4 Summary

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Review Module 1 Material

Scientific Measurement

Accuracy:

How close a measured value is to the accepted or real value.

Precision:

The degree of reproducibility of a measured quantity; how close a series of measurements of the same quantity are to one other.

Volume:

Volume is a measure of space. It is a unit of length raised to the third power.

The SI unit of length is the meter. One meter cubed is equivalent to 1000 L. Litres, which are a convenient unit for scientific measurements, are a more common measurement unit than meters cubed.

1\ L = 1\ dm^{3}
1\ L = 1000\ mL
1\ cm^{3} = 1\ mL

Density:

A ratio of mass (m) to volume (V) of a substance.

\text{Density} = \frac{\text{mass}}{\text{volume}}

 

SI Base Units

Click on the following units of measurement to reveal their definition.
Note: Precise definitions of the SI units are not necessary to memorize. Rather, the relationships between the units and how to use them are the important parts to know.

SI Prefixes: Units of Measure for All Sizes

Multipliers that change unit values by multiples of ten.

Presenting Chemical Data

Significant Figures

An accepted method for preserving the precision of a measurement when recording data or doing calculations.

1. 2. 3. 4.
Non-zero digits are significant. Exact numbers are significant. Contained zeros are significant. Leading zeros are not significant.
5.
Trailing zeros have significance as follows:
a. b. c.
After a decimal point, significant After a non-zero number and before a decimal point, significant After a non-zero number that in not a decimal number, generally a place holder

For an even more detailed breakdown on significant figures click the link below to view.

Significant Figures

Scientific Notation

A notation for expressing large and small numbers as a small decimal between one and ten multiplied by a power of ten.

How to write using scientific notation:

1.

2.

2a.

2a.
Move the decimal point to the left or right to reach a decimal number between one and ten. Write the number obtained in step 1 multiplied by 10 raised to the number of places the decimal point was moved.

If the decimal is moved to the left, the power is positive.

Example: 140000 = 1.4 \cdot 10^{5}

If the decimal is moved to the right, the power is negative.

Example: 0.000014 = 1.4 \times 10^{-5}

 

Chemical Problem Solving Strategies

Unit Analysis and Problem Solving
A ‘book-keeping’ method for units in a calculation
Over all method of “unit analysis”:
Indicates errors in a multi-step calculation

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
Unit analysis:
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.

original quantity x conversion factor = equivalent quantity
For example converting between length units
Given that 1 meter = 39.37 inches
Conversion factors \frac{1m}{39.37inches} or \frac{39.37inches}{1m}
The same relationship, just invert as necessary to give you the units you need!

Problem Solving Examples

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

What is being asked?
What data is provided?
What do I need to know?
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

= There are 0.55 moles of oxygen atoms.
Always Check Units!

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Be Prepared! Everything you should know for 1st year Chemistry Copyright © by Andrew Vreugdenhil and Kelly Wright is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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