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Chemistry 37 Online
OpenStudy (genny7):

Help please! Calculate each of the following quantities: A) mass in grams of 0.68 mol of KMnO4 B) moles of O atoms in 8.18 g of Ba(NO3)2 C) number of O atoms in 7.3x10^-3 g of CaSO4 x 2H2O

rishavraj (rishavraj):

mass = n*M n- no of moles M - Molar mass

OpenStudy (genny7):

Im still confused?

rishavraj (rishavraj):

A) mass = 0.68*158

OpenStudy (knowledge):

You have to find the molar mass of KMnO4. To find the molar mass, look at the atomic masses of each element in the compound and add them. You would 64 for oxygen instead of 16 because there are four oxygen atoms. The reason that you do this is because 1 mol of any substance has a mass in grams that is equal to the atomic mass of that compound or element. Thus, you add up all atomic masses for an element or compound to figure the mass in grams of 1 mol of that substance.

OpenStudy (ashley1nonly):

still need help

OpenStudy (genny7):

So basically i find the molar mass?

OpenStudy (ashley1nonly):

yes thats a start

OpenStudy (ashley1nonly):

(0.68 mol KMnO4) (molar mass)KMnO4 ---------------- ----------------- 1 1 mol KMnO4 the moles cancel leaving you with mass in grams

OpenStudy (ashley1nonly):

molar mass is when you add all of the weights up

OpenStudy (knowledge):

you find the molar mass, yes, I will do a for you \[.68 mol KMnO_{4} (\frac{ 158 g }{ 1 mol })\]

OpenStudy (knowledge):

1 mol of KMnO4 has 158 grams in it

OpenStudy (ashley1nonly):

for every one mole it equals the molar mass of whatever compound or KMnO4 for this case

OpenStudy (ashley1nonly):

yep

OpenStudy (knowledge):

@genny7 do b here

OpenStudy (genny7):

Okay

OpenStudy (genny7):

8.18 mol Ba(NO3)2 (261/1 mol)

OpenStudy (ashley1nonly):

8.18g of Ba(NO3)2

OpenStudy (ashley1nonly):

you started with g so how did you just switch to moles

OpenStudy (ashley1nonly):

your units must cancel out

OpenStudy (genny7):

Oops i put moles instead of g

OpenStudy (ashley1nonly):

8.18g of Ba(NO3)2 1 mol Ba)NO3)2 ----------------- -------------- 1 (molar mass Ba(NO3)2

OpenStudy (ashley1nonly):

then you use the mole to mole ratio continuing the equation, you can do math at end

OpenStudy (ashley1nonly):

8.18g of Ba(NO3)2 1 mol Ba)NO3)2 (# mole of O in Ba(NO3)2 ----------------- -------------- ---------- 1 (molar mass Ba(NO3)2 1mole Ba(NO3)2

OpenStudy (ashley1nonly):

it leaves you with mole O

OpenStudy (genny7):

Where the molar mass is at would that be 1?

OpenStudy (ashley1nonly):

then to get to av's 3 continue by adding 6.022*10^23 ---------- mole 0

OpenStudy (ashley1nonly):

3=#

OpenStudy (ashley1nonly):

you add all the masses of Ba(NO3)2= BaN2O6

OpenStudy (ashley1nonly):

do you understand

OpenStudy (genny7):

Ehhhh kind of?

OpenStudy (ashley1nonly):

the molar mass is the mass of whatever compound you use so since we have Ba(NO3)2 ***we have to take note that for (nO3)2 there's a 2 on the outside so we will multiply that in which will give us BaN2O6 now we calculate the molar mass by adding all the weights which is located on the periodic table Ba=137.3 N=14.01 multiply b 2 O=15.99 multiply b 6

OpenStudy (genny7):

Okay i know how to find the molar mass...the thing is that i dont understand why you have to cancel out the mol?

OpenStudy (ashley1nonly):

if you keep moles you can go to grams its like saying you want to change a 100 pennies into 1 dollar. in order to get to the dollar you have to drop the cents sign correct.

OpenStudy (ashley1nonly):

cant

OpenStudy (genny7):

Oh oka, does grams ever change?

OpenStudy (ashley1nonly):

when you go to avogrados # it cancels out

OpenStudy (genny7):

And how does avogrados work?

OpenStudy (ashley1nonly):

i have the final equation above, but you have to have moles in order to go to avogrados # heres what we are doing grams---moles---avogrados#

OpenStudy (genny7):

Ahhhh okay im starting to get the hang of it :)

OpenStudy (ashley1nonly):

yep takes practice to get it down.... always make sure your unit cancel out... if they dont cancel then youve messed up or could place the numbers in the wrong place

OpenStudy (ashley1nonly):

you have everything you need to solve just how many moles of O are there

OpenStudy (ashley1nonly):

do you know how many

OpenStudy (genny7):

Is it 4.92436x10^24?

OpenStudy (ashley1nonly):

noooo and just re-reading the comment when you said when does grams cancel out. it cancels when you go to moles...sorry Ba(N03)2 you are looking for mole of O you multiply the 2 in BaN2O6 now you have a total of 6 moles. or are you asking for the final answer

OpenStudy (genny7):

Oh okay, nah i want to see if i can find the answer by myself

OpenStudy (ashley1nonly):

ok, you officially have all of the answer to solve you math just has to be correct, you also have the equations good luck

rishavraj (rishavraj):

@genny7 good girl gonna find answer urself........

OpenStudy (genny7):

Thanks soooo much @Ashley1nOnly & thanks soooo much for your time :) i have learned quite alot today thanks to you :)

OpenStudy (genny7):

Lol thanks @rishavraj

OpenStudy (ashley1nonly):

you're welcome

OpenStudy (genny7):

:)

rishavraj (rishavraj):

u r welcome....lol

OpenStudy (genny7):

Lol :)

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