Avobenzone is a common ingredient in sunscreen. Its structural...

Question

Avobenzone is a common ingredient in sunscreen. Its structural formula is shown.

b. What is the molecular formula and molar mass of avobenzone?

Accepted Answer

All right. Hello everyone. So this question says that the structural formula for phenox ethanol is shown below. It is used as a preservative in cosmetic products give its molecular formula and molar mass. And here we have four different answer choices labeled A through D proposing different molecular formulas and different molar masses. So first, I want to go ahead and actually find the molecular formula of the compound because recall that the molecular formula lists all elements present in the compound as well as how many there are in the compound itself. This is going to be very useful to us when calculating the molar mass. So to understand the molecular formula that we're going to be finding what I want to point out here is that this compound is shown to us with a skeletal formula or a line structure. And what I mean by this is that carbon atoms are not actually drawn in the structure. Instead, corners and open ends are implied to be carbon atoms. Now, hydrogen atoms that are attached to carbon atoms are not drawn either instead they are implied to be present. And so every carbon atom present in this molecule is implied to have enough hydrogen atoms to fulfill carbon's four bond requirement. Whereas other elements like nitrogen, oxygen and any halogens are always shown. But in this case, the carbons in the ring structure that do not have other substituents are each implied to have one hydrogen atom to fulfill carbon's four bond requirement. So I am going to draw them just to make counting them easier. So if I consider the two carbons from ethanol, both of those would be implied to have two hydrogens because each of them already have two bonds to other atoms. So with this in mind, we can go ahead and count all atoms present in this compound of which I have three types, I have carbon hydrogen and oxygen. So in this case, I'm going to start with a number of carbon when it comes to the number of carbons, I have six from the benzene ring and an additional two from ethanol giving me a total of eight. Whereas for hydrogens, I have five hydrogens from the benzene ring and an additional four from ethanol. But notice how I also have a hydrogen atom attached to oxygen. So that would count as one more, which gives me a total of 10 hydrogens in this compound because recall that hydrogens attached to atoms other than carbon are always going to be shown in a skeletal structure. And as for oxygens in the structure here, we can see that we have two, one from the O group and the other from the Foxy group. So when I put everything together in my molecular formula, the quantity of each atom is written as a subscript. So that's C eight H 10 02. So at this point, I can go ahead and proceed with the molecular formula or excuse me, the molar mass, I already have the molecular formula. But recall that the molar mass refers to the cumulative mass of a given compound. It is the total mass of all atoms present in the molecule. So to calculate the molar mass of phenoxyethanol, I'm going to first recall the molar masses of each constituent element according to the periodic table. Recall that the molar mass of carbon is 12.01 g per month. For hydrogen, it is 1.008 g per mole. And for oxygen, it is 16.00 g per mole. So what I'm going to do here is I'm going to take the molar mass of each individual atom and multiply them by the quantity of each atom according to my molecular formula. So starting off with the molar mass of carbon, I would take the molar mass of carbon and multiply this by eight because there are eight carbons in phenoxyethanol. So 12.01 g per mole multiplied by eight, gives me 96.08 g per mole. And so for hydrogen, I'll take the molar mass of hydrogen and multiply this by 10. So 1.008 g per mole multiplied by 10, give me 10.08 g per month. And last but not least is the molar mass of oxygen multiplied by two. So that's 16.00 multiplied by two, gives me 32.00 g per mole. And so my final step is to go ahead and add all of my quantities together. So that's 96.08 added to 10.08 added to 32.00. And so this gives me a total molar mass of 138.16 g per mole and there you have it. So considering my answer choices, the correct answer is going to be oops option C in the multiple choice, the molecular formula of phenoxyethanol is C eight H 1002 and the molar mass is 138.16 g per mole. And so with that being said, thank you so very much for watching. And I hope you found this helpful.

Avobenzone is a common ingredient in sunscreen. Its structural formula is shown.
b. What is the molecular formula and molar mass of avobenzone?

Key Concepts

Molecular Formula

Molar Mass

Structural Formula

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