Law of Conservation of Mass
Essential Lab
Catalyst
1. Classify the following as an element,
compound or mixture:
a) Baking soda
b) Carbon
2. Classify each of the following as a
homogeneous or heterogeneous mixture
a) Mouthwash
b) Ice cubes in water
SWBAT apply the law of
conservation of mass to chemical
and physical changes
Agenda
• We do: Lab setup (10 min)
• You do: LoCM Essential Lab (60
min)
• I do: Law of Conservation of Mass
Mini lesson (10 min)
• You do: data analysis and
conclusion (10 min)
HOW IS MASS AFFECTED
DURING A CHEMICAL AND
PHYSICAL CHANGE?
LET’S FIND OUT!
Essential Lab
• You will be performing physical and
chemical changes on different
substances and measuring the mass
before and after the change
– Formation of a precipitate
– Crushing smarties
– Melting ice
– Baking soda and vinegar
– Dissolving sugar
– Dissolving Alka-seltzer
Conservation of Mass Lab
• You will need to write a complete lab report, with
all of the components from the ETO lab template
– Cover page
– Title
– Introduction
– Problem statement
– Hypothesis
– Materials
– Procedures (1-2 sentences for each table)
– Variables
– Data
– Data analysis
– Conclusion
Lab Setup
• Leave a space in your notebook for the
cover page, title and introduction
• Write down the problem statement,
hypothesis, materials and variable
– Problem Statement: How is the mass of
matter affected if it undergoes a physical or a
chemical change?
– Hypothesis: How do you think the mass of the
matter will be affected after the change? Will
it increase, decrease or stay the same?
WHY?
– Variables: IV, DV, Control, Constant
Lab Data and
Calculations
• Data tables (6 total)
∆𝑚
= 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑦𝑠𝑡𝑒𝑚 𝑏𝑒𝑓𝑜𝑟𝑒 𝑐ℎ𝑎𝑛𝑔𝑒
− 𝑚𝑎𝑠𝑠 𝑜𝑓 𝑠𝑦𝑠𝑡𝑒𝑚 𝑎𝑓𝑡𝑒𝑟 𝑐ℎ𝑎𝑛𝑔𝑒
∆ = ‘change in’
• Particle level representation (6 total)
• Is this a physical or a chemical change?
• How would particles look with a physical or
a chemical change?
You have 8 minutes at
each station
• USE YOUR TIME WISELY
• Lab group roles
• Project director = makes sure group is on
task and on time
• Technical manager = performs all the
measurements on the balance
• Materials manager = organizes and cleans
materials before moving to the next station
• Safety director = keeps track of time,
assists materials and project director
Lab Expectations
• You will clean the materials when you are
asked to do so
• You will rotate to the next station when you are
asked to do so
• You will not leave your station unless you are
the technical director
• You will not talk to other lab groups
• You will not prevent other groups from going to
a station because you did not use time wisely
and did not finish
LABS ARE A PRIVLEDGE
• If you are not following lab
expectations you will be given a data
sheet and asked to complete the lab
from your seat.
WHAT WERE YOUR
RESULTS? WAS YOUR
HYPOTHESIS
SUPPORTED?
Law of Conservation of Mass
Mass cannot be created
or destroyed, it can
only be converted
State the Law.
In any physical or
chemical reaction, the
total mass is conserved
or does not change.
Equation
massreactants= massproducts
Law of Conservation of Mass
Mass does not change
even if the substance
changes to a new phase.
In a Picture
Common Misconception
Other ways to say “conserved”
•
•
•
•
•
•
Saved
Keep
What goes in must come out
Reactants equal products
Remains
massreactants= massproducts
Data Analysis and
Conclusion
• Make sure you have a data table
and particle level representations for
ALL six parts
• Answer the ‘DATA ANALYSIS’ part
with complete sentences
• Answer all 7 conclusion questions
(minimum 3 paragraphs)
• Complete lab report as homework –
due next class
Extra Problem
Magnesium reacts with oxygen to produce
magnesium oxide. If 2.4g of magnesium
reacts to make 2.9g of magnesium
oxide, how many grams of oxygen
react?
Extra Problem
• Donald does a reaction in which he mixes 40
grams of sodium hydroxide with 32 grams of
another chemical. After the reaction has
completed, he is left with a precipitate that
has a mass of 18 grams. How much gas was
released in this reaction?
Another way to say mass is conserved is to
say that the mass of the reactants equals the
mass of the prodcuts
Extra Problem
50 grams of sodium reacts with chlorine to
form 126 grams of salt. How many grams of
chlorine reacted?