Unit 5
Balancing Types of Chemical Reactions
Century High School
Chemistry Instructors: Moertel, Stroh & Handlon
2013-14
Name ______
Unit 5 General Chemistry Standards
I. I can balance a chemical equation by applying the laws of conservation of mass and constant composition.
A. I can explain how the rearrangement of atoms in a chemical reaction illustrates the law of conservation of mass by placing coefficients in front of the formulas of reactants and products to balance a chemical equation.
B. I can describe a chemical reaction using words and symbolic equations by “converting” a word equation into a balanced chemical reaction or identifying the products and reactants of a chemical reaction.
II. I can explain how a chemical reaction describes a chemical change in which one or more reactants are transformed into one or more products.
A. I can classify a chemical reaction as one of these types: double replacement, single replacement, synthesis, decomposition or combustion.
B. I can use reactivity of elements to predict the products of single replacement reactions and write the balanced equation.
Background information: There are six basic types of chemical reactions that control everything in the known universe. In this lab you will explore four of them:
A. Synthesis – two elements merge into one compound.
A + B à AB Like putting together a sandwhich
B. Decomposition – compound breaks down into its components.
AB à A + B Like taking apart a lego car.
C. Single Displacement – compound gives a piece to another compound. Example:
A + BC à BA + C It’s like a “substitution” in a game. One element must substitute for another that is on the same “team”. The “teams” are metals and nonmetals.
D. Double Displacement – Compounds ‘swap’ pieces like dance couples “trading partners”.
AB + CD à CB + AD The “partners” are usually ions and a positive ion must switch with the positive ion of the other compound. Like the boys might switch partners in the dance couples
Balancing ACT
1. Determine the number of atoms of each kind in each of the following compounds with symbols.
a. CaCO3 ______
b. (NH4)2SO4 ______
c. 3H2 ______
d. 4Mg(OH)2 ______
e. Ba(NO3)2 ______
2. Count the number of atoms of each kind on each side of the following reaction. Determine if the reaction is a balanced equation. Think of the arrow à (means “reacts”) like an equal sign ( = )
The number in front of a compound or atom is the coefficient. The number down to the right of an atom is the subscript. Substances to the left of the arrow are reactants to the right products.
When balancing a reaction you may change ONLY subscripts and NOT any coefficients! Think of the formulas of each reactant and product as if they were in a “box” that you can NOT go into.
a. 2 + à 2 +
Reactants Products
______Na ______
______H ______
______O ______
b. 3 + 6 à 5 + 6
Reactants Products
______N ______
______H ______
______O ______
c. For each of the following, show the number of each type of atom on each side of the reaction. Decide if the chemical equation is balanced or not.
a. NaCl + F2 à NaF + Cl2
______Na ______
______Cl ______
______F ______
b. 3 NaBr + H3PO4 à 2 HBr + Na3PO4
______Na ______
______Br ______
______H ______
______PO4 ______
Practice: Put in the numbers in front (coefficients) in the blank if needed to balance each reaction. You do not need to write 1 if that is the coefficient. Do NOT change the formulas!
1. ___ H2 + ____ N2O2 à ____ N2 + ____ H2O
2. ____ Bi + ____ F2 à ____ BiF3
3. ____ Al + ____ Ni(NO3)2 à ____ Al(NO3)3 + ____ Ni
Balancing These Chemical Reactions:
1. _____ NI3 à _____N2 + _____I2 ______
2. _____HI à _____H2 + _____I2 ______
3. _____Al + _____O2 à _____ Al2O3 ______
4. _____K + _____S à _____K2S ______
5. _____Li + _____Cl2 à _____LiCl ______
6. _____HgO à _____Hg + _____O2 ______
7. _____Al + _____I2 à _____AlI3 ______
8. _____Al + _____S à _____Al2S3 ______
9. _____Na + _____H2O à ____H2 + ____NaOH ______
10. _____NO + _____O2 à _____NO2 ______
Lab Activity: Conservation of Mass in Reactions
Question:
When chemical reactions occur are there any changes in mass between the reactants and products? You will investigate this question by making measurements of reactants and products and using models.
