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1.4: Summary

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    The original version of this chapter contained H5P content. You may want to remove or replace this element.

    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.

    The original version of this chapter contained H5P content. You may want to remove or replace this element.

    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.

    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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