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Lab 8: Chemical Reactions
Part I: Law of Conservation of Mass
Introduction:
Chemical reactions involve two or more chemical compounds reacting to form different
compounds. In a chemical reaction the molecules or compounds that exist before the reaction is started
are referred to as the reactants. The compounds formed through the reaction are known as the
products. The reactants and changed into the products through a chemical reaction.
Reactants  Products
There are a number of types of reactions that can exist. Each category of reaction is
characterized by the types and amounts of reactants and/or products.
Therefore during chemical reactions the amount of matter started with must be the amount of
matter ended with. Matter and mass can never be created or destroyed. Instead matter is simply
rearranged into different forms. In order for a chemical reaction to be balanced the mass of the
reactants and the mass of the products must be the same. Likewise according to the Law of
Conservation of Matter then number of atoms that are present before a reaction must be equal to the
number of atoms formed in the products.
Problem: Is mass conserved in a reaction of barium nitrate with potassium sulfate to yield
potassium nitrate and barium sulfate? The reaction being performed today is a type of reaction
known as a double replacement reaction where two compounds rearrange to form two new
compounds.
Ba(NO3)2(aq) + K2SO4(aq) ---- > 2KNO3(aq) + BaSO4(s)
Hypothesis: What relationship should the mass of reactants have to the mass of the products?
Materials and Methods:
1. Measure the mass of an empty dry 50mL and 100mL beaker using the quadruple beam balance.
2. Obtain and expel a full pipette of Ba(NO3)2(aq) into the 50mL beaker. Record the new mass and
determine the mass of just the Ba(NO3)2(aq).
3. Place a full pipette of K2SO4(aq) into the 100mL beaker. Record the new mass of the beaker and
determine the mass of K2SO4(aq).
4. Carefully pour the Ba(NO3)2(aq) into the 100mL beaker in order to react it with the K2SO4(aq) and
swirl.
5. Once the reaction has been observed, record any obvious changes or indicators that a chemical
reaction has taken place. Measure the mass of the 100mL beaker again with the new products
and determine the mass of just the products.
Results:
Mass of
50mL
beaker
(empty)
Mass of
100mL
beaker
(empty)
Mass of
50mL
beaker
with
Ba(NO3)2
Mass of
Ba(NO3)2
Mass of
100mL
beaker
with
K2SO4
Mass of
K2SO4
Total
Mass of
reactants
Mass of
beaker
and
products
Mass of
products
Part II: Indicators of Chemical Change
Indicators of Chemical Change
A. To identify when a chemical change has occurred one of four possible things will be observed:
1. Change in Physical properties
2. Creation of a precipitate
3. Release of gas
4. Absorption or release of heat
B. For the following 7 solutions identify any and all physical properties and list them in the space
provided. Once all the solutions have been observed you will be creating a mixture of all
possible combinations. In the well plate provided add 4 drops of the first solution and then add
four drops of the second solution. Record any changes that you may observe in the space
provided. Once you have mixed each pair of liquids decide if a chemical change has occurred.
Solution Number
1
2
3
4
5
6
7
Name of Solution
Physical Properties
(color, odor, viscosity)
Solutions being mixed
Observation
Solutions being mixed
1+2
3+4
1+3
3+5
1+4
3+6
1+5
3+7
1+6
4+5
1+7
4+6
2+3
4+7
2+4
5+6
2+5
5+7
2+6
6+7
Observations
2+7
C. Once you are done, you will be provided with an unknown liquid. This liquid is one of the seven
you examined. It is your job to identify which substance it is based on its physical and chemical
properties.
Physical Properties of Unknown:
Solutions being mixed
Unknown + 1
Unknown + 2
Unknown + 3
Unknown + 4
Unknown + 5
Unknown + 6
Unknown + 7
D. Identity of Unknown and Reasoning:
Observations