Converting from grams to percentage

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romina_4C
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Converting from grams to percentage

Postby romina_4C » Thu Oct 10, 2019 3:14 pm

In class when we completed the Vitamin C problem, I remember that we converted the grams of each element into percentage using the total grams of vitamin c. In other problems (such as F13), it is not required to convert to percentage to do the problem. I guess my question is when do we have to convert to percentage to find the empirical formula and when do we just use the grams (and convert to moles) that they give us?

Paige Lee 1A
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Re: Converting from grams to percentage

Postby Paige Lee 1A » Thu Oct 10, 2019 3:19 pm

When you convert to a percentage, you assume a 100g sample, and then convert to moles. Using moles, compare the various elements to find their ratios to each other. Using this information, you can find the empirical formula. If the question specifies for an answer in grams, you may need to take a few further steps to convert the amount of a substance from moles to grams.

Zaynab Hashm 2I
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Re: Converting from grams to percentage

Postby Zaynab Hashm 2I » Thu Oct 10, 2019 3:21 pm

When it is already given in a percentage (of a hundred), we assume it is a 100g sample and use the numbers as they are given. But when you are given a sample of a different mass that is not 100g total, then you have to convert the individual masses by finding their mass percent composition for easier calculations.

Jarrett Peyrefitte 2K
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Re: Converting from grams to percentage

Postby Jarrett Peyrefitte 2K » Thu Oct 10, 2019 3:24 pm

To find the empirical formula, you should always turn the percentage values given to you and imagine the sample mass is 100g (Ex. 54.5% --> 54.5 grams) . Then divide by the molar mass, and divide by the smallest value (molecule must have whole atoms) .

Haley Chun 4H
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Re: Converting from grams to percentage

Postby Haley Chun 4H » Thu Oct 10, 2019 3:30 pm

When you are given the grams of each element in the problem, I don't think it is necessary to find the %mass composition because you can just convert to moles right away and find the mole ratio (goal). I believe you only need to use the 100 gram sample when the problem gives the % composition only (so you can find moles)

Jasmine Summers 4G
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Re: Converting from grams to percentage

Postby Jasmine Summers 4G » Thu Oct 10, 2019 3:52 pm

Assuming you have a 100g sample is the easiest way to do it because you bypass finding mass percentage composition and equate the given percentages to mass. You then use those masses to find moles.

Juana Abana 1G
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Re: Converting from grams to percentage

Postby Juana Abana 1G » Fri Oct 11, 2019 2:30 pm

In order to find the empirical formula, you should first turn the grams given into a percentage. Then divide by the molar mass, and then divide by the smallest value.

Jainam Shah 4I
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Joined: Fri Aug 30, 2019 12:16 am

Re: Converting from grams to percentage

Postby Jainam Shah 4I » Fri Oct 11, 2019 2:37 pm

We converted the grams into percentage in the Vitamin C problem because we were simply given grams of each element and the final compound. To find an empirical formula it comes down to obtaining the mass percentage composition. In the Vitamin C problem we found molar mass each element and divided it by the the molar mass of the compound formed to find the percentage composition of each element. From there we could find moles of each element and find the molar ratios. In other problems we do not covert grams to percentages, because we are already given the percentage composition of each element in the compound. We can assume a 100g sample because it makes it convenient to convert the percentages to grams directly. Then we do the same thing by converting to moles and finding the molar ratios between the elements.

Viviana Velasquez
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Joined: Sat Jul 20, 2019 12:15 am

Re: Converting from grams to percentage

Postby Viviana Velasquez » Sun Oct 13, 2019 3:52 pm

You should convert the grams to a percentage when you are given the amount of grams of each element and the total mass of the compound to find the mass percentage composition. Then assuming you have 100 g, you would convert the percentage to grams and then moles. Sometimes the mass percentage composition will be given and you will only need to convert to grams and moles.

Kaitlynn Tran 3F
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Joined: Wed Sep 18, 2019 12:20 am

Re: Converting from grams to percentage

Postby Kaitlynn Tran 3F » Sun Oct 13, 2019 10:48 pm

If you are given a percentage in a problem, it is easy to imagine that you have a total of 100g. So theoretically, if you have 16% C, you can assume there are 16g C. With the amount in grams, you can convert to moles to find the ratio for empirical formula.

Caitlin Ciardelli 3E
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Joined: Wed Sep 18, 2019 12:19 am

Re: Converting from grams to percentage

Postby Caitlin Ciardelli 3E » Sun Oct 13, 2019 11:07 pm

Empirical formulas show the ratio of each element in relation to the other elements. To find this, you need to compare their molar amounts. To find molar amounts, you need the grams. If the mass in grams is not provided, we can use the percentages and assume that the mass is 100 g. I find that when I think backwards like this, it helps me to understand when to use percentage and when not to. If grams is provided, you do not need to convert the percentages.

- convert percentage >> grams >> moles (when grams is not provided)
- convert grams >>> moles (when grams are provided)

Annika Zhang 1F
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Joined: Sat Jul 20, 2019 12:15 am

Re: Converting from grams to percentage

Postby Annika Zhang 1F » Sun Oct 13, 2019 11:12 pm

when finding the empirical formulas, percentages are usually given for each element's make up in the compound. Thus, when we are given only the percentage without a specific mass of the sample, we assume that there is a 100g sample. This allows you to covert percentage directly to it's same numerical value in mass (45% C=45g C). From there, you can convert grams to mols using molar mass, making it much easier than assuming another mass for the sample.


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