Salicylic acid, used in the manufacture of aspirin, contains...

Salicylic acid, used in the manufacture of aspirin, contains only the elements $\mathrm{C}, \mathrm{H},$ and $\mathrm{O}$ and has only one acidic hydrogen that reacts with NaOH. When 1.00 $\mathrm{g}$ of salicylic acid undergoes complete combustion, 2.23 $\mathrm{g} \mathrm{CO}_{2}$ and 0.39 $\mathrm{g} \mathrm{H}_{2} \mathrm{O}$ are obtained. When 1.00 $\mathrm{g}$ of salicylic acid is titrated with $0.100 \mathrm{M} \mathrm{NaOH}, 72.4 \mathrm{mL}$ of base is needed for complete reaction. What are the empirical and molecular formulas of salicylic acid?

Key Concepts

Acid-Base Titration

Acid-base titration is an analytical technique used to determine the quantity of a specific acid or base in a solution by reacting it with a titrant of known concentration. In the context of organic compounds with acidic functional groups, titration data can be used to confirm the number of acidic protons present.

Molecular Formula Determination

Molecular formula determination involves using the empirical formula along with additional information such as the compound’s molar mass to find the actual number of atoms in a molecule. This step scales up the empirical formula to reflect the true composition of the compound.

Empirical Formula Determination

Empirical formula determination uses the relative amounts of the elements, derived from combustion analysis, to establish the simplest whole-number ratio of atoms in a compound. This step provides the basic formula without indicating the actual number of atoms in the molecule.

Combustion Analysis

Combustion analysis is an experimental technique that involves burning a compound and measuring the masses of the resulting products (usually carbon dioxide and water) to determine the amounts of carbon and hydrogen present. This data allows for the calculation of the elemental composition of the compound.

Transcript

00:04 Let's determine the empirical and molecular formulas of salicylic acid.

00:09 First of all, let's calculate the molar mass using the information given.

00:14 So we have 72 .4 milliliters of 0 .1 molar n -a -o -h.

00:23 So let's convert this to moles.

00:29 So moles of n -a -o -h would be equal to the malaria.

00:36 Times the volume in liters, this would be equal to .00724 moles.

00:48 And the mass of n -a -o -h would be equal to .00724 moles times the molar mass, 1 mole of n -a -o -h is 40 .0 grams.

01:02 So this would yield 02896 grams of n -a -o -h.

01:13 So we're told that 0 .2896 grams of n .a .o .h will neutralize, neutralizes one gram of the salicylic acid.

01:34 And so 40 grams neutralizes, so 40 grams of n .ao .h will neutralize.

02:16 Neutralizes 40 over 0 .2896 and this would be equal to 138 grams of the salicylic acid.

02:41 So this is our molar mass here.

02:45 Next part of this, in one gram of so the amount of carbon.

02:54 So the amount of carbon, in 1 gram salicylic acid.

03:05 We're told that we've got 2 .23 grams of co2, 44 .0 grams of co2 to 12 grams of carbon, and this would work out to 0 .608 grams of carbon.

03:23 And the percent carbon is 0 .608 grams carbon over the one gram of the acid times 100 percent, and this would work out to 60 .8 percent carbon.

03:44 Let's now calculate the amounts of hydrogen in one gram of salicylic acid, and we're told that we have 0 .39 grams of water, 18 .0 grams, 2 .0 grams of hydrogen...

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