How many total atoms are there in 0.550 mol of potassium bromite (KBrO2)?

Question

I REALLY NEED HELP WITH THIS 

Answer 1

Dear MCKENZEE,

No problem here. Think of this salt (KBrO2) as a molecular entity, that is, one molecule of it has the atoms: 1 potassium, 1 bromine, and 2 oxygens. It doesn't really have that form -- it's a salt with alternating K+ and (BrO2)- ions -- but for this problem think of it as a single molecule. Then that one molecule has 1+1+2 = 4 atoms, right? 

Now, that 4-atom cluster is the unit measure that feeds into your next stage, namely, taking 0.550 moles. How many units is an Avogadro's number of units? 6.023*10^23 units, right? So you have:

4 atoms/unit  * 6.023*10^23 units/mol * 0.550 mol = you do the math.

Let's review. When you have a chemistry (or any other type of!) problem involving converting from one type of units (here, the salt formula, and the #mol) to another type of unit (#atoms), you must work systematically to proceed from one end to the other. In this case, working conceptually from a small unit to a larger one was easy to visualize; in many other cases, you can write an expression for the solution by starting with the given value (0.550mol KBrO2) and multiplying by successive identities (which here could be x (6.023*10^23 KBrO2/mol KBrO2) * (4 atoms / KBrO2) which convert from your starting unit of measure (mol KBrO2) to your desired ending unit of measure (atoms). The trick here is to keep a strict scrutiny on exactly what your units are at each identity -- when your units come out right, then your calculations come out right, too.

-- Stanton de Riel