Conine, a toxic substance isolated from poison hemlock, contains only carbon, hydrogen, and nitr

Conine, a toxic substance isolated from poison hemlock,...

Key Concepts

Determining Nitrogen Content by Difference

In compounds containing nitrogen, the nitrogen content is often not directly measured through combustion products like CO2 and H2O. Instead, the mass attributable to nitrogen is determined by subtracting the masses of carbon and hydrogen (derived from their corresponding combustion products) from the original sample mass. This remaining mass is then converted into moles to be used in the empirical formula calculation.

Combustion Analysis

Combustion analysis is a method used to determine the elemental composition of organic compounds by burning them to produce measurable amounts of products such as carbon dioxide and water. The masses of these products provide information about the amounts of carbon and hydrogen present, which is critical for determining the compound’s overall composition.

Empirical Formula Determination

Empirical formula determination involves converting the masses of elements into moles and then identifying the simplest whole-number ratio among these moles. This technique is used to derive a formula that represents the relative number of atoms of each element within the compound.

Conversion of Combustion Products to Elemental Composition

This concept involves calculating the moles of carbon from the mass of CO2 and the moles of hydrogen from the mass of H2O produced by combustion. These calculations require the use of molecular weights and the known composition of the combustion products, forming the basis for deducing the elemental makeup of the original sample.

Transcript

00:02 We're going to start by finding how many milligrams, excuse me, moles of carbon are in these many milligrams of co2.

00:11 First, we're going to make sure that we're working in grams.

00:15 To change milligrams to grams, we're going to divide by 1 ,000.

00:18 So this is 0 .0 -1390 grams of co2.

00:25 I want my goal right now is to find moles of co2 first.

00:29 So i'm going to divide by the molar mass.

00:32 That's 44 .01 grams of co2 in every one mole of co2.

00:39 For completeness i'm going to go ahead and multiply by the 1 to 1 mole ratio, one mole of carbon in every 1 mole of co2.

00:48 Notice that my units cancel and this helps me identify that there are 0 .003158 moles of carbon present in the sample i'm going to repeat the same process for water.

01:12 My goal is to find how many moles of hydrogen, not how many moles of water there are.

01:17 So same idea, divide first by 1 ,000 to get from milligrams to grams.

01:22 This is 0 .006 -48 grams of water.

01:34 Molar mass of water, one mole of h2o contains 18 .02 grams of h2o.

01:43 This mole ratio is relevant.

01:46 There are two moles of hydrogen in every one mole of water.

01:54 So multiplying through, i find that this sample contains 0 .0060 -61713 moles of hydrogen.

02:08 Now if this compound contain nothing but carbon and hydrogen, i would be able to write a chemical formula using just carbon and hydrogen, but we know from the problem that this sample also contains nitrogen.

02:25 To find how much nitrogen there is, i need to figure out what the mass of these two elements is and subtract it from the total mass of the compound which contains nitrogen.

02:37 So to do that, i'm going to take an extra step and divide each, multiply each of these, by the molar mass of each element to find that there are 0 .00379 3 grams of carbon or 3 .979 milligrams of carbon...

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