg}$ = 0.74 molal

To get the mole fraction of sucrose, you need to know how many moles of water you have present. Once again, use water's molar mass

150 g . $\frac{1 Mole Water }{18.02 g } = 8.24 moles water$

The total number of moles the solution contains is

$N total = N glucose + N water\\\\N total = 0.111 + 8.24 = 8.351 moles$

This means that the mole fraction of sucrose, which is defined as the number of moles of sucrose divided by the total number of moles in the solution, will be

X surcose = $\frac{ N surcose}{N total } = \frac{0.111 moles}{8.351 moles} = 0.013$