Determine the empirical formulas for compounds with the following percent compositions: (a) 15.8

Determine the empirical formulas for compounds with the...

Key Concepts

Empirical Formula

An empirical formula represents the simplest whole-number ratio of the elements present in a compound. It provides insight into the basic composition of a substance by reducing the mole ratios of its constituent elements to their smallest integers.

Percent Composition

Percent composition refers to the percentage by mass of each element within a compound. It is used as the starting point in empirical formula calculations by assuming a convenient sample size, typically 100 grams, which converts the percentages directly into grams.

Conversion to Moles

Conversion to moles is crucial for empirical formula determination. By dividing the mass (in grams) of each element by its respective atomic mass, one calculates the number of moles of each element present, facilitating the comparison of the relative amounts of each element.

Normalization of Mole Ratios

Normalization of mole ratios is the process of dividing the number of moles of each element by the smallest number of moles calculated among them. This step simplifies the ratios to the smallest whole numbers, which are then expressed as the empirical formula.

Transcript

00:01 In this question, we've been asked to determine the empirical formula of the percent compositions of these samples.

00:11 So in order to determine the empirical formula, we need to first attain a ratio of the relevant compositions of these elements in the compound of interest.

00:26 So the first one is 15 .8 % of carbon and 84 .2 % of sulfur.

00:31 So in order to determine the empirical formula first we need to find this ratio and the ratio can be attained by taking the percentage of the element we have and dividing it by the molar mass because i was going to tell us the ratio of the element we have presents in the compound so for carbon which i'm going to indicate here by c right so we have 15 .8 % and we divide that by the molar mass which is 12 .011 this would give us a value of 1 .32 and on the other hand, for sulfur, we have 84 .2, divide that by the molar muscle sulfur, which is 32 .06.

01:20 This is going to give us a value of roughly 2 .63.

01:26 So given that now we have the respective ratios of these elements, we can now divide by the least amount, like the least ratio, and see the relative proportions of this respective elements.

01:44 So let's see we divide this by 1 .32.

01:47 This is going to give us a value of 1 roughly.

01:51 Divide this by 1 .32 as well.

01:55 This is approximately 2 .2 .2.

01:59 So it's like 1 .99, but it's pretty much 2.

02:03 So the percent composition of 15 .8 % carbon and 84 .2 % sulfur, that percent composition is going to give us an empirical formula of cs2.

02:22 So it means we have one carbon and two sulfur atoms.

02:26 So that's the empirical formula for the first one.

02:28 We do the same thing for the second part, which is part b.

02:33 Just like what we did, we're going to take 40 .0 divided by the molar mass of carbon 12 .011...