# Take the Test

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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.

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##### SI Prefixes: Units of Measure for All Sizes

Multipliers that change unit values by multiples of ten.

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## 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.

##### 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

##### 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 *

##### 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?

##### 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!