[labec]

The question says:

From the information below, determine the mass of substance C that will be formed if 45.0 grams of substance A reacts with 23.0 grams of substance B. (Assume that the reaction between A and B goes to completion.)

a.) Substance A is a gray solid that consists of an alkaline earth metal and carbon (37.5% by mass).  It reacts with substance B to produce substances C and D.  Forty million trillion formula units of A have a mass of 4.26 milligrams.
b.) 47.9 grams of substance B contains 5.36 grams of hydrogen and 42.5 grams of oxygen.
c.) When 10.0 grams of C is burned in excess oxygen, 33.8 grams of carbon dioxide and 6.92 grams of water aree produced.  A mass spectrum of subbstance C shows a parent molecular ion with a mass-to-charge ratio of 26.
d.)Substance D is a hydroxide of the metal in substance A.

I seriously need help.  I can't even begin the problem:/ If you know how to do this and feel like trying please list your steps accordingly.  Thanks!

[Arkcon]

Well, lets try and see what you do know.  Can you break this question apart, into balanced chemical reactions, using a placeholder, like X, for the unknown element?

Also, can you express this part --

The question says:
*SNIP*Forty million trillion formula units of A *SNIP*

in exponential numbers?

[labec]

Sadly, I haven't learned how to do that yet.. so as for the exponential function 4.0 x 10?

[sjb]

I would assume, given the use of both million and trillion in the same sentence that this means 10²⁴, and that trillion is being used in the long scale sense of 10¹⁸, but this seems to make a very small relative molecular weight....?

BTW Arkcon, good to see you back, how's things?

S

[DrCMS]

No in this question a trillion is 10¹² so 40 million trillion is 4x10¹⁹ molecules.

Overall it looks complicated but it is actual quite a simple question.

[sjb]

Well, yes, if it is short scale trillion things are a lot easier, but why use million and trillion in the same sentence, why not just say quintillion?

Anyway 4x10¹⁹ formula units have mass 4.26mg, what does this tell you about the solid...

[labec]

Ok from the formula I found I got the answer to be 16.64 grams?  Is this right?

[DrCMS]

Yes 16.6g acteylene. Note the number of signifcant figures in the question and my answer.

[labec]

OK thank you!:)

[sapphiregirl]

From the information below, determine the mass of substance C that will be formed if 45.0 grams of substance A reacts with 23.0 grams of substance B. (Assume that the reaction between A and B goes to completion.)
 
a.) Substance A is a gray solid that consists of an alkaline earth metal and carbon (37.5% by mass). It reacts with substance B to produce substances C and D. Forty million trillion formula units of A have a mass of 4.26 milligrams.
b.) 47.9 grams of substance B contains 5.36 grams of hydrogen and 42.5 grams of oxygen.
c.) When 10.0 grams of C is burned in excess oxygen, 33.8 grams of carbon dioxide and 6.92 grams of water aree produced. A mass spectrum of subbstance C shows a parent molecular ion with a mass-to-charge ratio of 26.
d.)Substance D is a hydroxide of the metal in substance A.
 
so for step A i assumed that that Carbon had a mass of 3/8 of the total meaning the total amu is 32, which leaves 20 amu for the metal. the only metal that fits this is Be.
 
then for step B H20 was really the only substance hydrogen and oxygen that fit these ratios:
 
2/18 = .1 and 5.36/47.9 = 1
likewise, 16/18 = .89 and 42.5/47.9 = .89
 
so now i have Be2C + H20 -> C + D
 
for step C i wrote out a whole stoich chart and when i solved it i got C2H2 or HC2H for substance C
here's my stoich chart:
 
Balanced Equation 2C2H2 + 502 -> 4CO2 + 2H20
Molar Ratio 2 5 4 2
Molar Mass 26 32 44 18
Grams 10.0 30.72 23.8 6.92
Moles .38 .96 .77 .38
 
also (2/18) = (x/6.92) yields .8 grams of Hydrogen meaning out of the water 6.12 grams are oxygen
and (16/18) = (x/33. yields 9.2 grams of Carbon meaning out of the carbon dioxide 24.6 grams are oxygen
6.12 plus 24.6 gives you 30.72 hence the 30.72 grams of oxygen in the chart
everything else was either given or solved from there
 
then for step d it says that substance d is the hydroxide of the metal in substance A so Be(OH)2
 
putting that all together gives you the equation
 
Be2C + H2O -> C2H2 + Be(OH)2
 
but i can't balance that equation

I know Be2C doesn't have the exact percentage of carbon that I need but I don't know what substance A could possibly be.

[DrCMS]

so for step A i assumed that that Carbon had a mass of 3/8 of the total meaning the total amu is 32, which leaves 20 amu for the metal. the only metal that fits this is Be.

Think again, nowhere does it say there can only be one carbon substance A.

then for step B H20 was really the only substance hydrogen and oxygen that fit these ratios:

Yes you got that bit right, B is water.

so now i have Be2C + H20 -> C + D
 
for step C i wrote out a whole stoich chart and when i solved it i got C2H2 or HC2H for substance C
here's my stoich chart:
 
Balanced Equation 2C2H2 + 502 -> 4CO2 + 2H20
Molar Ratio 2 5 4 2
Molar Mass 26 32 44 18
Grams 10.0 30.72 23.8 6.92
Moles .38 .96 .77 .38
 
also (2/18) = (x/6.92) yields .8 grams of Hydrogen meaning out of the water 6.12 grams are oxygen
and (16/18) = (x/33. yields 9.2 grams of Carbon meaning out of the carbon dioxide 24.6 grams are oxygen
6.12 plus 24.6 gives you 30.72 hence the 30.72 grams of oxygen in the chart
everything else was either given or solved from there
 
then for step d it says that substance d is the hydroxide of the metal in substance A so Be(OH)2
 
putting that all together gives you the equation
 
Be2C + H2O -> C2H2 + Be(OH)2
 
but i can't balance that equation

You've got C correct but because you've got A wrong then so is D, that means you can't balance the equation.

I know Be2C doesn't have the exact percentage of carbon that I need but I don't know what substance A could possibly be.

Look at the other alkaline earths one of them forms a compound that is 37.3% carbon and reacts with water to give C₂H₂ plus the corresponding hydroxide.

[sapphiregirl]

i really have no idea what it could be. is the formula that i'm looking for M2C (where M is the metal) because if that's the formula then none of the metals fit. If you could please point me in the right direction, i'd greatly appreciate it. Thanks for all the help.

[Arctic-Nation]

You need to look for MC₂.

(Edited twice because of extremely terminal stupidity. It's a miracle I remember how to breathe.)

[sapphiregirl]

that doesn't exist. Carbon has a charge of 4- and alkaline earth metals have a 2- charge, right? or can carbon sometimes have a 1- charge because i know that alkaline earth metals always have a 2- charge.

[Arctic-Nation]

Edit: looks like I shouldn't be posting at this moment of the night, but you're looking for MC₂. The carbons are covalently linked, which explains the apparent charge difference.