Naming Ionic Hydrates - Online Tutor, Practice Problems & Exam Prep

Naming Ionic Hydrates

In these series of videos, we'll learn what ionic hydrates are and the rules needed to name them. Now we're going to say ionic hydrates are simply ionic compounds linked to at least one molecule of water. Here we have as our example Cu_xH₂O. X just represents some unknown number of water molecules that are linked to copper and in chlorine together here. Now the dot here is what's referring to as the linking or bonding of the water molecules to this ionic compound. Now that we know what an ionic hydrate is, let's look at the rules to name them. Some of these rules are pretty familiar to us because a big chunk of it has to do with naming ionic compounds, which we've covered in earlier videos. Now steps 0 to 3 are the same rules as naming ionic compounds. If you don't remember those rules, make sure you go back and take a look at our videos on naming ionic compounds. Step 4 is new. For step 4, we're going to say that the water portion will be called hydrate, but we also have to specify how many of these hydrates are connected to my ionic compound. We're going to say to describe the number of water molecules in a hydrate, we now use numerical prefixes. Now these numerical prefixes go from mono to deca, mono meaning 1, and then di is 2, tri is 3, tetra is 4. Some of these terms we are familiar with. Pentagon has 5 sides, so penta has 5. Hexagon has 6 sides. Hepta, we may not have been familiar with that because that's not a term that you usually see. So hepta is 7. Octagon, 8. Now nona is 9, and deca is 10. So now that we know how to identify ionic hydrates and we've learned the basic rules for naming them, let's take a look at some questions and put what we learned into practice.

Naming Ionic Hydrates Example 1

In this example question, we're told to name the following ionic hydrate. Alright. So let's do the easy part first. We have 5 water molecules here. So 5 would mean that we're using the numerical prefix of penta, and the water would be called hydrate. So this is pentahydrate. Now, if we take a look at the ionic compound portion, we have lead with oxygen. With lead, we have an issue though. Lead can have a charge of either 2+ or 4+. Remember, lead is not a transition metal, but it and tin have this issue where they can be 2+ or 4+. If you don't remember that, again, go back and take a look at my periodic table videos that deal with charges. Now here, oxygen is in group 6A. And remember, if you're in group 6A, your charge is -2. So let's think about this. Oxygen is -2, there are 2 oxygens within the formula. So collectively, the oxygens together are -4. For PbO₂ to be neutral, this -4 has to be counterbalanced or canceled out by what? By a +4. So the +4 of lead cancels out the -4 from the 2 oxygens, thereby giving us a neutral ionic compound. So that would mean that we're dealing with, for our ionic compound, lead(IV), remember, it uses Roman numerals because it has multiple charges, lead(IV) oxide pentahydrate. So this one was tricky, but this would be the name of our ionic hydrate.

Give the systematic name from the given formula:K₂Cr₂O₇ ∙ 3 H₂O

• A. dipotassium dichromate trihydrate
• B. potassium dichromate trihydrate
• C. potassium chromate trihydrate
• D. trihydrate potassium chromate

Write the chemical formula for the following compound:Calcium selenide hexahydrate

• A. CaSe • 6 H₂O
• B. CaSe₂ • 6 H₂O
• C. Ca₂Se • 6 H₂O
• D. Ca₂Se₂ • 6 H₂O
• E. Ca₃Se₂ • 6 H₂O

Here’s what students ask on this topic:

What are ionic hydrates and how are they represented?

Ionic hydrates are ionic compounds that are associated with water molecules. They are represented in the form CuxH2O, where 'Cu' stands for the ionic compound, and 'x' indicates the number of water molecules attached to it. The dot (·) in the formula signifies the linkage between the ionic compound and the water molecules. For example, CuSO4·5H2O represents copper(II) sulfate pentahydrate, indicating that five water molecules are associated with each formula unit of copper(II) sulfate.

What are the steps to name ionic hydrates?

To name ionic hydrates, follow these steps:
1. Name the ionic compound as you normally would.
2. Identify the number of water molecules associated with the compound.
3. Use the appropriate numerical prefix to indicate the number of water molecules: mono (1), di (2), tri (3), tetra (4), penta (5), hexa (6), hepta (7), octa (8), nona (9), and deca (10).
4. Add the word 'hydrate' after the numerical prefix. For example, CuSO4·5H2O is named copper(II) sulfate pentahydrate.

What is the significance of the dot in the formula of an ionic hydrate?

The dot (·) in the formula of an ionic hydrate signifies the linkage or association between the ionic compound and the water molecules. It indicates that the water molecules are not part of the ionic compound's primary structure but are instead loosely bonded to it. For example, in CuSO4·5H2O, the dot shows that five water molecules are associated with each formula unit of copper(II) sulfate.

How do you determine the number of water molecules in an ionic hydrate?

The number of water molecules in an ionic hydrate is determined by the subscript 'x' in the formula CuxH2O. This subscript indicates how many water molecules are associated with each formula unit of the ionic compound. For example, in the formula CuSO4·5H2O, the subscript '5' indicates that there are five water molecules associated with each formula unit of copper(II) sulfate.

What are the numerical prefixes used in naming ionic hydrates?

The numerical prefixes used in naming ionic hydrates are: mono (1), di (2), tri (3), tetra (4), penta (5), hexa (6), hepta (7), octa (8), nona (9), and deca (10). These prefixes are used to specify the number of water molecules associated with the ionic compound. For example, CuSO4·5H2O is named copper(II) sulfate pentahydrate, where 'penta' indicates five water molecules.