Empirical Formula

[Sofia Cerpa 2E]

when calculating the empirical and molecular formulas, is it always assumed that the sample mass is 100g?

[Chloe Borja 2D]

I think you're referring to when we're given the mass percent composition (e.g. a compound is 25% O). In that case, just to make it easier, we would use 25g of O. However, we would assume the sample is 100g because we were given the percentage; in other situations where we might be given the actual amount in grams, for example, you would just need to be careful. Hope that helps!

[Abhinav Amanaganti 3K]

You should assume 100g if you are not given an exact molar mass for simplicity (also 100g should be assumed for percent composition problems for simplicity too), but when given a molar mass, calculate the empirical formula using the given value.

[Ellie Fox 2K]

Yes technically you can use whatever value you want as sample mass as long as they are proportional to the mass percent given. We just use 100g as the sample because when given percent composition it's simplest to just be able to use those same numbers instead of converting.

[Diego Gonzalez 1H]

When we are working with mass percentages (mass percent composition) we often use 100g as the standard because it has a 1:1 ratio with percentages, making it simpler to work with.

[Sevde Coban 2J]

Using 100g makes it easier to get the mass of the elements, especially if the mass percent composition is given. But you could use any mass as long as you convert the percentages accordingly.

[Sonia Virk 2A]

If there is no mass for the sample but there is the mass percentage composition, then yes it is most convenient to assume the sample is 100g so it is easy to convert the percentage into grams. Hope this helps!

[PatrickV]

You do not need to assume that it is 100g, but it is definitely the easiest because it takes some calculations out because if you are multiplying a percentage by 100, all you need to do is move the decimal place twice.

[505784197]

The 100g is just needed when transitioning the percentages to grams of each atom in the molecule.

[Ameerah Hameed 3B]

Assuming the sample mass to be 100 grams is best when not given the exact mass because it makes the process of mass percent composition easier due to the fact that it has a 1:1 ratio which allows you to skip additional converting.

[Iman Gauhar 3E]

Hi! When finding the empirical formula, it is usually easier to just assume that each percent value is out of 100%. For example, x = 30% can be converted to x = 30 grams if you do not know the exact molar mass of the compound.

[Jamie Lau 2J]

You don't have to use 100g, but it makes it easier to calculate mass from percentages given.

[Aashna Sibal 2F]

Usually, in the problems, a percentage is given, for example 30%. Since percentages are out of 100, it's easier to do the calculations pretending the sample is 100g, so you can assign the element that is 30% of it to be 30 g.

[Eszter Kovacs 1A]

You can use different methods to determine the empirical formula but assuming that you have 100g of a compound is the easiest when it comes to calculating percentages.

[Katryn Heine 3A]

Yes. It's the easiest way to find the percent composition for each element in the molecule.

[Brooklyn Burgess 3L]

How do we find the mass percent composition when we only know the empirical formula and nothing else?

[Ellen Brock 2I]

Yes, usually 100g will be used if it is not explicitly said what the actual mass was. It also has to do with percentages of each of the compounds adding up to 100. But if we are actually given a mass then use that or else you will not get the correct answer

[bernal_maria1A]

When finding the empirical formula, if you are given mass percentages you can use 100g. For example, there 13.13% of H in the formula C2H6O, a way to solve for the empirical formula would be to convert 13.13% to 13.13g of 100g. You would go from there and convert to moles.

[Coraly De Leon]

Yes, its very helpful to use 100 g if the actual mass isn't given.

[Brianna Mercado 3D]

Hi! You should only assume 100g if you are not given the exact molar mass

[Maia Holmes Kueny 1C]

Unless the mass is given, yes.

[405996618]

That assumption is used by us, or a person showing us their solution just to make the solving process look simpler or easier. We assume it to be 100g for us to be able to write for example 4.5g, instead of using percentages like 4.5%. This will just get the units portion of the solution to look simpler and avoid mistakes.