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Atom Inventory
Balancing Chemical Equations
Monday, February 3, 14
Chem Catalyst (left page)
Does this equation obey the law of Conservation of Mass?
Why or why not?
CuCl2(aq) + Na2S(aq) ---> CuS(s) + NaCl(aq)
Monday, February 3, 14
Rules for Balancing
Equations (notes on left page)
•
Goal: satisfy the law of conservation of matter.
•
End with equal numbers of atoms of each element on each
side of the equation.
•
You CANNOT balance by changing a subscript
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You CAN balance by changing or adding coefficients.
•
At the end, make sure the coefficient ratios are in simplest
form.
Monday, February 3, 14
Activity
• If you have any colored Legos or other snap cubes or beads,
you can use them for this activity. Otherwise, come in
during PAWS for this part and use mine.
• Print the Atom Inventory activity sheet.
• For each equation, make a key on a sheet of paper to the
element identity of each color of cube.
• Ctd next slide...
Monday, February 3, 14
Activity instructions, ctd
• Write the first equation at the top of your sheet.
• Build each compound according to its chemical formula
using the snap cubes, and place the model under its formula
in the equation.
• Follow the rules to balance the equation, remembering that
if you need more of an element, you need to add more entire
units that the element is in. For example, you can’t balance
#2 by just adding one more oxygen to the right side. You
have to add one more water to get the oxygen. This means
you need to add more units on the left side of the equation.
• Write out the final balanced equation in your lab journal.
Monday, February 3, 14
Using an Atom Inventory
•
Sometimes you don’t have cubes.
•
And some people’s brains don’t work well with
manipulatives.
•
So we have...
•
Print the practice sheet.
•
Let’s try number 2 on the practice sheet, as it is a little
harder than the ones you did with the cubes. (next slide)
Monday, February 3, 14
The Atom Inventory
Atom Inventory Example
Set up an inventory table for all the elements in the reaction,
showing the starting number of atoms for each element on
each side of the equation.
AgI +
Fe2(CO3)3 --->
FeI3 +
Reactants
Ag
I
Fe
C
O
Monday, February 3, 14
1
1
2
3
9
Ag2CO3
Products
Ag
I
Fe
C
O
2
3
1
1
3
Example, ctd
Start adding or changing coefficients to try to balance it. For each coefficient
you change, make sure to change the tally in the inventory for every element it
effects. You might need to go back & forth, changing coefficients on both
sides of the equation until you get it right. Below is what it looks like when
you are done for #2.
Monday, February 3, 14
Practice
Complete the rest of the practice sheet (as
well as the book homework) to turn in
tomorrow.
Monday, February 3, 14
Homework
•
Lesson 5: Atom Inventory
•
See Homework Sheet
Monday, February 3, 14