How many moles of ions are in the following?

Question

(b) 0.182 mol K₂CrO₄ 

 

(c) 0.630 g Ba(OH)₂ 

(d) 1.48  10^-9 mol Na₂CO₃ 

I have no idea how to do this.

Answer 1

Hi Eli O.,

So if you can't do any of these, the problem is that you can't convert from a molecular (or salt) formula to ions, as a number thing.

So what is a salt?

It has one or more cations, and one or more anions, with various (+) and (-) charge(s) respectively.

Let's look at your items.

K2CrO4 : potassium chromate. the K's are each K(+1) ions, but the CrO4 is an oxyanion (means it has oxygens plastered onto something else, in this case Cr) . the CrO4 is a (-2) ion.

So overall, you have 3 ions for each formula unit of the salt, and you multiply the given #moles of the salt by 3 to get the #ions.

Ba(OH)2 : I assume you can add up the atomic masses, to convert to #moles. Then:

Ba is always (+2) in salts; (OH) is always (-1), so you have the charges balanced to neutral as you must. That's 3 ions per mole of Ba(OH)2.

Na2(CO3) : solves just like the K2CrO4 above. (CO3) is always a (-2) ion. You could either just know this already, or figure it must be in order to balance 2 Na's, or calculate it de novo from CO2 (neutral) + O (always calculated as (-2) since it adds 2 e- to get to that "full shell" condition) = 0-2 = -2.

Eli O.: if you are indeed clueless about how to manoever around a chemical formula and get basic information about it, I recommend you get a few minutes help from a savvy peer or your instructor. That's far more time-effective than asking on Wyzant.

-- Cheers, --Mr. d.

Answer 2

Hi Eli O.,

So if you can't do any of these, the problem is that you can't convert from a molecular (or salt) formula to ions, as a number thing.

So what is a salt?

It has one or more cations, and one or more anions, with various (+) and (-) charge(s) respectively.

Let's look at your items.

K2CrO4 : potassium chromate. the K's are each K(+1) ions, but the CrO4 is an oxyanion (means it has oxygens plastered onto something else, in this case Cr) . the CrO4 is a (-2) ion.

So overall, you have 3 ions for each formula unit of the salt, and you multiply the given #moles of the salt by 3 to get the #ions.

Ba(OH)2 : I assume you can add up the atomic masses, to convert to #moles. Then:

Ba is always (+2) in salts; (OH) is always (-1), so you have the charges balanced to neutral as you must. That's 3 ions per mole of Ba(OH)2.

Na2(CO3) : solves just like the K2CrO4 above. (CO3) is always a (-2) ion. You could either just know this already, or figure it must be in order to balance 2 Na's, or calculate it de novo from CO2 (neutral) + O (always calculated as (-2) since it adds 2 e- to get to that "full shell" condition) = 0-2 = -2.

Eli O.: if you are indeed clueless about how to manoever around a chemical formula and get basic information about it, I recommend you get a few minutes help from a savvy peer or your instructor. That's far more time-effective than asking on Wyzant.

-- Cheers, --Mr. d.