Procedure Part I: Chemical Reaction of Solutions:
Take a clean, dry small beaker and mass it on the balance. Tare the mass of the beaker then add 5.0 ml of potassium iodide solution into the beaker. Record the total mass in the table. Take this off the balance
Rinse out the graduated cylinder and then measure 5.0 ml of lead (II) nitrate into it. Take a second clean, dry beaker and place this on the balance. Then add the 5.0 ml of lead (II) nitrate into it. Measure and record the mass in the table.
Now pour one solution into another. Record your observations of the two together. Then place both beakers on the balance and record their masses together.
Data Table Part I:
Solutions / Observations/ Mass of 5.0 ml
+
Empty beaker
Before (g)
/ Mass of 5.0 ml
+
Empty beakers
After (g)
Potassium
Iodide
Lead (II)
Nitrate
Both together
Mass (g) /
Procedure Part II: Chemical Reaction of Baking Soda and Acid:
Take a clean, dry small beaker and mass it on the balance. Tare the mass of the beaker then add 1.0 g of sodium bicarbonate (baking soda) formula NaHCO3 into the beaker. Record the total mass in the table. Take this off the balance
Rinse out the graduated cylinder and then measure 5.0 ml of Hydrochloric Acid (HCl) into it. Take a second clean, dry beaker and place this on the balance. Then add the 5.0 ml of Hydrochloric Acid (HCl) into it. Measure and record the mass in the table.
Now place the beaker with the baking soda on the balance. Then add the 5.0 ml of Hydrochloric Acid (HCl) solution into the beaker with the baking soda. Record your observations of the two together. Then place both beakers on the balance and record their masses together. Clean and rinse all glassware.
Data Table Part II:
Reactants / Observations/ Mass
+
Empty beaker
Before (g)
/ Mass
+
Empty beakers
After (g)
Baking soda
5.0 ml of
HCl solution
Both together
Mass (g) /
Follow up questions:
1. Describe the observations you made for Part I and for Part II that demonstrated there was a chemical reaction.
2. What was the difference between the total masses before mixing and after mixing for each Part I and II? How much was this difference?
3. Do you think the difference between the total masses before and after mixing for Part I was a “significant” amount? Was it a significant amount for Part II?
4. Why do you think there was more difference in the Part II reaction? What happened to some of the product of that reaction?
5. What does the “Law of Conservation of Matter” mean? Did each reaction provide evidence for that this law is true? Explain why one might not have shown conservation of matter.
Procedure Part III: Models of Chemical Reactions
You will now use wooden “molecular model kits” to visualize some chemical reactions and examine whether they demonstrate the Law of Conservation of Matter. Each model kit contains different colored wooden spheres with holes. The color helps represent particular atoms. The following is the color chart:
Yellow = Hydrogen Black = Carbon Green = Chlorine
Red = oxygen Blue = Nitrogen Purple = Iodine
The wood pegs or metal springs are the “chemical bonds” used to hold each atom to another.
Build each reactant in these balanced reactions and measure and record the total mass in grams. Then rearrange those same reactants into the products and record their total mass in grams. YOU MAY ONLY USE THE MATERIALS FROM THE REACTANTS MODELS TO BUILD THE PRODUCTS MODELS. Keep all materials together for the kit.
Chemical Reactions:
Mass before (g) Mass After (g)
1. 2HI à H2 + I2 ______
2. CH4 + O2 à CO2 + 2 H2O ______
3. 2 NH5 à N2 + 5 H2 ______
4. 2 N2 + Cl2 à 2 NCl3 ______
5. Cl2 + 2 HI à I2 + 2 HCl ______
6. 2 HCN + 3 O2 à CO + 2 NO2 + H2O ______
Follow up questions:
1. What can you say about the numbers and kinds of atoms of the reactants in a reaction compared to the number and kinds of atoms in the products?
2. What can you say about the total mass of all of the atoms in the reactants of a reaction compared to the total mass of all of the products?
