[rami]

Q1) A solution of XCl₃ has a molality of 1.3mol/kg and a molarity of 1.24 mol/dm³.
density= 1.12g/cm³.Find the mass of X.

2)Two solutions A and B of concentrations 10% and 30% were mixed to obtain solution C.Calculate the amount of solutions A and B needed to get a solution C of concentration 15% .


here's how i tried to solve Q1),
molecular mass of XCl₃ = x+ (3*35.5) = (x + 106.5 ) g
mass of XCl₃ = 1.3(x+106.5)

and provided we have 1000g of water, mass of solution = 1000+  1.3(x+106.5) =y
then the volume of solution will be= y/1.12
but i'm not sure how to proceed from here and how i'm supposed to use the molarity to solve this..


For 2) I honestly don't know how to begin.could someone tell me how?

THANK YOU
 

[MrTeo]

a) Seems OK to me ^^

b) Use the definition of mass/mass percentage (I suppose you're talking about that), when we mix two solutions we sum their volumes and the amounts of the compunds solved: so?

[llagetias]

For question 1

If you multiply the density by the molarity making sure to convert dm^3 to cm^3, then you will have the term for moles of XCl3 over mass of soln

1.24 mol/dm^3 X 1 dm^3/1000 cm^3 X (cm^3/1.12 g) =  moles of XCl3/mass of soln

You take what this term equals and set it equal to the molality times the mass of water over the term you came up with for the mass of soln and solve for x. I think then you should get your answer.

For question 2

Does the problem ask for the concentration of C in terms of A and B? Or are there numbers that go along with it?
If it is in terms of A and B, you should probably just make a relation by summing A and B multiplied by their respective fractions and set it equal to C and multiply the term to get the appropriate percentage of C.

I hope this helps.

[AWK]

Q1) Find mass of 1.24 molar solution that contains 1.30 mole of compound. This contains 1.30 mole of XCl₃ and 1.00 kg of water

2) mass balance
0.10xm_A + 0.30xm_B = 0.15x(m_A+m_B)      (= 0.15xm_C)

[rami]

Q1) Find mass of 1.24 molar solution that contains 1.30 mole of compound. This contains 1.30 mole of XCl₃ and 1.00 kg of water

2) mass balance
0.10xm_A + 0.30xm_B = 0.15x(m_A+m_B)      (= 0.15xm_C)

Thanks!Managed to do Q1.Here's how,
[100+1.3(x + 106.5)]/1.12 = 1.3*1000/1.24
and got 27.5g as the mass of X after solving.Hope it's correct..

But I still find it hard to solve question 2).Can you please explain how we can find the amount of solutions A and B needed,from the equation you provided?

For question 2

Does the problem ask for the concentration of C in terms of A and B? Or are there numbers that go along with it?
If it is in terms of A and B, you should probably just make a relation by summing A and B multiplied by their respective fractions and set it equal to C and multiply the term to get the appropriate percentage of C.

I hope this helps.

Thanks but I think our teacher expects us to find a value for the amounts,not in terms of A and B.There weren't any other numbers given in the question either

[sjb]

I suppose, from the forum that you've posted this in, that you are to assume that volumes are completely additive, and ideal solutions. So 1 gallon of solution A plus 1 gallon of solution B makes 2 gallons of mixture. Can you calculate the concentration of this mixture?

[rami]

Thank you all for replying,but I just can't seem to figure this out.Are all of you suggesting the same thing?sorry but I'm a little confused .

And I'm not even sure I understand the question.em...so the values given in the question are the mass percentages of solutions A & B and using these 2 solutions we are to make solution C of mass percent 15,right ? Therefore solution C will have a mass of m₁ + m₂ where m₁=mass of A & m₂ = mass of B. And the total volume of C= V₁+V₂ ? so how do I use this to calculate the amounts needed ?

[AWK]

You should assume the mass of solution C eg. 100 grams. Then you have the second equation
m1 + m2 = 100.
After finding m1 and m2 you can calculate ratio m1/m2. Usually this is variable that should be find in this type of calculations. Note - this should be stated in question!