Chemistry - Mass Percentage

Problem Set


How do we express the concentration of a solute in a solution? We use Mass Percentage.

Mass Percentage is one of the way of representing the concentration of a solute in a solution. Mass percentage is calculated as the mass of a solvent divided by the total mass of the solution, multiplied by \(100\%\).

So it is easy to find out the formula:

\(\text{Mass Percentage }=\frac{m_{solute}}{m_{solution}}\times100\%\)

A \(200g\) beer contains \(20g\) alcohol. So, the mass percentage of alcohol in the beer is:

\(\frac{20g}{200g}\times100\%=10\%\).

Some other notes:

  1. The mass percentage does not change with the temperature and air pressure.

  2. There are other ways to express the concentration of a solute in a solution such as volume percentage, molality and amount-of substance concentration.

  3. Some reference books express mass percentage as \(g/g\). However, try not to use that to prevent a confusion with Solubility.

Now, there is an example:

I want to dilute a \(50g\), \(98\%\) \(H_2SO_4\) to a \(20\%\) solution. How much water should I add in grams to do this?

Solution:

\(50g\) is the mass of solution.

\(98\%\) is the mass percentage before adding water.

\(20\%\) is the mass percentage after adding water.

Note that the mass of \(H_2SO_4\) does not change before and after the water added.

So, let the fixed mass of \(H_2SO_4\) be \(c\) and the mass of water should add be \(x\)

Before adding water,

\(\frac{c g}{50g}\times100\%=98\%\)

\(c=\frac{98}{100}\times50\)

After adding water,

\(\frac{c g}{(50+x)g}\times100\%=20\%\)

\(c=\frac{20}{100}\times(50+x)\)

Compare the two equations we have,

\(\frac{98}{100}\times50=\frac{20}{100}\times(50+x)\)

\(x=195g\)

So, the amount of water we should add is \(195g\).

Note by Christopher Boo
4 years, 3 months ago

No vote yet
1 vote

  Easy Math Editor

MarkdownAppears as
*italics* or _italics_ italics
**bold** or __bold__ bold

- bulleted
- list

  • bulleted
  • list

1. numbered
2. list

  1. numbered
  2. list
Note: you must add a full line of space before and after lists for them to show up correctly
paragraph 1

paragraph 2

paragraph 1

paragraph 2

[example link](https://brilliant.org)example link
> This is a quote
This is a quote
    # I indented these lines
    # 4 spaces, and now they show
    # up as a code block.

    print "hello world"
# I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
MathAppears as
Remember to wrap math in \( ... \) or \[ ... \] to ensure proper formatting.
2 \times 3 \( 2 \times 3 \)
2^{34} \( 2^{34} \)
a_{i-1} \( a_{i-1} \)
\frac{2}{3} \( \frac{2}{3} \)
\sqrt{2} \( \sqrt{2} \)
\sum_{i=1}^3 \( \sum_{i=1}^3 \)
\sin \theta \( \sin \theta \)
\boxed{123} \( \boxed{123} \)

Comments

Sort by:

Top Newest

I can't find any good image for this topic. If you found one, feel free to give me the link! For your information, I will not continue any notes involve solution such as molality, ideal solution, Raoult's Law etc. because this topics need the concept of mol. So, I will continue to those section after the idea of mol is presented. However, I will continue my chemistry notes in gas.

Christopher Boo - 4 years, 3 months ago

Log in to reply

Thanks for this note...Could you also start a series on Organic Chemistry, if possible. Looking forward to your note on mole concept.

Anish Puthuraya - 4 years, 3 months ago

Log in to reply

Oops, sorry I can't start Organic Chemistry because I am weak in that part.

Christopher Boo - 4 years, 3 months ago

Log in to reply

What does \(20%\) solution mean?

Daniel Lim - 4 years, 2 months ago

Log in to reply

Sorry, it is 20%

Daniel Lim - 4 years, 2 months ago

Log in to reply

In this particular example, it means that the mass of \(H_2SO_4\) is \(20\)% of the mass of the solution.

Anish Puthuraya - 4 years, 2 months ago

Log in to reply

NICE POST!CAN YOU GIVE SOME NOTES ON EQUILIBRIUM.

Ojas Jain - 4 years, 3 months ago

Log in to reply

Ok but that may take some time, hope you can wait because now I am focusing on gases. :)

Christopher Boo - 4 years, 3 months ago

Log in to reply

×

Problem Loading...

Note Loading...

Set Loading...