3. Are there any “exceptions” to the Law of Conservation of Mass? If so, give examples.
Activity: Types of Chemical Reactions:
Background information: There are six basic types of chemical reactions that control every reaction in the known universe. In this activity you will explore four of them which are the ones we will emphasize in this unit. Here are the four:
A. Synthesis – two elements merge into one compound.
A + B à AB Like putting together a sandwich
B. Decomposition – compound breaks down into its components.
AB à A + B Like taking apart a lego car.
C. Single Displacement – compound gives a piece to another compound. Example:
A + BC à BA + C It’s like a “substitution” in a game. One element must substitute for another that is on the same “team”. The “teams” are metals and nonmetals.
D. Double Displacement – Compounds ‘swap’ pieces like dance couples “trading partners”.
AB + CD à CB + AD The “partners” are usually ions and a positive ion must switch with the positive ion of the other compound. Like the boys might switch partners in the dance couples.
Part I:
Your teacher will show some YouTube videos demonstrating each type of reaction. Record notes here on what you might look for to determine whether a reaction is a specific type.
Part II:
Go to back to page 5 and on the blank to the right of each reaction state the type of reaction (must be one of the four types above).
Lab Activity: Double Displacement Reactions
When a soluble ionic compound is dissolved in water it separates into the positive and the negative ions. If you mix that solution with another solution of ions you can get new combinations of positive and negative ions. Some of those new combinations might not be soluble compounds. If that happens then there is a solid formed that comes out of solution. This is called a precipitate. A precipitate might have a color (or be white). Any “cloudiness” is a precipitate.
This type of chemical reaction is called “Double Displacement” or “Double Replacement”. The positive ions of the two reactants “trade partners” much like two couples on the dance floor can “trade”.
Procedure:
In this lab activity you will mix combinations of solutions of ions, two solutions at a time. The procedure is simple. Take out a clean plastic spot plate. Add 3-4 drops of one solution to a spot. Add 3-4 drops of another solution to the same spot. Record what you see in the box of the data tables below.
Look carefully at the names of the solutions on the bottles so you have the correct ones. Be careful not to touch the tip of the dropper or bottle of one solution into a solution that is on the spot plate to avoid contamination. Always wear goggles. Also, tighten the tops on the dropper bottles when you are done. Clean and dry the spot plate with tap water.
Data Table: Copy this table in your lab.
Solutions / Barium nitrateBa(NO3)2 / Silver Nitrate
AgNO3 / Lead (II) Nitrate
Pb(NO3)2
/ Iron (III) Nitrate
Fe(NO3)3 / Copper (II) Chloride
CuCl2
Potassium Iodide KI
Sodium Hydroxide
NaOH
Potassium carbonate
Na2CO3 /
Analysis
Write balanced chemical equations for these reactions by placing coefficients as needed.
1. AgNO3 + KI à KNO3 + AgI
2. AgNO3 + NaOH à NaNO3 + AgOH
3. AgNO3 + Na2CO3 à NaNO3 + Ag2CO3
4. Ba(NO3)2 + Na2CO3 à NaNO3 + BaCO3
5. Pb(NO3)2 + KI à KNO3 + PbI2
6. Pb(NO3)2 + NaOH à NaNO3 + Pb(OH)2
7. Pb(NO3)2 + Na2CO3 à NaNO3 + PbCO3
8. Fe(NO3)3 + KI à KNO3 + FeI3
9. Fe(NO3)3 + NaOH à NaNO3 + Fe(OH)3
10. Fe(NO3)3 + Na2CO3 à NaNO3 + Fe2(CO3)3
11. CuCl2 + KI à CuI2 + KCl
12. CuCl2 + NaOH à Cu(OH)2 + NaCl
13. CuCl2 Na2CO3 à CuCO3 NaCl
Lab Activity: Single Replacement Reactions
All elements vary in their degree of “reactivity”. Some elements like those in Group VIII A (Noble Gases) do not react with anything. Other elements like potassium metal are very reactive with air and even burn in water!
In this lab you will examine some reactions of metals and try to compare the reactivity of metals within the same group as well as with metals from other groups. You will also view videos demonstrating the reactions of some nonmetals like those in Group VII A (the Halogens).