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Problem 99 Hard Difficulty

Calculate the mass in grams of hydrogen present in 2.500 $\mathrm{g}$ of each of the following compounds.
a. benzene, $\mathrm{C}_{6} \mathrm{H}_{6}$
b. calcium hydride, CaH $_{2}$
c. ethyl alcohol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$
d. serine, $\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{O}_{3} \mathrm{N}$

Answer

A.0.1936 $\mathrm{gH}$
B.0.1197 $\mathrm{gH}$
C.0.3282 $\mathrm{gH}$
D.0.1678 $\mathrm{gH}$

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Top Chemistry 101 Educators
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Video Transcript

right. So here we have four compounds and we are finding the massive hydrogen. So let me write this down. We are finding something that we're finding. Just one thing is massive hydrogen mh So what we're gonna use And we've been told that the mess total of each compound is 2.5. So we put a question mark here. So we're looking for and we've been giving up the masterful 2.5 grams. And the formula that we're just gonna use is finding the mass percent of hydrogen because I once you find about percent hydrogen multiplied by the math total and then the massive engine No. Okay, so my percentages mass of hydrogen over mass of the compound, but not just one mass, one more of compound. So then that's one wall. Because we know that mass is moles multiplied by more maps, and we're always working in one more. So one more off compound multiplied by molar mass of the compound, and then one mall of, um, element, not one more. One more of a compound. And how many? How many ever hydrogen is that? Could be. So there is usually there is gonna be a factor that we're gonna multiply this by for to be one more compound. So it's gonna call it tax more so than a multiply fight. Yeah, still almost quiet it by a factor. So we're always dealing with a full more of compound that makes sense. So first off, we have benzene and we're finding the mass percent. So let's start for the bottom. The bottom is a bit. There's denominator fears a bit more straightforward. So one more multiply the molar mass of this cop. Moments of this compound is like 70. It's gonna move. Try to move fast so I can't really wait on these decimals, Gramps, she multiplied one more. But in moments not for hydrogen. There is a factor. Use my mistake in the previous video, but for it for a week. For us to have one more of the compound, we're going to have six as you. Many as more Sorry hydrogen atoms. So it's gonna be this X numbers on B six times molar mass of hydrogen, which is basically one. So when try and draw brackets 1.8 So OK, this right here will give us the proper mass percent. 7.7. Okay, Now we multiply this mass percent by the total mass, which is to survive for each element. Just 17% of 2.5. Oh, dear. 0.77 This is a gram. And then we go a massive engine, which is zero point 11 972 Right there we have it. Now it's the exact same thing at four. Calcium hydrate. So mass percent, starting with the denominator. It's one more multiplied by the molar mass of the compound. I have calculated as being 42 Gramps, with we've multiplied by a mole. Now the X for hydrogen, as you can see, is it to two multiplied by the molar mass of hydrogen. This, too, is what is making This one will crop up to make it the proper way. So this equals out to 4.7%. Let's just find 4.7% of our total mass, which will give us a very smart woman. Yeah, it will give us this number. Sorry. 0.11 972 Amiri's This This one here is 1.9 356 All right, and right here is was 0.0 0.11 17 and something to now we have ethanol or ethyl alcohol. Probably didn't do organic come yet, so I could make too much sense. But this a parent seems to be big, but it is a small molecule, so that's fine. Mass percent starting off the denominator, which is one more multiplied by the molar mass of the compound to find the mass of a Yeah, So if you add that up in equals 46 grams and now the X factor for indigent sewing to be three plus two this one, she's six. This likes Moeller Mm factor Don't apart by the molar mass to give us a mass. This percent then comes up to being 13 person. About 13% of our total mass of 2.5 gives us a mass of hydrogen men equals your plane. 32 your 0.3 to 81 eat Gramps. Last one, this Syrian, which is in amino acid. So our protein subgroup all right, monomer that the proper word for it also called the residue now one to find mass of compound who want to play one more by the molar Mass. It was compound which would give us 100 5 Mm. So now the ex forehead region seven. This smaller factor multiplied by mass. Give us mass. Excuse me, which is equivalent to 6.7% Now what's just multiply this percent by our total mass to finally get the mass of hydrogen being 0.167 You includes seven grams. It's trying to make that look nice. 167 grams. Wow. Once it seven Gramps appointment.

McMaster University
Top Chemistry 101 Educators
Stephanie C.

University of Central Florida

Lizabeth T.

Numerade Educator

Stephen P.

Drexel University

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