According to the rules of nomenclature, calcium carbide must have the formula Ca2C, but the actual formula is CaC2, why?

Can someone please explain very briefly? (briefly because I am just doing a stoichiometry problem that says "calcium carbide reacts with water to form calcium hydroxide and acetylene (HCCH)...etc", but the formula for calcium carbide is NOT given (that's silly and crazy). But clearly anyone who is attempting this problem must know what calcium carbide is...and there's no way to figure out what it actually is...

I never had a good grip on the rules of chemical nomenclature, but here's a link for you:

http://en.wikipedia.org/wiki/Calcium_carbide


Or. From the page on carbides (http://en.wikipedia.org/wiki/Carbide):

"In chemistry, Carbide may refer to three different things:

1. The polyatomic ion C₂²⁻, or any salt of such. There is a triple bond between the two carbon atoms.

2. The monatomic ion C⁴⁻, or any salt of such. This ion is a very strong base, and will combine with four protons to form methane: C⁴⁻ + 4H+ → CH₄.

3. A carbon-containing alloy or doping of a metal or semiconductor, for example, steel."

IUPAC is the body that standardizes chemical numenclatures. Some of the formulars are questionable but many chemistry teachers have told me to just "DO AS THEY SAY". Chemical formulars are not naturally standard, compounds can have any structure in any part of the earth given the right condition, which is why we just take whatever IUPAC gives us. Believe me, I will be a chemistry major in a few months. I know what you are thinking; that 2 atoms of Ca joins 1 atom of C to attain octet structure. Technically you are right but IUPAC does what they do for a reason only the CIA and FBI knows. Just take the formulas for what they are sometimes and you will be fine, trust me.

here is more info if you want it:
http://www.matweb.com/search/SpecificMaterial.asp?bassnum=EINOR0106

Isn't that the stuff used in miner's lamps?

Then how can I do a stoichiometry problem given the reactant "calcium carbide"?

CaC2 + 2H20 = Ca(OH)2 + C2H2

Then how can I do a stoichiometry problem given the reactant "calcium carbide"?

Just do as Valich has done, balance the equation first, then take it from there, but remember to use IUPAC's given formulars and you will be fine. Trust me. Always look up the given formulars before starting to balance the equation, don't make up yours first. My best advice is to ask your teacher what he thinks, 9 times out of ten he or she will say "use IUPAC", some less conservative teachers will ask you to use your own formular. Just ask, I have had the same problems before.

But how do you know that calcium carbide has the formula CaC2?

C = carbon, C2 = carbide. By definition, carbide is a "binary" compound of carbon. "Binary" means two. You will find exceptions in the chemical formulas of certain carbides when you deal with ions and isotopes, but I'm not sure you can understand this without taking a course in chemistry.

"bi" also always means "two" and the suffix "ide" is added to many chemicals, such as chloride, cyanide, monosaccharide. This either means that it is a binary compound, or is added to the contracted name of the element to indicate its electronegativity. For example, when the element chlorine (Cl) is found in pairs it is called chloride: Cl2, but a cyanide ion CN- is still called cyanide indicating its electronegativity. therefore, in this sense, with the addition of "ide," there is some inconsistency, but this should have nothing to do with your applications of the term carbide.

How do you know that calcium carbide has the formula CaC2?

Because this is it's basic molecular formula! If you were dealing with an ionic structure of it, then other ionic chemicals would be present to come into play to change its ionic arrangement. But your stoichiometry problem is not dealing with this and has not presented any parameters of extraneous ionic elements that would change this basic molecular formula of calcium carbide. So just use the basic formula.