Question

How do you identify the number of ions a solute will have when dissolved in water

Answer 1

It depends on the compound you are dealing with. One of the easiest ways to go about this is to know (or memorize) a list of polyatomic ionic compounds - which is what you are likely studying. This list is more than you need to know but hey, doesn't hurt to know more than you need to http://www.fccj.us/PolyatomicIons/CompletePolyatomicIonList.htm
focus on these though http://www.chemistry.wustl.edu/~edudev/LabTutorials/PeriodicProperties/Ions/ions.html


For example, \(Ca_3(PO_4)_2\), this will "break apart" into 5 ions.

The key is in looking at the subscripts AND knowing that the phosphate ion \((PO_4^{-3})\) will stay together.

Answer 2

Well I already have the acetate,hydroxide,nitrite, nitrate, carbonate, sulfite, sulfate, phosphate, and ammonium polyatomic ions memorized i just don't understand how you break apart a compound.

Maybe I should just show you the problems im having trouble with.

1. Identify which solute will have the highest number of ions when dissolved in water.
A. nonelectrolyte ( i don't think its this one because strong electrolytes disolve completely into ions right?)
B. Al2 (CO3)3
C. CH3CH2OH
D. MgSO4

2. Which of the following is a strong electrolyte.
A. Ag2CO3
B. CH3CH2OH
C. C12H22O11
D. PbBr2
E. NH4Cl

I think if I know how to break up the compound into ions I can determine if it is a strong or weak electrolyte. Sorry if I dont know much on the subject my teacher only mentioned 2 things about electrolytes: if a solute is soluble it has strong electrolytes and if a solute is insouble it has weak electrolytes. Then she spent the rest of class teaching molarity. These questions are from the online homework that you get 2 attempts on and on the first attempt I got them wrong. I really want to figure them out cause I have a 89% and dont want to lose my 4.0 gpa. I am a freshman in college and I'm studying general chemistry 1. Thank you.

Answer 3

My advice to you is simple
1) Learn the names of the compounds
2) Learn to classify them based on their ionic/covalent properties in general.

Question 1
Now recall that for a compound to ionise in solution electrostatic bonds between ions must be broken and new bonds formed between the ions and water molecules. These are considerably weaker than any intramolecular (covalent, ionic) bonds but nevertheless must be stronger than inter-ionic bonds. Thus a so called non-electrolyte will not dissociate into ions and form strong bonds with water.

Let's look at the second compound. Al3(CO3)2 - what is its name?
You should be able to tell me Aluminium carbonate - an elementary question.
This tells you then the compound is comprised of two ions, aluminium ions and carbonate ions. Count how many of each are involved for a single ionic unit (or mole of aluminium carbonate). For Al, there's 3 Al3+ ions and for carbonate (CO3)2- there are 2 of those. That is inherent in the formula given.

So altogether you end up splitting the ionic compound into 3 cations (positively charged) and 2 anions (negatively charged) for a total of 5 ions. So every mole of aluminium carbonate generates 5 moles of ions!

Ok compound 3 - what is that? Notice its only got carbons, hydrogen and one oxygen there. The structure CH3CH2OH is an alcohol, specifically ethanol. The compound is polar but is purely a covalent compound because the weight of the C, H chain is not electronegative enough. Thus it does not have a 'natural' ionic form under normal conditions. This is another good hint for you. Is the compound ionic (generally involves metal-non metal interaction and is generally offered by the name of the compound with a salt suffix) or covalent overall? Organic compounds are generally always covalent in nature.

Compound 4 is straight forward - magnesium sulfate. Count how many lots of Mg and SO4 you have. You should see there are two moles of ions for every mole of MgSO4.

Question 2 follows by establishing a relationship between no. of ions generated and electrolyte strength.

Name the compounds one by one.

You should have silver carbonate, ethanol, sucrose (similar to glucose, a carbohydrate), lead bromide and ammonium chloride. Eliminate any covalent compounds there. Then count the ions of the remaining. You must know your polyatomic ions to do this well, but naming is already a very good start as it tells you what the compound will break apart into.

Answer 4

Thank you that really helped!!! @mww