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Problem 119 Hard Difficulty

Calculate the percent by mass of the element mentioned first in the formulas for each of the following compounds.
a. sodium azide, NaN $_{3}$
b. copper (II) sulfate, CuSO $_{4}$
c. gold(ili) chloride, AuCl$_{3}$
d. silver nitrate, $\mathrm{AgNO}_{3}$
e. rubidium sulfate, $\mathrm{Rb}_{2} \mathrm{SO}_{4}$
f. sodium chlorate, $\mathrm{NaClO}_{3}$
g. nitrogen triiodide, $\mathrm{NI}_{3}$
h. cesium bromide, CsBr

Answer

A.35.36$\%$
B. 39.81$\%$
C.64.94$\%$
D.63.50$\%$
E.64.02$\%$
F.21.59$\%$
G.3.549$\%$
H.62.45$\%$

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Video Transcript

All right. So here we have eight on chemical compounds, and we're going to find the mass percent off the first element present. Let's recall the mass percent formula. The way we calculated it is we take the mass of the element, whatever element in question, massive the element and divided by the total mass but the total mass of one mole of substance, like one wall of the chemical. All right, so first, we have, um, sodium a site, and we're gonna start off by listing each moment in this chemical compound. Now we're going toe. Calculate the mass of each compound. So let's remember little formula for mass. We can go to it mass, both heating malls, multiplying it. But Moeller muss. All right, so we know we have one mole of substance, one mole of sodium a side. So if you have one more sodium a site, that means we also have one more off sodium. And that means we then have three moles of nitrogen, right? And then we'll multiply by the molar mats of each substance. Sodium small amounts is all right. 22.98 months of in Seoul, right, 23 actions. More mass is 14 dams Permal. And once we told this up, we get 65 which is now our mass total. So no, the mouse percent sodium. The first element somebody gonna be this 23. That's the mass of sodium. Over the mass. Total 65. Well, these were both Ingram's. You take your jocular and polling food more off the pigeons, we get a mass percent off 35 point 36 All right. Okay, let's move on. Next. We have copper soffits. We're gonna do the exact same, um, methods list up the elements, and now calculate the mass of each element so you can find a whole mouse. All right, so remember, always one more of the chemical. More copper to selfie. So one more of copper. Two sulphate is one off copper. One more sulfur and formals of oxygen. And we'll multiply these moles by the more mouse of the substance of the element. I'm here. We've now committed mass. Okay? No, on three. Some. All of these masses up, we get 159 0.6, just the total mass. Then we'll take the massive copper drawing looking for the mass percent off the first element. Math percent of copper is the mass of Klepper over the tomas 0.6. Okay, Not equals 39.81 remind 0.81 person's. Okay, well, that's really but faster. Here we have gold. Three chlorate. So yep. Gonna list out each compound. Men calculate their mass. One more off gold and one more awful to chloride. Courtnall. Masts 1 96.9 And your three moles off court. Can we find the total mass, which is 300 country in the months percent of gold is just this mouth over the Thomas. It gives us a mass percent 64 0.9 four. You hit next. We have silver nitrate do the exact same thing. One more silver nitrate. It's Gwen Moore Silver. So there's more mass. It's 107 0.8. You have one more off nitrogen Khiry of three moles of oxygen. Okay. And that summed up is one 70 around him. Kate. Then the mass percent for silver shut mass of the element over mass total. Here's a 63.5%. Next, we have obedient, so feet. Heavens, he bidding before it's an alkali metal group one. Okay, so it's first list out each element. Okay, so here we have two moles of rubidium, not the usual one. And it's more masks, 85.5 grams from oops, 85.5 grams. Next we have one will. So, feet. So if you're wondering us, I am looking at the sub scripts here that tell us the number off each Adam to find moms. True. And the oxygen formals. More massive. Look, 15.9994 grams per mole. And the total sum is to 67. All right, so most percent of rubidium is two multiplied by 85 to take the Thomas, then divided by to 67 to give us 64 point Oh, 2% Next up, sodium. Correct. So yet again, it will was talked each element. Then find number of moles of the element multiplied by the molar Mass of the element Do the same thing for each. Adam. Also, this is also how we would calculate, um, moment mass you. But you know, Yeah, we were actually moments in the exact same way, but we wouldn't be using Matt moles multiplied by more mouth. That formula, Thank you. Ate it. Is that more mass is the molar mass of each element and the some of that. So it isn't a mold. Multiple of another mass calculation, but a number at us. So then math present. The podium is trying to put nine over the total mass. It gives us 21.6%. Hey, next up, we have certain are right. Next region Try died. Well, we just list out the mess. Every element you forget I died is a college in So group 17 True. This then sums up 23 94 grams Okay, mass percent of nitrogen then would be 3.55%. So quite small. Just this very large item I died is taking up all of that wheat. Oops. Look. Must want this caesium bromide Caesium. It's right under rubidium. See your winery? Que so we have one mole of each to these elements. 1 32.9 grams promote for caesium and Romy. 79 0.9 grapes for more. Here the total mass 2 12 mass percent proceed iam its massive element over mass total because a 62.45%

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