One of the ingredients in the native american stomachache...

One of the ingredients in the Native American stomachache remedy derived from common chokecherry is caffeic acid (molar mass 180.16 g/mol). Combustion of 1.00 ×× 102 mg of caffeic acid yields 220 mg of CO2 and 40.3 mg of H2O. What is the empirical formula of this compound? List the elements starting with carbon, followed by hydrogen then oxygen. What is the molecular formula of caffeic acid? List the elements starting with carbon, followed by hydrogen then oxygen.

Transcript

00:01 Empirical formula is the simplest formula of a compound whereas molecular formula is the actual formula of the compound.

00:08 In this problem we have a compound that is composed of carbon hydrogen and oxygen.

00:15 This compound is cafeic acid, the molar mass of which is given to be equal to 180 .16 grams per month.

00:29 Now, this compound is made to react with oxygen via combustion reaction such that 1 times 10 to the power of 2 milligram of caffeine acid.

00:42 So, let's say, milligrams of the compound cho is 1 times 10 to the power of 2.

00:50 It is combusted with oxygen in air and the following masses of carbon dioxide and water, which are the products of combustion formed are as follows.

01:01 For milligrams of co2, it's 220, milligrams of h2o is 40 .3.

01:08 We want to establish the empirical as well as the molecular formula of the compound.

01:15 So let us start by taking note that by assuming that the combustion is complete so that all of the carbon turns into carbon dioxide and all of the hydrogen into water.

01:28 So let's find the minimals of co2.

01:32 Or rather see using the mass of co2 that is 220 so 220 mm.

01:40 So 220 milligrams of co2 divide this by the molar mass of co2 which is 44 .01 milligrams per millimole in order to convert it into millimoles and then using the relationship that 1 millimole of co2 will we will have 1 milamol of c and 8.

02:02 So solving this gives us a as 5 milimals which converts into milligrams of carbon by multiplying it by its own molar mass which is 21 .01 and this uh 12 .0 rather and this gives us 60 so 60 milligrams.

02:28 Next let's solve for the minimals of hydrogen using the amount of water that is formed which is 40 .3.

02:36 Divide this by the molar mass of water which is 18 .02 milligrams per millimole converts this into millimals of water and then using the relationship that one millimole of water contains two millimole of hydrogen you'll eventually get milimals of hydrogen and this solves into 4 .47 the milligrams of of hydrogen, we have 4 .47 times the molar mass of hydrogen, which is 1 .008.

03:16 And this gives us 4 .51.

03:24 So now the milligrams of the sample, cho, must be equal to the milligrams of the constituent elements it is made up with...

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