How do I determine how many anions or cations are in an equation??
Answer:
Anions are negative and cations are positive. They are usually right justified superscripts and this is where the consensus ends. Some authors prefer to write negative ions "--" and some use "-2". They will also do this with positive ions. The bad thing about plain computer text is that it has no superscripts. I have taken to using (+2) and (-2).
To find how many ions are in a chemical equation, just look for the "+" and "-" signs. Be aware that "+" is going to also be used to signify mixing reagents, such as "A + B = C". The term "A +" is not a positive "A" ion. The clue is that the "+" is not a superscript. One thing which never occurs is subtraction. There is no such reaction as "A - B = C".
One essential criteria for all ionic equations is they be balanced. To complicate matters, they have to be balanced both in charge and numbers of atoms. This branch of chemistry is known as "stoichiometry". Balancing consists of making sure there are equal numbers of atoms on either side of the "=" sign and that the sum of all the charges are zero. If one manages to balance the numbers of atoms, the charge usually balances as well.
Then, there are subscripts which indicate "phase". Are the atoms solids or gasses or dissolved in water? Working chemists (like me) hardly ever use subscripts, chiefly because we already know if something is solid or liquid or gas or dissolved in water. However, chemistry teachers tend to insist subscripts be used. Things then get really complicated in computer text because subscripts and superscripts just don't mix. For example:
Fe(s) + 2HCl(aq) = Fe(++)(aq) + 2Cl(-)(aq) + H2(g)
The above is what happens when solid ("s") iron ("Fe") is exposed to hydrochloric acid, ("HCl"). The acid is actually a 30% aqueous ("aq") solution of a very water soluable gas. It dissolves the solid ("s") iron ("Fe") into aqueous ("aq") ferrous cations ("Fe++") and negative chloride anions ("Cl-"). It also produces hydrogen ("H2") gas ("g"). In the equation above there is one cation and two anoins. The charge balances because 2 - 1 - 1 = 0. There is 1 iron atom, two chlorine atoms and two hydrogen atoms on either side of the "=" sign, so the equation is completely balanced.
A working chemist would simply write the reaction as "Fe + 2HCl = FeCl2 + H2" . We assume the iron is solid, the hydrogen is a gas and everything is taking place in water. looking at the iron product, we know the iron cation has a charge of +2, since we know the charge of the chlorine anion is always -1, and there are two of them. In short, the only critical things we need to know is what products will be produced from the reaction. The answer would be Ferrous chloride and Hydrogen. The most important thing to note is whether the iron cation is ferrous ("+2") or ferric ("+3"). If it were ferric, the equation would be:
2Fe + 6HCl = 2FeCl3 + 3H2
Most libraries are bound (sic) to have a few used intro college chemistry texts in the science and engineering section. This is the best reference to stoichiometry I can recommend, since there are also practice problems included as homework.
BTW: since the HCl is technically an aqueous solution, one can get really picky and write
Fe(s) + 2H(+)(aq) + 2Cl(-)(aq) = Fe(++)(aq) + 2Cl(-)(aq) + H2(g)
but this sort of thing is sure to annoy the supervisor. Real chemists also tend to use "<->" in place of "=" since many reactions are reversable.
You have to know, which part would be positive and which would take up a negative charge.
Like H2O.it is always H+ and -OH
Consider the equation to be electrically neutral.
That way you can calculate.
...sorry, even i took chemistry some years ago.
Cations are positively charged ions, for example Na+. Anions are negatively charged, example Cl-. Putting these together makes a neutral ionic bond NaCl.
The net ionic equation looks like this:
Na+ + Cl- = NaCl
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