What are the empirical formulas of the compounds with the following compositions? (a) 2.1 percen

What are the empirical formulas of the compounds with the...

Key Concepts

Mole Ratio Determination

Once the number of moles for each element is found, the next step is to divide all mole amounts by the smallest number of moles present. This process yields the simplest whole-number ratio of the elements, which is necessary for writing the empirical formula.

Empirical Formula

The empirical formula represents the simplest whole-number ratio of the elements in a compound. It is derived from the mole ratio of the constituent elements and provides important information about the compound's composition and stoichiometry.

Percent Composition

Percent composition is the percentage by mass of each constituent element in a compound. It is used to determine the relative amounts of each element present, which is essential when converting these percentages into moles for empirical formula determination.

Conversion to Moles

This concept involves converting the mass or percentage of each element in a compound to moles by using the element's molar mass. This step establishes the number of moles for each element and forms the basis for finding the simplest ratio of atoms in the compound.

Transcript

00:02 So for this problem, we're trying to determine the empirical formula of two different compounds.

00:08 So looking at this first compound, we have the percent composition of the elements, hydrogen, oxygen, and sulfur that make up this first compound.

00:19 So first thing we can do in calculating the empirical compound is consider if we have 100 grams of compound, then that's a way of us to determine how many grams do we have of each of these individual elements in the 100 grams of compound.

00:51 So 2 .1 % of 100 is 2 .1 grams and then so on.

00:58 The reason we approximate we use 100 grams instead of one gram or another amount is because 100 grams makes the math easier for this step.

01:12 So now for determining the empirical formula, eventually in our last step, we want to go to compare mole ratios.

01:21 So we need to know how many moles of each of each of these elements there are.

01:27 So starting with hydrogen, we'll take the 2 .1 grams divided by its molecular weight and do the same for oxygen, divided by 16 grams per mole.

01:51 And sulfur.

02:00 We're going to divide that by it's molecular weight of 32 .7 grams per mole.

02:08 So now if i get my calculator, this will be 2 .08 moles, 4 .08 moles, and 1 .02 moles.

02:41 So the next thing for determining the mole ratios is to determine rich of these moles is in the lowest quantity.

02:50 So for this compound, that's sulfur.

02:56 And you'll notice that the reason we have, and now it becomes more apparent why we had to convert to moles, because you'll see once we do conversion to moles, we see that sulfur is present in the least amount.

03:08 But if we're going based on percent compositions alone, we would not see that trend.

03:13 Based on the percent compositions, hydrogen appears to be in the smallest amount.

03:17 But it only seems that we're going.

03:20 Way because its molecular weight is so small.

03:23 So that's why it's important to calculate through using its molar mass.

03:30 So what we do now is to do the mole ratios.

03:34 We're going to divide each of these moles by the number of moles of sulfur.

03:42 So i'm going to switch back to green here.

03:44 So we'll take the number of moles of hydrogen divided by 1 .02 mole of sulfur.

03:54 And that's going to be equal to about two.

03:59 Then we're going to divide the number of moles of oxygen by the number of moles of sulfur, and that'll be equal to about four.

04:08 And then we divide, if we divide the number of moles of sulfur by itself, then it's going to equal to not even about one.

04:18 It will be equal to one...

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