Learning ObjectiveTranslate in between a molecular formula of a compound and its percent composition by mass
Key PointsThe atomic composition of chemical compounds can be described in a selection of methods, including molecular formulas and percent composition.The percent complace of a compound is calculated with the molecular formula: divide the mass of each aspect discovered in one mole of the compound by the complete molar mass of the compound.The percent complace of a compound can be measured experimentally, and also these worths have the right to be used to determine the empirical formula of a compound.

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Termpercent by massThe fraction, by weight, of one aspect of a compound.

The atomic composition of chemical compounds deserve to be defined utilizing a selection of notations consisting of molecular, empirical, and also structural formulas. Anvarious other convenient way to define atomic complace is to examine the percent complace of a compound by mass.

Percent Composition by Mass

Percent composition is calculated from a molecular formula by splitting the mass of a single element in one mole of a compound by the mass of one mole of the whole compound. This worth is presented as a percentage.

Percentage Composition – YouTubeThis video reflects exactly how to calculate the percent composition of a compound.

For example, butane has a molecular formula of C4H10. Butane’s percent composition have the right to be calculated as follows:

Mass of H per mol butane: 10:mol:H cdot frac1.00794:g1:mol: H = 10.079:g:HMass of C per mol butane: 4:mol:Ccdotfrac12.011:g:C1:mol:C=48.044:g:CMass percent H in butane: frac10.079:g:H58.123:g:butane cdot 100 = 17.3% HMass percent C in butane: frac 48.044:g :C 58.123 :g :butane cdot 100 = 82.7% C

Thus, the atomic complace of butane deserve to additionally be described as 17.3% hydrogen and 82.7% carbon, and also, as meant, these worths amount to 100%.

*
ButaneThe structural formula of butane.

In exercise, this calculation is often reversed. Mass percents have the right to be figured out experimentally using elepsychological analysis, and these worths have the right to be offered to calculate the empirical formula of unrecognized compounds. However before, this information is inadequate to recognize the molecular formula without extra information on the compound’s molecular weight.

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