Chemistry - Net ionic equations, ionic solids

In summary: Aluminum sulfate is comprised of 2 aluminion ions each with a +3 charge and 3 sulfate ions each with a -2 charge. This, as you can see, gives a neutral ionic compound with no charge.
  • #1
kaitamasaki
20
0
I am having a review test soon and I was not taught anything about ionic stuff last year, I have no idea what it is at all.

Sample questions look like:

"which of the following compounds are considered to be ionic solids? If it is an ioni solid, write an equation showing the dissociation of the compound as it dissolves in water"

eg. NiCl2, ClF5, NaOH

First I have no idea what an ionic solid is. why is it even dissociating when it dissolves in water. How would I know if its ionic solid or not?

I have to write an equation. Is it like decomposition, single replacement, synthesis that kind of equation? what becomes reactant or the product? I have no idea what is happening! Is part of this requiring memory work, or is it all mathematical, or do i have to refer to the periodic table, or is it logic, or do I have to think about it? I am totally lost:rofl:

Also I have a question like this:

Ca(OH)2 has low solubility. write the net ionic equation for the reaction that occurs when NaOH(aq) is mixed with Ca I2 (aq) Identify the spectator ions.

I have the answer but I totally don't know how it came up. How do i know if something is positive or negative charge? What becomes solid or liquid?

If someone could clarify this all up for me, that would be really appreciated
 
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  • #2
kaitamasaki said:
I have to write an equation. Is it like decomposition, single replacement, synthesis that kind of equation? what becomes reactant or the product? I have no idea what is happening! Is part of this requiring memory work, or is it all mathematical, or do i have to refer to the periodic table, or is it logic, or do I have to think about it? I am totally lost

There are some exceptions to the statements I am going to make, but for basic chemistry you should not need to worry about them.

Ionic compounds are those compounds that have a metal and a nonmetal. You can use the periodic table to determine what is a metal/nonmetal/metalloid. An example is NaCl. Na (sodium) is a metal and Cl (chlorine) is a non-metal. Hence NaCl, sodium chloride, is an ionic compound.

Ionic compounds break up into their respective ions when they dissolve in water. Sodium chloride breaks up into sodium ions and chloride ions. The +1 charge on the sodium ion and -1 charge on the chlorine ion cancel each other giving a neutral ionic solid of NaCl. So your equation showing its dissociation in water would look like this:

NaCl(s) --> Na+(aq) + Cl-(aq)

(s) means solid (aq) means aqueous (in water)

Another example is aluminum sulfate, Al2(SO4)3. Now in this case you have more than 2 atoms in your ionic solid. SO4-2 is what is called a polyatomic ion. The naming of these compounds is something that you pretty much have to memorize. There are some patterns for naming them, however. Aluminum sulfate's dissociation in water would look like this:

Al2(SO4)3(s) --> 2Al+3(aq) + 3SO4-2(aq)

Aluminum sulfate is comprised of 2 aluminion ions each with a +3 charge and 3 sulfate ions each with a -2 charge. This, as you can see, gives a neutral ionic compound with no charge.

The second question you ask has to do with a class of reactions called double displacement reactions. Double displacement reactions can occur if a) one of the potentially formed products is not very soluble (ie a precipitate is formed), b) if a gas is formed, or c) if it is a acid-base neutralization reaction. If the mixture of reactants does not belong to one of these three categories, then the reaction will not occur and all you will have is a bunch of ions in solution.

kaitamasaki said:
Ca(OH)2 has low solubility. write the net ionic equation for the reaction that occurs when NaOH(aq) is mixed with Ca I2 (aq) Identify the spectator ions.

We can see that this reaction is a) a precipitation reaction, because Ca(OH)2 has a low solbuility.

First of all, write your two reactants that are given:

NaOH(aq) + CaI2(aq)

Now both NaOH and CaI2 are soluble (your teacher may or may not want you to memorize which compounds are soluble and which are not...there are rules for remembering these). There are both also ionic compounds. Since they are ionic compounds and are soluble in water, they dissociate into ions.

NaOH(aq) + CaI2(aq) --> Na+(aq) + OH-(aq) + Ca+2(aq) + 2I-(aq)

Now you know that Ca(OH)2 is not very soluble so the calcium ion and hydroxide ion, OH-, will react to form Ca(OH)2.

Na+(aq) + OH-(aq) + Ca+2(aq) + 2I-(aq) --> Ca(OH)2(aq) + Na+(aq) + 2I-(aq)

The spectator ions are the reactions that do not play a direct role in a double displacement reaction. They are the ones that are left on both sides of the equation. In this case they are the sodium ions and the iodide ions. You can cancel out the spectator ions to yield the net-ionic equation.

Ca+2(aq) + OH-(aq) --> Ca(OH)2(aq)

kaitamasaki said:
How do i know if something is positive or negative charge?

Metals form positive ions. Nonmetals form negative ions. Almost all polyatomic ions are negative. The major exception is the ammonium ion, NH4+
 
  • #3
Cesium said:
Now you know that Ca(OH)2 is not very soluble so the calcium ion and hydroxide ion, OH-, will react to form Ca(OH)2.

Na+(aq) + OH-(aq) + Ca+2(aq) + 2I-(aq) --> Ca(OH)2(aq) + Na+(aq) + 2I-(aq)

Hi,

Thanks a lot for this very meaningful and generous reply. But just one question. How do we find the spectator ions? Ca(OH)2 isn't very soluble, so does that mean its ions won't dissociate in solution and thereby, this is the way it should be written in an ionic equation?

Also, can Ionic equations only be applied to Ionic solutions and not Ionic solids?
 

1. What is a net ionic equation?

A net ionic equation is a chemical equation that only shows the species that are actually involved in the reaction. This means that spectator ions, which do not change during the reaction, are not included in the equation. Net ionic equations are used to simplify chemical reactions and better understand the actual chemical changes taking place.

2. What are ionic solids?

Ionic solids are a type of solid compound composed of positively and negatively charged ions held together by electrostatic forces. These solids have a crystalline structure and are generally brittle and have high melting points. They are often formed through the combination of a metal and a non-metal.

3. How do you write a net ionic equation?

To write a net ionic equation, first write the balanced molecular equation for the reaction. Then, determine the states of matter for each reactant and product. Next, identify and cancel out any spectator ions present on both sides of the equation. Finally, write the remaining species as the net ionic equation, showing only the species that undergo a chemical change.

4. What is the purpose of writing net ionic equations?

The purpose of writing net ionic equations is to focus on the essential chemical changes occurring in a reaction. By eliminating spectator ions, the net ionic equation allows us to better understand the reactants and products involved, and the specific chemical changes that are taking place.

5. How do ionic solids differ from covalent solids?

Ionic solids differ from covalent solids in their bonding and structure. Ionic solids are held together by strong electrostatic forces between oppositely charged ions, while covalent solids are held together by covalent bonds between atoms. Ionic solids also have a more ordered, crystalline structure, while covalent solids can have various structures such as amorphous or molecular.

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