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Chemistry zarkam21:

How much does one sucrose molecule weigh in grams?

10 months ago zarkam21:

342.3

10 months ago Vocaloid:

hm, that would be an entire mole of sucrose, so to find 1 molecule you'd just divide that by avogadro's remember that a molecule is very very small

10 months ago zarkam21:

1.76 x 10^21

10 months ago Vocaloid:

342.3/(6.022*10^23) = ?

10 months ago zarkam21:

5.68 x 10^-22

10 months ago Vocaloid:

good

10 months ago zarkam21:

Find the number of ibuprofen molecules in a tablet containing 200.0 mg of ibuprofen (C13H18O2).

10 months ago zarkam21:

would I find the molar mass first of each element

10 months ago Vocaloid:

yeah, you'd add up 13(molar mass of carbon) + 18(molar mass of hydrogen) + 2(molar mass of oxygen) to find the molar mass of the whole compound then it's 200.0 mg/1000 to convert this to grams; then divide by the molar mass from the first step to get moles, then multiply by avogadro's to get molecules

10 months ago zarkam21:

7.834 x 10^26

10 months ago Vocaloid:

what did you get for the molar mass of ibuprofen

10 months ago zarkam21:

260.1898

10 months ago Vocaloid:

wait no

10 months ago Vocaloid:

the molar mass of ibuprofen should be closer to 206 not 260

10 months ago zarkam21:

yeah i rechecked my calculation I am getting 206.2852 now

10 months ago Vocaloid:

13(12.0107) + 18(1.00794) + 2(15.9994) = 206.28082g

10 months ago Vocaloid:

yeah that's fine, it's within rounding error

10 months ago Vocaloid:

after that it's just ( (200mg/1000) / 206.2852 ) * 6.022e23

10 months ago zarkam21:

5.839 x 10^20

10 months ago Vocaloid:

good that should be your solution

10 months ago zarkam21:

What is the mass of a sample of water containing 3.55×10^22 molecules of H2O?

10 months ago zarkam21:

this would be the opposite right take the molar mass of h20 and multiply by the given

10 months ago Vocaloid:

think about the units of molar mass g/mol; this doesn't have molecules in it since we have molecules we have to convert 3.55×10^22 molecules to moles first, then multiply by the molar mass of water

10 months ago zarkam21:

2.13781 x 10^46

10 months ago Vocaloid:

3.55×10^22 / (6.022e23) * 18.02 = ?

10 months ago Vocaloid:

remember, molecules to moles --> divide by molar mass

10 months ago Vocaloid:

|dw:1539661417976:dw|

10 months ago zarkam21:

1.06

10 months ago Vocaloid:

good that's what i got too

10 months ago zarkam21:

10 months ago Vocaloid:

yeah that's what i got too

10 months ago zarkam21:

What is the mass percentage of each element in the compound Al2O3?

10 months ago zarkam21:

Did you get 9% for Al if I did this right

10 months ago Vocaloid:

hm, I feel like it should be more than that molar mass of aluminum = 26.981538g molar mass of oxygen = 15.9994g total mass: 2(Al) + 3(O) = 2(26.981538g) + 3(15.9994g) just the aluminum: 2(26.981538g) so aluminium only/total mass * 100 should give the percentage

10 months ago zarkam21:

36

10 months ago zarkam21:

and then for O it would be

10 months ago zarkam21:

:

10 months ago Vocaloid:

hm, I got something a bit different

10 months ago zarkam21:

32 for oxygen

10 months ago Vocaloid:

2(26.981538) / [2(26.981538) + 3(15.9994)] = 52.9% composition of aluminum then for oxygen it's just 100% - 52.9% since we only have two components, aluminum and oxygen

10 months ago zarkam21:

Oh I see.

10 months ago zarkam21:

so it would be 52.9 , 47.1

10 months ago Vocaloid:

yes, 52.9 for Al and 47.1 for O

10 months ago zarkam21:

10 months ago zarkam21:

This is what I got. When going from grams to moles, it has nothing to do with avogadros # does it

10 months ago Vocaloid:

not quite have you tried calculating the molar mass of CaCO3?

10 months ago zarkam21:

Yes I got 100.091

10 months ago zarkam21:

and then divided the total by the number of grams given in the problem

10 months ago Vocaloid:

good, so you'd divide 25.45g/100.091g to get to moles, then you'd multiply by 3 since each molecule of CaCO3 has 3 mol oxygen

10 months ago zarkam21:

but I got 48 in the beginning for the molar mass. Would I still multiply by 3?

10 months ago Vocaloid:

48? no the molar mass is 100.091

10 months ago zarkam21:

no I mean when calculating the molar mass of the entire thing I already incorporated oxygen as being 3. In other words 16 * 3 . so why do I need to multiply by 3 again

10 months ago Vocaloid:

you have to incorporate oxygen into the molar mass to get 100.091 after you have moles, you have to multiply by 3 because it's asking for the number of moles of oxygen

10 months ago Vocaloid:

it's a completely separate calculation

10 months ago zarkam21:

oh okay I get it so I have to multiply by 3 in the beginning regardless because of the total molar mass but because its asking for oxygen I have to multiply by 3 again

10 months ago Vocaloid:

yes

10 months ago zarkam21:

.7628

10 months ago Vocaloid:

good that's it

10 months ago zarkam21:

10 months ago Vocaloid:

well you have 100g of the entire compound, and it says its composed of 40.0% carbon, 6.70% hydrogen, 53.5% oxygen, right? so how many grams of carbon hydrogen and oxygen do you have

10 months ago Vocaloid:

still there? since the percentages are out of 100 it's just 40.0g carbon, 6.7g hydrogen, 53.5g oxygen

10 months ago Vocaloid:

then you'd convert these masses to moles

10 months ago zarkam21:

40/100=.4 6.7/100=.067 53.5/100=.535

10 months ago Vocaloid:

hm, that's not how you convert grams to moles, remember g --> moles, divide by molar mass

10 months ago zarkam21:

but would I do 100 divded by molar mass or like the other number for the elements like for carbon 40/molar mass

10 months ago Vocaloid:

we started with 100g of a compound with composition 40.0% carbon, 6.70% hydrogen, 53.5% oxygen naturally, if we want to know the masses of carbons, hydrogens, and oxygen, we would do 100g * 40.0% = 40g of carbon; same reasoning gives us 6.7g hydrogen and 53.5g oxygen

10 months ago Vocaloid:

now, we want to convert 40g of carbon to moles by dividing by the molar mass of carbon, 6.7g hydrogen to moles by dividing by the molar mass of hydrogen and 53.5g oxygen to moles by dividing by the molar mass of oxygen

10 months ago zarkam21:

40/12.011=3.33 6.7/1.0079=6.65 53.5/16=3.34

10 months ago Vocaloid:

awesome, this gives us the molar ratio between the compounds, but since we want whole numbers, we divide all three quantities by the smallest quantity of the three so in simpler words, since the smallest number out of those three is 3.33, divide all three quantities by 3.33

10 months ago Vocaloid:

3.33/3.33 = 1 6.65/3.33 = about 2 3.34/3.33 = about 1 so the molar ratio is CH2O = your empirical formula = your sol'n

10 months ago Vocaloid:

anyway I haven't eaten all day so i'm gonna grab a quick bite, be back in an hour ish if you're still up for more hw

10 months ago
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