Mr. Bouyer
Day 1 | Day 2 - 3 | Day 4 | Lab | Skills Test

  • Identify molecules and ions in a chemical equation.
  • Use physical state symbols in a chemical equation.
  • Identify spectator ions in a chemical equation.
  • Use the six steps to write net ionic equations.

Net Ionic Equations:
equations that attempt to show only the exact particles involved in the reaction.

 

In-class Assignment 281:
This assignment must be turned in by the end of class today to receive credit.
Scoring criterialink to a local webpage

Before beginning net ionic equations, review the difference between atoms and ions by filling in the following table:

Symbol Cr +3 Sn +2       Fe +2     S -2 Br
Protons     47 17 33   26      
Neutrons     60 18 42   30 77    
Electrons     46       23 54    
Charge       0 -3     -1    

 

Day 2 - 3

A "normal" balanced equation: 2AgNO3 (aq) + ZnCl2 (aq) 2AgCl (cr) + Zn(NO3)2 (aq)

The same equation in "net ionic form": Ag +(aq) + Cl -(aq) AgCl (cr)

You must first decide - are substances written as molecules or ions?

Molecules or Ions? Seven rules to help you decide:

1. Binary acids:

  • Strong acids are written in ionic form.
    Examples: HCl, HBr, HI
  • Weak acids are written in molecular form.
    Examples: All other binary acids.

2. Ternary acids:

  • Strong ternary acids are written as ions: the number of oxygen atoms exceeds the number of hydrogen atoms by two or more.
    Examples: H2SO4, HNO3
  • Weak ternary acids are written as molecules.
    Examples: H3PO4, HNO2

3. Polyprotic acids:

  • Those acids have more than one ionizable hydrogen.
  • The second and all other ionizations are always weak.
    Examples: H2SO4 is written in ionic form according to Rule #2. One H is removed leaving HSO4 -. Rule #3 assures us that this particle will not ionize farther.

4. Bases:

  • Hydroxides of groups 1 and 2, except Be, are strong bases and are written in ionic form.
  • All others are weak and written in molecular form.

5. Salts:

6. Oxides:

  • Oxides are always written in molecular form.

7. Gases:

  • Gases are always written in molecular form.

 

Physical state symbols in an equation
can help some with these rules.

For the equation:   H3PO4 (aq) + MnCO3 (s) Mg3(PO4)2 (cr) + CO2 (g) + H2O (l)

(aq)  indicates that H3PO4 is dissolved in water.
(s)  indicates that MnCO3 is a solid - insoluble in the water solution.
(cr)  indicates that Mg3(PO4)2 is in crystal form - insoluble in the water solution.
(g)  indicates that CO2 is a gas.
(l)  indicates that H2O is a liquid.

Based on the rules for determining molecules or ions,link to a local webpage the equation becomes:

H +(aq) + HPO4-(aq) + MnCO3 (s) Mg3(PO4)2 (cr) + CO2 (g) + H2O (l)

 

Practice Problem Set 1: Use the seven rules above to decide if each of the following should be written as a molecule or as ions in an equation. Which rule applies for each chemical?

1. zinc (II) chloride
2. magnesium phosphate
3. ammonium bromide
4. H3PO4
5. AgCl
6. HNO2
7. N2O
8. H2SO4
9. HF
10. Ba(NO3)2
11. Be(OH)2
12. O2 (g)

Practice Problem Set 2: Write each substance above as you would to begin a net ionic equation.

  • Any physical state symbols given in the original equation that still apply, such as (aq), (s), (cr), (g), or (l) are written.
  • Ions in solution are always written with the physical state symbol (aq).

 

Explore this Internet Website about Chemistry Spectator ions appear on both sides of the equation.

Steps used to write net ionic equations:

1. Using the 7 rules above link to a local webpage write each substance as molecules or ions.

2. Cancel ions that are exactly the same on both sides of the equation.

These ions would cancel: Cu+ Cu+
These ions would not cancel: Cu+ Cu+2
3. You must cancel the same number on both sides of the equation.
Before canceling the spectator ions: 4 Fe+2 6 Fe+2
After canceling the spectator ions: no iron ions 2 Fe+2
4. Cancel any other particles found on both sides of the equation.

5. Rewrite the equations in net ionic form.

6. If all coefficients are divisible by a common number, reduced them.

Sample Net Ionic Equation Problem: Write the following in net ionic form.

2AgNO3 (aq) + H2SO4 (aq) Ag2SO4 (Cr) + 2HNO3 (aq)

See the detailed solution to the problem.link to a local webpage

link to a local webpage with useful information

Practice Problem Set 3: Write these balanced equations in net ionic form.

  1. P4010 (aq) + 6H2O (l) 4H3PO4 (aq)

  2. H2SO4 (aq) H2O (l) + SO3 (aq)

  3. 3Cr(NO3)2 (aq) + CuSO4 (aq) Cu (s) + 2Cr(NO3)3 (aq) + CrSO4 (aq)

  4. MgBr2 (aq) + Cl2 (g) MgCl2 (aq) + Br2 (l)

  5. Al(NO3)3 (aq) + 3NaOH (aq) Al(OH)3 (cr) + 3NaNO3 (aq)

  6. (NH4)2S (aq) + Fe(NO3)2 (aq) 2NH4NO3 (aq) + FeS (cr)

  7. 4CuCNS (cr) + 7KIO3 (aq) + 14HCl (aq) 4HCN (aq) + 4CuSO4 (aq) + 7ICl (cr) + 7KCl (aq) + 5H2O (l)

Research Links:

Chemistry Class

 

 

 

 

 

 

 

 

Practice Problem Set 1 Answers:
1. ions - rule 5
2. molecule - rule 5
3. ions - rule 5
4. molecule - rule 2
5. molecule - rule 5
6. molecule - rule 2 		7. molecule - rule 6
8. ions - rule 2 (rule 3 will also apply)
9. molecule - rule 1
10. ions - rule 5
11. molecule - rule 4 or rule 5
12. molecule - rule 7

 

 

 

 

 

 

 

 

Practice Problem Set 2 Answers:
1. Zn+2(aq) + 2Cl -(aq)

2. Mg3(PO4)2

3. NH4+(aq) + Br -(aq)

4. H3PO4

5. AgCl

6. HNO2

7. N2O

8. H +(aq) + HSO4-(aq)

9. HF

10. Ba+2(aq) + 2NO3-(aq)

11. Be(OH)2

12. O2 (g)