Dilution Calc: Find x for 30% Sulphuric Acid

Click For Summary

Discussion Overview

The discussion revolves around a homework problem involving the calculation of the mass of a 70% sulphuric acid solution needed to achieve a final mixture that is 30% sulphuric acid by mass when combined with a 20% sulphuric acid solution. The focus is on understanding the principles of mass percentage and conservation of mass in mixtures.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant states the problem and expresses uncertainty about using the equation a/b=c/d for the solution.
  • Another participant suggests using the equation C1V1 = C2V2, but acknowledges a lack of knowledge regarding moles or volume.
  • A different participant calculates the mass of sulphuric acid in the first solution as (150 * 0.20)g and mentions that water has a density of 1g/mL, implying a way to find volume.
  • Some participants argue that moles are unnecessary and emphasize using the definition of mass percentage and mass conservation instead.
  • One participant provides an example of mixing two different concentrations of sulphuric acid to illustrate the principles involved in the problem.
  • Another participant admits to misunderstanding the question and acknowledges that the C1V1=C2V2 approach is not applicable.

Areas of Agreement / Disagreement

There is no consensus on the best approach to solve the problem. Participants express differing opinions on whether to use molar calculations or focus solely on mass percentages and conservation principles.

Contextual Notes

Participants have not resolved the mathematical steps necessary to find the value of x, and there are varying assumptions about the relevance of moles and volume in this context.

triden
Messages
172
Reaction score
0

Homework Statement



150g of a solution which is 20% sulphuric acid (by mass) are added to x grams of a solution which is 70% sulphuric acid (by mass). What must be the value of x so that the final mixture shall contain 30% sulphuric acid (by mass)?

Homework Equations



a/b=c/d ? Not sure...this is my problem.

The Attempt at a Solution



I've tried equivalency calculation and any other ratio calculation that I could think of...all to no avail.

I know that 30g of the original solution is SA and 120g is water. So know I need to raise that concentration (mass SA to mass Water) by 10% with a 70% solution. Where do I get started?
 
Physics news on Phys.org
I would use C1V1 = C2V2

Where C = concentration in mols/L , and V = volume in Liters.
 
I don't know mols or volume. I think you can solve this question (somehow) without that knowledge.
 
Well the mass of the sulphuric acid for the first solution is (150 * 0.20)g wouldn't it?

So from there you can solve for mols.

Water has a density of 1g/1mL, so you have a volume.
 
This is nothing more than percentage and proportion. Your units are all by mass. (or grams, in this case).
 
No need for moles, and C1V1=C2V2 is not the correct approach.

All you need to use is definition of mass pecentage and mass conservation - whatever you add, it stays in the mix. If you mix two solutions, mass of water in the final solution will equal sum of masses of water in the input solutions. Same about sulfuric acid.
 
Borek said:
No need for moles, and C1V1=C2V2 is not the correct approach.

All you need to use is definition of mass pecentage and mass conservation - whatever you add, it stays in the mix. If you mix two solutions, mass of water in the final solution will equal sum of masses of water in the input solutions. Same about sulfuric acid.

Can you give me an example to get me started. It is probably way easier than it looks (to me).
 
Imagine you mix 100g 50% sulfuric acid with 50 g 20% sulfuric acid.

Using percentage definition, you get:

first solution: 50 g acid, 50 g water
second solution: 10 g acid, 40 g water
------------------------------------
mixture: 60 g acid, 90 g water

So the final solution is 40%.

You have to somehow reverse the problem, but the general approach will be based on the same principles.
 
Yeah I didn't read you question properly, C1V1= C2V2 will definitely not work.
 

Similar threads

  • · Replies 3 ·
Replies
3
Views
3K
Replies
3
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
3K
  • · Replies 0 ·
Replies
0
Views
2K
  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 4 ·
Replies
4
Views
39K