A gaseous compound containing hydrogen and carbon is decomposed and found to contain 82.66 % car

A gaseous compound containing hydrogen and carbon is...

Key Concepts

Molar Mass Calculation

Molar mass is the mass of one mole of a substance and is calculated by dividing the mass of the sample by the number of moles present. This concept is important when connecting experimental measurements with molecular formulas, especially in the context of determining the relationship between the empirical formula mass and the molecular formula mass.

Percent Composition

Percent composition refers to the percentage by mass of each element in a compound. It is a fundamental concept in chemical analysis that allows one to determine the relative amounts of each element present in a compound. This information is critical for deducing the empirical and ultimately the molecular formulas of unknown compounds.

Empirical Formula Determination

The empirical formula of a compound represents the simplest whole-number ratio of atoms of each element in the substance. It is determined by converting the percent composition into moles, finding the ratio of moles for all elements, and then reducing these ratios to the smallest whole numbers. This process is essential in the stoichiometric analysis of compounds.

Molecular Formula Determination

The molecular formula indicates the actual number of atoms of each element in a molecule and is a multiple of the empirical formula. Once the empirical formula mass is known, the molecular mass of the compound (often determined from experimental measurements) can be used to determine the multiple factor that relates the empirical formula to the molecular formula.

Ideal Gas Law

The Ideal Gas Law (PV = nRT) relates the pressure (P), volume (V), number of moles (n), temperature (T), and the gas constant (R) for an ideal gas. It is used to calculate the number of moles in a gaseous sample when the conditions of pressure, volume, and temperature are known, thereby linking macroscopic measurements with molecular quantities.

Transcript

00:04 In this question, we have a gaseous compound containing hydrogen and carbon, and we're told that it contains 82 .66 % carbon and 17 .34 % hydrogen by mass.

00:17 They tell us that the gas has a volume of 158 milliliters, a mass of 0 .275 grams, a pressure of 556 millimeters of mercury, and a temperature of 25 degrees celsius, and they ask us to find the molecular formula of the compound.

00:35 So the first thing i'm going to do is convert all of these numbers that they've given me into units that i can use in the ideal gas equation because we're going to use that a little bit later.

00:47 So my volume needs to be in liters.

00:49 So to get from milliliters to liters, i divide by a thousand and i get 0 .158 liters.

00:56 My temperature needs to be in kelvin.

00:58 So to get from celsius to kelvin, you just add 273.

01:02 So i'll have a temperature of 2 .5 .8 liters.

01:04 So i'll have a temperature of 2 .5.

01:04 298 kelvin and my pressure needs to be in atmospheres.

01:09 So to get from millimeters of mercury to atmospheres, you divide by 760 and i will get 0 .732 atmospheres.

01:20 Now what i'm going to do next is use all these quantities and the ideal gas equation, which is pv equals nrt to find n.

01:31 So n is the number of moles.

01:33 That's what we're going to look for and figure out how many moles of gas are in our present here.

01:40 And then we will use that number to figure out the molecular formula.

01:49 So this is the ideal gas equation.

01:51 P is pressure, v is volume, n is a number of moles, r is a constant, and t is temperature.

01:57 So if i plug all these values that i have in, my pressure is zero.

02:02 0 .732 atmospheres.

02:05 My volume is 0 .158 liters.

02:08 We're looking for n...

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