Understanding how to get whole #s [ENDORSED]

[magaliolide1D]

So I'm very rusty with my high school chem. When I have finished getting the mols of a compound but have gotten 2.44 or something similar, should I round down or what would be the most logical thing to do?

[Maddie]

Is this for when you're finding the empirical formula or just converting grams to moles?

[PranaviKolla2B]

If you are solving from grams to mols, you can leave the number as is (2.44 mols is fine, you do not have to round). Hope this helps!

[Lara Kristine Bacasen 1L]

It depends on what you are trying to solve for. If you have a step beyond getting the moles you shouldn't round but if you don't then I would leave it as it is. I believe it is up to the person to decide if they want to leave it as is.

[Pipiena Malafu 3J]

Depends on the problem and significant figures but if it were 3 SFs then there shouldn't be a need to round down.

[Amy Kumar 1I]

For empirical formulas, if the value you got after dividing by the smallest number of moles was a decimal such as .25, .33, or .5, you would need to multiply all the molar quantities by the same number to make the decimal value a whole number.

[Areli C 1L]

From what I've been reading on the forums, our final answer should always be in the correct number of significant figures in order to be concise. So if the fewest number of sig figs in the problem was 4 then your final answer should contain only 4 sig figs.

[Jacob Villar 2C]

If you're trying to calculate the empirical formula, after finding the moles by converting from grams, divide by the smallest number of moles you received. Afterwards, if you end up with a mole amount of, say 2.5, you would multiply all the moles by an appropriate number to get to a whole number, in this case, to get to a whole number, you would multiply 2.5 by 2 to get to 5.

[Mariah]

If you are doing the empirical formula, I think that is when you have to worry about making things a whole number. Just remember you can manipulate numbers by multiplying, and dividing by the smallest if needed. Also whatever you do to one number, make sure to do to the others as well. If you fail to do this it can throw off the whole formula. Good luck!

[Tahlia Mullins]

The only time I usually round when calculating moles is when I am writing an empirical or molecular formula, because in a formula, there should not be any decimals/fractions. Although, when I am converting from grams to mols, I do round, at least to the correct number of significant figures.

[ClayMeunier1E]

You divide by the smallest number of moles at that point. If you don't have whole numbers after dividing once, start multiplying all of the numbers until all of them are whole. For example if you had 1.5 2 and 4, you would multiply them all by 2 to get 3, 4, and 8.

[Salma Fawzi 4G]

The empirical formula should not have fractions or decimals. You can manipulate the numbers by multiply by a number that will result in whole numbers in the formula only.

[Caitlin Ciardelli 3E]

2.44 is not close enough to round. If it was 2.98 I will usually round to 3 moles. When you divide by the smallest number and end up with a decimal answer, you will have to multiple every mole by whatever amount that will make that decimal a whole number. This is because we need whole moles as stochiometric coefficients.

[chrisleung-2J]

If you’re doing an empirical formula question and have already found the moles of each element in the compound, you must then divide each of the calculated mole values by the smallest mole value to get the ratio of each element to the others. After this, you must try to get whole numbers for the number of atoms of each element in the empirical formula for the compound by multiplying by the same number to get whole number values.

[Lauren Stack 1C]

If you are simply converting from grams to moles, or vice versa, having decimals is acceptable, as long as they go along with the rules of significant figures. In the case of 2.44, you have three significant figures listed.
If you are making an empirical formula, you should not have decimals for the moles. Thus, you must divide by the smallest value (of moles) that you have gotten from your percent composition calculations. From that, you should have numbers close to whole numbers, or a simple multiple such as 1.25, where you multiply all mole values by 4.

[Midori Hupfeld 3D]

If you're finding the empirical formula I think I would multiply 2.44 by 5 because it is not close enough to say it's 2.5 and just multiply by 2.

[Quynh Vo]

For this, you would need to multiply it by 2 to get a whole number. Rounding 2.5 either up and down is too much for the formula to have the same composition.

[EMurphy_2L]

In terms of finding an empirical formula, if you get moles being 2.1, round to 2. If you get 2.9, round to 3. A number like 2.44 is in the middle and shouldn't be rounded. You just multiply each number of moles by any number you want.
For example if you have 2.44 moles of one thing, 1 mole of another, and 5 moles of another, you could choose to multiply each by 2 so that you get approximately 5 moles, 2 moles, and 10 moles, respectively.
I hope I explained this somewhat clearly!

[gabbymaraziti]

Once you have calculated the moles of each element, you should first divide by the smallest number. If you still don't have integers for your answers, start multiplying through the numbers until you have whole integers.