# 1.3: Chemical Problem Solving Strategies A YouTube element has been excluded from this version of the text. You can view it online here: http://pb.libretexts.org/chem12/?p=42

# Unit Analysis and Problem Solving

##### Over all method of “unit analysis”:
Unit analysis helps avoid errors in a multi-step calculation and provides the units for the final answer.

1) Write the units with every number you include in a series of calculations

2) String your calculations together as a series of multiplications or divisions before doing any math

3) Cancel your units to see the calculation evolve
* Gives you a hint about the next step *

### Calculations: Converting from One Unit to Another

##### Conversion factor:

A method that uses a conversion factor to convert a quantity expressed in one unit to an equivalent quantity in a different unit.

States the relationship between two different units.

# Calculations: Using Unit Analysis ##### FACT:

The more you use the “long method” of converting units, the fewer errors you will make!

# Problem Solving Examples

#### How many moles of oxygen atoms are there in a 10 mL volume of water?

##### How do I need to state the answer?
Given a volume can you calculate a number of atoms? Data: 10 mL of water Need to know: water is $H_{2}O$, “> density of water, molecular weight of water Answer in moles of oxygen O

### Convert volume of water to moles of oxygen

Calculation is: Volume of $H_{2}O \rightarrow$ mass of $H_{2}O \rightarrow$ mols of $H_{2}O \rightarrow$ mols of $O$ ## Examples

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### Quiz

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