help with chemistry!!

[lpfan07]

Does anyone know how to figure out this problem? What is the mass of oxygen contained in 125 grams of CaCO3

A compound has a molar mass of 92.0g/mol and its percent composition is 69.6% oxygen and 30.4% nitrogen. What is its molecular formula?

Determine the molecular formula of a compound with molar mass between 105 and 115 g/mol with contains 88.8% Carbon and 11.2% Hydrogen.

In 2.50 mol of Ba(ClO3)2, a) how many moles of barium ions are present? B) How many moles of chlorate ions are present? C) How many moles of oxygen atoms are present?


I need to see all the work and the correct answers. Any help will be greatly appreciated. Act quickly because I need the answers because this is due tomorrow!

Thanks,

Lindsey

[The Girl From Ipanema]

I'm probably late on this and you're probably done doing your assignment but here's what I've layed out for you in case you still need help....

Originally Posted by lpfan07

What is the mass of oxygen contained in 125 grams of CaCO

For this problem you convert the grams of CaCO given to you in the problem to moles of CaCO3 by multiplying by the conversion factor of mol/g

Ie. 125 g CaCO3 x 1 mol CaCo3/100.088g CaCO3 x 16g O/1 mol O = 19.982g O

I got the 100.088 g from adding the atomic mass units of each of the elements in the compound aka molecular weight

I got 16 g O because we know that one mole of O is equal to the atomic weight of the element.

A compound has a molar mass of 92.0g/mol and its percent composition is 69.6% oxygen and 30.4% nitrogen. What is its molecular formula?

For this problem assume 69.6% to be 69.6 grams ....so we would have 100 g of the entire substance....69.6 of it is Oxygen....you have to convert it from percent to grams....

69.6 g O x 1 mol O/16 g O = 4.35 mol O

30.4 g N x 1 mol N/14 g N = 2.17

to get an even ratio you divide all of the above answers by the smallest number

so we divide by 2.17:

4.35/2.17 = 2
2.17/2.17= 1

so molecular formula = NO2

Determine the molecular formula of a compound with molar mass between 105 and 115 g/mol with contains 88.8% Carbon and 11.2% Hydrogen.

I'm really not sure why they give you 105 and 115 because this question can be done without those numbers....which leads me to believe that I might be missing something in the question....because teachers don't give you extra numbers for no reason....(at least most of the time they don't)

this question is just like the last one:

assume 88.8 g CARBON and 11.2 g HYDROGEN

88.8 g C x 1 mol C/12 g C = 7.4 mol C

11.2 g H x 1 mol H/1 g H = 11.2 mol C

divide by smallest number....which is 7.4 so:

11.2/7.4 = 1.5
7.4/7.4 = 1

you will notice that we don't have a clean number (1.5) so you need to multiply BOTH numbers by a common factor to make it a whole number

1.5 x 2 = 3
1 x 2 = 2

so formula is: C2H3

In 2.50 mol of Ba(ClO3)2, a) how many moles of barium ions are present? B) How many moles of chlorate ions are present? C) How many moles of oxygen atoms are present?

Start with what you are given which is 2.50 mol Ba(ClO3)2

and convert from moles of this substance to the moles of each individual element

I'm gonna substitute # = the barium compound so that I don't have to write that formula out everytime
2.50 mol # x 1 mol Ba/1 mol # = 2.50 mol Ba (because there is no coefficient or subscript indicating more than one Ba in the formula)

now for the next elements you have to check the subscripts and coefficients (there aren't any coefficients in this one though)

2.50 mol # x 2 mol ClO3/1 mol # = 5 mol ClO3 (this is because if you look outside the brackets it has a subscript of 2....this 2 indicates the quantity of ClO3 in your formula)

2.50 mol # x 6 mol O/1 mol # = 15 mol O (subscript of 2 outside the bracket multiplied by subscript 3 inside the bracket = 6 moles of oxygen)

I THINK this is right but I haven't done this in since first year university LOL so I may be a bit iffy on it....

Hope that helps

[Fearless™]

Nice one Jubolly! ~reps for being so clever~

[sharlene]

i did chemistry :S i hated every minute of it, and surprisingly i got one of the best grades for it in my exams. sorry this is of no relevance to your problem xD

[Fearless™]

Originally Posted by sharlene

i did chemistry :S i hated every minute of it, and surprisingly i got one of the best grades for it in my exams. sorry this is of no relevance to your problem xD

O_O well, maybe the rest of the ppl in your class all failed? lol. I hate chemistry >.<

[The Girl From Ipanema]

I hated chemistry in HS, but really liked it in university....

overall physics was my favorite science in HS.....i hated biology in HS and still hate it now

[That Kid with the Hair]

Chem is amazing....but hard.

[tutmos]

dude i love chemestry i had a 100% in that class as a final grade

[That Kid with the Hair]

wow...wrong place.

[Western_Samurai]

Here's how i feel about the sciences:
computer science>physics>chemistry>all of the other sciences besides biology>some more stuff>biology