A gaseous hydrogen- and carbon-containing compound is...

A gaseous hydrogen- and carbon-containing compound is decomposed and found to contain $85.63 \% \mathrm{C}$ and $14.37 \% \mathrm{H}$ by mass. The mass of $258 \mathrm{~mL}$ of the gas, measured at STP, was $0.646 \mathrm{~g}$. What is the molecular formula of the compound?

Key Concepts

Percent Composition

Percent composition represents the proportion by mass of each element in a compound. It is used to determine the relative number of moles of each element present in a sample by converting the mass percentages to mass, and then to moles using their atomic masses.

Empirical Formula Determination

Empirical formula determination involves converting the percent composition into moles for each element and then finding the simplest whole-number ratio. This ratio provides the basic 'recipe' for the compound, showing the lowest number of atoms of each element present.

Gas Laws and Molar Volume at STP

At standard temperature and pressure (STP), gases are known to occupy a fixed molar volume. This concept is crucial for converting a given volume of gas to the number of moles, which ties together the observed physical properties (like density) with chemical composition.

Molecular Formula Determination

Once the empirical formula is known, the molecular formula is determined by comparing the mass of the empirical formula unit to the actual molar mass of the compound. This involves calculating the empirical formula mass and using additional data, such as the density or measured gas volume, to find the multiple that relates the empirical formula to the actual molecular structure.

Transcript

00:01 Explanation for the question here here we have to find molecular formula by using the given data so here we have given data is we have elements here given elements are carbon and hydrogen and next is percentage composition of carbon in hydrogen and then we have here we have to find number of grams items.

01:24 After date, you will find atomic ratio.

01:34 And finally, we'll find empirical formula.

02:11 So here elements, first element is carbon.

02:18 And carbon percentage composition is here, 85 .63 gram of carbon.

02:32 And next is hydrogen.

02:40 And percentage composition of hydrogen is 14.

02:44 37 gram hydrogen.

02:47 Now we will find number of gram atoms.

02:50 So here the formula is given mass divided by molar mass.

02:57 So here given mass is 85 .6363 divided by 663, multiplied 1 mole of carbon divided by 12 .010.

03:28 7 gram of carbon so here is also gram of carbon so this board unit will cancel and remaining unit here is small is equal to we have here 7 .1 2995 mall of carbon and next is here given mass is 14 .37 gram of hydrogen into 1 molar hydrogen divided by 1 .0079 gram of hydrogen.

04:25 This can sell with this one and is equal to we have here 14 .257 more molar hydrogen.

05:05 And here next we have atomic ratio.

05:16 To find atomic ratio we will divide by summa's number of moles.

05:22 So here 7 .125 mole of carbon divided by sumal's number of mall is 7 .125 mole is equal to we have one carbon atom.

05:53 And next is 14 .25...

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