Terminology Clarfication [ENDORSED]

[Sonam Sidhu 2J]

"Calculate the molar mass of copper(II) sulfate pentahydrate."

What does the (II) attached to the copper element mean? And how does it affect the molar mass or any part of the compound?

Also, are we expected to instinctively know the elements that make up a compound when it is written out this way?

[Kathleen Nguyen 3G]

After what I've read, the roman numerals are based on the "stock system" in order to help name compounds with multivalent metals. They supposedly tell the charge of that certain metal- copper (II) has a charge of 2+ (I believe).

In relation to that, bother copper and copper (II) have a 2+ charge.

I assume that we will be given some sort of periodic table so we will know the elements and their charges, but we probably will need to know the other details.

[Sonam Sidhu 2J]

Thank you very much for the clarification.

[awidodo]

The numbers in the brackets actually indicate the amount of positive charge the copper ion has. Copper I is Cu+, and has a single positive charge and Copper II is Cu2+, with two positive charges.

[Sheel Shah 1H]

Cu (I) has one positive charge, whereas Cu (II) has two positive charges. This is very important to know, especially when you are trying to find the formula for a specific compound (since the overall charge must always balance out).

These types of metals are called "multivalent metals" because of the multiple charges associated with them.

Another example is iron.

Best of luck!!

-Sheel Shah

[Varsha Sivaganesh 1A]

I think once we begin learning to name compounds this will make more sense. Typically, when you name compounds that contain a transition metal + a nonmetal, you must indicate the charge of the transition metal, since some have multiple charges. For example, Fe2O3 would be written as iron (III) oxide, because the charge of Fe is 3+ in this case.

[Jessica Schirmer 1J]

On this topic, I'm curious about their original question of if it affects the mass of the transition. I would assume not, or at least not significantly since electrons have a very small mass, but I was wondering if anyone else had input on that!

[Chem_Mod]

Sheel is entirely correct, the number in brackets indicate the positive charge associated with the metal in question. And in response to Jessica's question, the charge on the metal ion will not affect the mass of the element in question. That is to say, the mass of Fe(III) is equal to the mass of Fe(IV) is equal to the mass listed in the periodic table for Fe. Good luck!