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Chemical Reactions:
Mass Relationships
Some assumptions I am making:
You:
•
can differentiate between an
atom
and a
molecule
given a picture or a formula
•
know
the implications of atomic weight
(or mass) of an element.
•
can enumerate the # of protons, and #
electrons for any elementgiven the
name or symbol of the element.
Chemical Reactions:
Mass Relationships
Some assumptions I am making:
•
You can define and give an example of
a mole of a substancegiven the
formula
.
•
You can calculate the mass of 1 mol of
a substance or 1 molecule of a
substancegiven the formula.
Chemical Reactions:
Mass Relationships
Some assumptions I am making:
•
Given a formula, you can calculate
a % composition.
Let’s see what you can do now!
What is the %C in Calcium
carbonate (CaCO
3
)?
Chemical Reactions:
Mass Relationships
Some assumptions I am making:
•
Given mass data, you can determine an
empirical formula.
•
A substance contains: 2.0g of Ca,1.2g
of C, and 4.8g of O. What is the
empirical formula of the substance?
•
You know the difference between an
empirical and molecular formula.
So what should you do?
•
Be certain to try problems of
this sort!!
•
I won’t hesitate to ask, and I
won’t spend time in class going
over these concepts.
Chemical Reactions:
Mass Relationships in Reactions
A.Equations
1. Reactant(s) > Product(s)
2. IMPORTANT!!! The number of atoms of
each element on both sides of the arrow must be
equal.
3. Formulas of reactants and products are
fixed!
4. To achieve atomic balance we can adjust only
the COEFFICIENTS.
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A.Equations
4. To achieve atomic balance we can adjust only
the COEFFICIENTS.
x
A +
y
B >
z
C +
w
D
Chemical Reactions:
Mass Relationships in Reactions
B. Mechanics
1. Balance atoms of "most complex"
substance first.
2. Leave atoms/molecules of elements till
later.
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 Spring '09
 Warren
 Mole, Molecule

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