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Daily Dose 043 | Chemistry
How to find the Mass Fraction?
Mass Fraction.
For most, this, amongst anything else Chemistry, isn’t a topic we easily accept as necessary knowledge in the world of engineering.
After all, we are trying to become Professional Engineers – not professional chemists, but…
We as engineers must understand the relationships between the structures and the properties of substances when specifying the materials within our designs.
Failing to do so can only increase the risks of catastrophic failure.
In this video, we dive into an FE Exam Practice Problem in the subject of CHEMISTRY, showing you how to quickly and efficiently solve these types of problems.
Key Definition
What is a MASS FRACTION?
A MASS FRACTION is a ratio that represents the mass of a particular substance in relation to the total mass of the mixture as a whole.
It can also be expressed, with a denominator of 100, as a percentage by mass (in commercial contexts often called percentage by weight, abbreviated wt%). It is one way of expressing the composition of a mixture in a dimensionless size, others being the MOLE FRACTION and the VOLUME FRACTION.
The Process
So how can we find the Mass Fraction?
Chemistry tends to present itself much more difficult than it actually is. In fact, most all problem types can be broken down into a general step by step process.
To find the Mass Fraction you can follow these general steps:
- Understand the problemRead the problem carefully and make sure you understand what is being asked. Identify the substances involved and any specific information provided.
- Determine the relevant massesIdentify the masses of the substances or components for which you need the fraction. If the masses are not directly given, you may need to use other information such as molar masses or stoichiometry to determine the masses.
- Calculate the total massDetermine the total mass of the system or mixture. This can be done by summing up the masses of all the components involved.
- Calculate the Mass FractionThe mass fraction of a component is the ratio of the mass of that component to the total mass of the system. With all the appropriate data defined, use the formula:
Mass fraction = (Mass of component) / (Total mass)
- Express the mass fractionIt is typically expressed as a decimal or a percentage. Depending on the problem or the requested format, convert the result to the appropriate form.
- Check the units and significant figuresEnsure that your calculations are consistent with the given units and any required significant figures. Round off the final answer as needed.
Worked Example
Let’s find a mass fraction
Say you dissolve 50 grams of salt into 150 grams of water. What’s the mass fraction of the salt?
- Mass of salt: 50 g
- Total mass: 50 + 150 = 200 g
- Mass fraction of salt: 50 / 200 = 0.25, or 25%
The water makes up the other 0.75 (75%), and the two always add to 1. That’s the whole calculation — the mass of the part over the mass of the whole.
Check out the video and see how we can go about solving this type of problem in the most efficient manner.
Video Review
[VIDEO] How to find the Mass Fraction
Next Step
What’s next?
Mass fraction has a sibling you’ll see just as often — the mole fraction — and the two trip people up precisely because they look alike. Lock down both and that whole family of problems gets easy.
Keep building — here’s how to solve mole fractions using the molar ratio — or let us build the plan around you.
We’ll assess where you stand, map a study plan to your timeline, and walk you through to exam day ready to pass. Seven days free, no credit card.
