Density of Solution and mass percent

In summary, the density of Methanol is 0.793 kg/l. The concentration of H2SO4 is 98% by mass having density of 1.84gm/ml. Calculate Molarity.
  • #1
harman90
22
0
There are two numericals,

1. Density of Methanol is 0.793 kg/l. Find molarity. ANSWER is : Desity/ Molar mass = Molarity (UNDERSTANDABLE)

In other numerical
2. Concentration of H2SO4 is 98% by mass having density of 1.84gm/ml. Calculate Molarity.
here they used another formula.

now my question is, How second question is different from First ? why didnt they took density and devided it by Molar mass to get molarity?
What I am missing?
 
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  • #3
Sorry ! Corrected. It was missing decimal.
 
  • #4
I imagine the difference is in the concentration. If H2SO4 is 98% of the concentration by mass, is the 1.84gm/ml the density of H2SO4 or the density of the concentration?
Perhaps if you posted the formula you are looking at, it would make clear what the example is trying to show.
 
  • #5
Take as a basis 1 liter of solution. What is the mass of this 1 liter of solution? If the mass fraction of sulfuric acid is 0.98, what is the mass of sulfuric acid in the 1 liter of solution? How many moles is that?

Chet
 
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  • #6
Thank you guys for your reply.

Formula is MOLARITY = (%age * density *10)/ Density
 
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  • #7
Chestermiller said:
What is the mass of this 1 liter of solution? If the mass fraction of sulfuric acid is 0.98, what is the mass of sulfuric acid in the 1 liter of solution? How many moles is that?

Sorry I didnt get what you are implying.
Here is another way to Present my Doubt. We say that Molarity of Pure water is 55.5 ( which we calculate by using Density as 1)
Now By giving mass percentage, What extra information is given ?

SECOND: what is difference between STRENGTH of soln. and DENSITY of solution.
 
  • #8
Giving you what?
 
  • #9
Molarity

Well it is simple derivation, By considering mass of solution = 100gm and H2SO4 = 98gm
then they converted Mass of solution into VOLUME. and converted mass of H2SO4 into moles.
Once you have both of them, you can get molarity.

NOW my confusion is ... Why didnt they simply converted DENSITY ( gm/ml) Into Molarity ( MOLES/ ml)
what I am missing?
 
  • #10
Time to back up a couple steps; what is the definition of molarity?
 
  • #11
Moles in Litre Solution
 
  • #12
... and, if the density of 98% sulfuric acid is 1.84 g/cm3, one liter contains how many grams?
 
  • #13
I think I got it ?
If I only consider Density : 1 litres contain 1840 gm ,
Now this 1840gm will be of weight of (Sulphuric acid + water) ?
 
  • #14
harman90 said:
Now this 1840gm will be of weight of (Sulphuric acid + water) ?
Yes. How much sulfuric acid?
 
  • #15
Alright ...

SO 98gm H2SO4 in 100gm solution.
100 gm solution = 54.3 ml.

Weight of Sulphuric acid is = 98/54.3 * 1000 = 1804.8 gm
 
  • #16
Correct. That will be how many moles?
 
  • #17
18.4 moles

Thanks.
 
  • #18
This would all have been much simpler if you had chosen as a basis of the calculation 1 liter of solution rather than 100 gm of solution (as I suggested in post #5).
mass of 1 liter of solution = 1840 gm
mass of H2SO4 = (0.98)(1840)=1804.8 gm
moles of H2SO4 = 18.4
moles H2SO4 per liter of solution = 18.4

Chet
 

FAQ: Density of Solution and mass percent

1. What is density of solution?

Density of solution is the measure of how much mass is contained in a certain volume of a solution. It is usually expressed in units of grams per milliliter (g/mL) or grams per cubic centimeter (g/cm3).

2. How is density of solution calculated?

Density of solution is calculated by dividing the mass of the solute by the volume of the solution. The resulting value is then typically multiplied by 100 to express it as a percentage for easier comparison between solutions.

3. What is mass percent?

Mass percent is the percentage of the total mass of a solution that is made up of the solute. It is calculated by dividing the mass of the solute by the total mass of the solution and then multiplying by 100.

4. How is mass percent different from molarity?

Mass percent and molarity are two different ways of expressing the concentration of a solution. Mass percent is based on the total mass of the solution, while molarity is based on the number of moles of solute per liter of solution. They can be converted between each other using the density of the solution.

5. Why is it important to know the density and mass percent of a solution?

Knowing the density and mass percent of a solution is important for many reasons. It can help determine the physical properties and behavior of the solution, as well as the amount of solute present. It is also important for accurately preparing and diluting solutions in laboratory experiments and industrial processes.

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