Percent comp calculations
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Percent comp calculations
How do you find percent comp by mass of each element when given only the molecular formula?
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Re: Percent comp calculations
The molecular formula is the actual number of each element in the molecule.
Add up the mass of each element in the molecule to find the total mass.
Then you take the total mass for each individual element, divide by total mass then multiply by 100 to get the mass percentage for each element.
Add up the mass of each element in the molecule to find the total mass.
Then you take the total mass for each individual element, divide by total mass then multiply by 100 to get the mass percentage for each element.
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Re: Percent comp calculations
Seems like the explanation was given already but as an example, with butane C4H10, you would first find the total mass using the molar mass of each element in it: 4(12.01)+10(1.01) = 58.14 grams (because the molar mass of carbon is 12.01 g/mol and the molar mass of Hydrogen is 1.01 g/mol).
Then take the mass of each element, so for carbon in this case it would be 4(12.01)= 48.04 g, and then divide it by the total mass and multiply it by 100%. (48.04/58.14 g)*100% = 82.63 % Carbon. Repeat with the other elements!
Then take the mass of each element, so for carbon in this case it would be 4(12.01)= 48.04 g, and then divide it by the total mass and multiply it by 100%. (48.04/58.14 g)*100% = 82.63 % Carbon. Repeat with the other elements!
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Re: Percent comp calculations
To answer your question,
Percent mass composition can be found with just the molecular formula. For each element in the molecular formula, you can do the following:
(molar mass of element) * (# of moles of the element in the formula) / (total molar mass of the substance)
NOTE: make sure to multiply by 100 to get percent
If you wanted to know a specific quantity of an element in a compound based on the percentages, you would just take the percent you found and multiply it by the mass of the compound in question.
Percent mass composition can be found with just the molecular formula. For each element in the molecular formula, you can do the following:
(molar mass of element) * (# of moles of the element in the formula) / (total molar mass of the substance)
NOTE: make sure to multiply by 100 to get percent
If you wanted to know a specific quantity of an element in a compound based on the percentages, you would just take the percent you found and multiply it by the mass of the compound in question.
Last edited by Sami Siddiqui 1J on Mon Oct 05, 2020 3:57 pm, edited 1 time in total.
Re: Percent comp calculations
Hi!
You can always find the mass percentage composition by the mass of each element then dividing the mass of the entire molecule and multiplying it by 100.
E.g. Find the mass percentage composition of C,H, O, from C6H12O6.
Let's find the mass of the the entire glucose molecule (C6H12O6)
1. You calculate the mass of 6 C atoms which is (12.011 x 6 ) = 72.066 g/mol.
2. You calculate the mass of 12 H atoms which is (1.008 x 12 ) = 12.095 g/mol.
3. You calculate the mass of 6 O atoms which is (15.999 x 6 ) = 95.994 g/mol.
4. Add all of the calculated mass (72.066 g/mol + 12.095 g/mol + 95.994 g/mol) = 180.156 g/mol.
5. To find the mass percentage composition of C divide 180.156 g/mol from 72.066 g/mol (72.066 / 180.156 = 0.400) and multiply by 100 to get 40.0% or 40.0g C.
6. Repeat step 5 but for H and O.
Note: To get the empirical formula, simply find the ratio of the elements. The empirical formula from glucose (C6H12O6) is CH2O a 1:2:1 ratio.
Hope this helps!
You can always find the mass percentage composition by the mass of each element then dividing the mass of the entire molecule and multiplying it by 100.
E.g. Find the mass percentage composition of C,H, O, from C6H12O6.
Let's find the mass of the the entire glucose molecule (C6H12O6)
1. You calculate the mass of 6 C atoms which is (12.011 x 6 ) = 72.066 g/mol.
2. You calculate the mass of 12 H atoms which is (1.008 x 12 ) = 12.095 g/mol.
3. You calculate the mass of 6 O atoms which is (15.999 x 6 ) = 95.994 g/mol.
4. Add all of the calculated mass (72.066 g/mol + 12.095 g/mol + 95.994 g/mol) = 180.156 g/mol.
5. To find the mass percentage composition of C divide 180.156 g/mol from 72.066 g/mol (72.066 / 180.156 = 0.400) and multiply by 100 to get 40.0% or 40.0g C.
6. Repeat step 5 but for H and O.
Note: To get the empirical formula, simply find the ratio of the elements. The empirical formula from glucose (C6H12O6) is CH2O a 1:2:1 ratio.
Hope this helps!
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Re: Percent comp calculations
To reiterate what others have posted above, when given the molecular formula your first step is to find the molar mass. Once you have the total more mass, you can find the molar mass of each individual atom and divide that by the total and multiply by 100% to get the mass percent composition!
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