# Balancing Chemical Equations

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Chapter 3 Homework

Due: 11:59pm on Tuesday, September 22, 2009

Balancing Chemical Equations

Learning Goal: To learn to balance chemical equations by inspection.

According to the law of conservation of mass, matter cannot be created or destroyed. Therefore, a chemical equation must show the same number of each kind of atom in the reactants as it does in the products. As shown in the figure, the balanced equation has 6 atoms of hydrogen and 2 atoms of nitrogen on each side of the arrow.

One is often presented with unbalanced chemical equations for which one must supply the coefficients.

The following equation is not balanced:

Part A

Notice that " " appears in two different places in this chemical equation. is a polyatomic ion called "sulfate." What number should be placed in front of to give the same total number of sulfate ions on each side of the equation?

Hint A.1 Confused by parentheses?

Parentheses surrounding a set of elements means that the subscript applies to all the atoms within the parentheses. For example: the compound contains two aluminum atoms and three sulfate ions (12 oxygen atoms, 3 sulfur atoms).

Correct

Part B

Now that we have put a coefficient of 3 in front of , what coefficient should go in front of to balance calcium ( )?

Hint B.1 Count the number of calcium atoms on the left

Hint not displayed

Correct

By placing a coefficient of 3 in front of calcium chloride, we have indicated three calcium atoms on the right to match the three calcium ions on the left:

Part C

Now that we have put coefficients of 3 in front of and , what coefficient should go in front of to balance both the atoms and the atoms?

Correct

There are now 6 chlorine atoms, and 2 aluminum atoms on each side of the equation. The final balanced equation looks like this:

Ionic Compound Nomenclature and Formulas

Learning Goal: To learn to write the systematic name of ionic compounds given the chemical formula and to write the chemical formula given the systematic name.

Ionic bonds form when one atom completely transfers one or more electrons to another atom, resulting in the formation of ions. Positively charged ions (cations) are strongly attracted to negatively charged ions (anions) by electrical forces. All chemical compounds can be named systematically by following a series of rules. Binary ionic compounds are named by identifying first the positive ion and then the negative ion. Naming compounds with polyatomic ions involves memorizing the names and formulas of the most common ones.

Part A

Give the systematic name for the compound .

Hint A.1 How to approach the problem

When naming ionic compounds, the cation is identified first and the anion is identified second.

Hint A.2 Name the anion

What is the name of the polyatomic anion ?

Hint A.2.1 Naming polyatomic ions

Hint not displayed

Correct

Correct

Aluminum is a metal that has only one oxidation state. Therefore it is not necessary to write III in parentheses in the systematic name. Only those metals with more than one oxidation state must have its state written in the name.

Part B

Give the systematic name for the compound .

Hint B.1 How to approach the problem

Hint not displayed

Hint B.2 Name the anion

Hint not displayed

Hint B.3 Determine the oxidation number

Hint not displayed

Correct

Although it seems like a small difference, iron(II) and iron(III) behave much differently chemically. They even form different-colored compounds because of the number of electrons they have to bond. Therefore it is very important to specify which oxidation state is being used.

Part C

Write the formula for the compound magnesium oxide.

Hint C.1 How to approach the problem

Use the periodic table to determine the charge for each ion. Because this is a neutral ionic compound, the positive charges must equal the negative charges. Reduce the subscript on each ion to its lowest whole number ratio.

Hint C.2 Determine the charge of the anion

What is the charge of the oxide ion?

Hint C.2.1 Group 16 elements

Hint not displayed

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