What is the problem asking?
The volume of debris released = \(m^{3}\) = ?
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Chemical Problem Solving Strategy Theory
A 'book-keeping' method for units in a calculation
Unit analysis helps avoid errors in a multi-step calculation and provides the units for the final answer.
Over all method of “unit analysis”:
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
Unit analysis:
A method that uses a conversion factor to convert a quantity expressed in one unit to an equivalent quantity in a different unit.
Conversion factor:
States the relationship between two different units.
original quantity x conversion factor = equivalent quantity
For example converting between length units
Given that 1 meter = 39.37 inches
Conversion factors \(\frac{1\,m}{39.37 \,\text{inches}} \,\text{or} \,\frac{39.37 \,\text{inches}}{1\,m}\)
The same relationship, just invert as necessary to give you the units you need!
So to take a simple example, if we needed to convert 69.5 inches into meters we could do the following
FACT:
The more you use the “long method” of converting units, the fewer errors you will make!
How many moles of oxygen atoms are there in a 10 mL volume of water?
What is being asked?
Given a volume can you calculate a number of atoms?
What data is provided?
Data: 10 mL of water
What do I need to know?
Need to know: water is \(H_{2}O\), density of water, molecular weight of water
How do I need to state the answer?
Answer in moles of oxygen O
Convert volume of water to moles of oxygen
Calculation is: Volume of \(H_{2}O\) \(\to\) mass of \(H_{2}O\) \(\to\) mols of \(H_{2}O\) \(\to\) mols of O
= There are 0.55 moles of oxygen atoms.
Always Check Units!
Problem Set
Chemical Problem Solving Strategy Problem Set
Below are two documents. One is practice problems, the second is the same problems with solutions.
They can be downloaded and changed to suit your needs.
Click or Tap the images below to view.
Practice Problems
Problem Solutions
