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University of New Mexico

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Problem 55

(a) Combustion analysis of toluene, a common organic solvent, gives 5.86 $\mathrm{mg}$ of $\mathrm{CO}_{2}$ and 1.37 $\mathrm{mg}$ of $\mathrm{H}_{2} \mathrm{O}$ . If the compound contains only carbon and hydrogen, what is its empirical formula? (b) Menthol, the substance can smell in mentholated cough drops, is composed of $\mathrm{C}, \mathrm{H},$ and $\mathrm{O} . \mathrm{A}$ 0.1005 -gsample of mentholis combusted, producing 0.2829 $\mathrm{g}$ of $\mathrm{CO}_{2}$ and 0.1159 $\mathrm{g}$ of $\mathrm{H}_{2} \mathrm{O} .$ What is the empirical formula for menthol? If menthol has a molar mass of 156 $\mathrm{g} / \mathrm{mol}$ what is its molecular formula?

Answer

a) $C_{7} H_{8}$

b) Final ratio is C 10 $\mathrm{H} 20 \mathrm{O}$ ; see explanation

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## Discussion

## Video Transcript

so to calculate the mass off carbon on hydrogen atom off the compound. As depicted, the mass off carbon turns out to be 1.5 98 into tender super negative three grams. When the mass off Hi, George Inness 1.53 into 10 days to part minus foreground. We need to deter mine the mole off each element. We know the formula to deter mined the number off moves us given beat divided by the molecular months. Using that formula, we can deter mined. There are 1.33 into 10 days to power minus four. Moves off carbon on 1.53 interchanges. Tobar minus four, moves off hydrogen carrying along to deter mined the simplest rule number ratio by dividing the each mold by this more less mole the smallest, the smallest more over here is off carbon 1.33 So we did. We divide each mole by this more, lest carbon turns out to be one and hydrogen turns out to be 1.15 Now the subscript off carbon is not a whole number. So we have to multiply both this subscript by the number which will provide us with the whole number. So carbon equals one multiplied by seven equals seven on hydrogen equals 1.155 multiplied with seven equals it. This give us an empirical formula off. Carbon and hydrogen is C 78 For their along, we need to calculate the mask off each element. The mass off carbon turned out to be 0.0 77 grounds while the Mars off hydrogen turns out to be 0.130 grams. No, we need to calculate the mass off oxygen so the mask off oxygen can be determined. Us. Let me show you. We just have to develop. Subtract the moss off carbon on the moss off hydrogen from the total mass off the sample. The total mass of the sample of zero point 100 five. Now we need to subtract 0.7 Last 0.0 13 for hydrogen, which gives us months off oxygen as 0.1 zero five rooms using the same formula as the previous one. We need to calculate the moon's off each element. The formula to deter mined the number off moons as vite divided by the molecular months. Using that formula. The Moors off carbon, hydrogen and oxygen has been determined for, though we need to determine the simplest wall number ratio by dividing each mole by the smallest mole, that is 6.56 to 5 into 10 days to buy. Negative for more. Doing so, we have carbon astin hydrogen as 20 excision as one, which gives us a new empirical formula for see 10. It's starting on oxygen deter. Minding the mal de molecular mass or the empirical formula Mars off. This is carbon. The mask is 12 so we multiply 10 with will hydrogen masses one as their 20 atoms multiplied with 20 oxygen, only one Adam having mass off 16 adding, these we have the total mass equals 156.2 rounds. Finally, we need to determine the molecular formula for the company. We're an equals Moeller must divided by empirical must. It gives us 100 and 56 divided by 156.2. It gives us theatre 0.99 almost equally, willinto one, So the model glue formula will be the same as a baker formula. See 10. It's 20 oxygen

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