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Types of Observations and Applications of scientific Notation | CH 100, Study notes of Chemistry

Material Type: Notes; Class: Fundamentals for Chemistry; Subject: Chemistry; University: Portland Community College; Term: Unknown 1989;

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Ch 100: Fundamentals for Chemistry
Chapter 2: Measurements & Calculations
Lecture Notes
Types of Observations
Qualitative
Descriptive/subjective in nature
Detail qualities such as color, taste, etc.
Example: “It is really warm outside today”
Quantitative
Described by a number and a unit (an accepted reference scale)
Also known as measurements
Notes on Measurements:
Described with a value (number) & a unit (reference scale)
Both the value and unit are of equal importance!!
The value indicates a measurement’s size (based on its unit)
The unit indicates a measurement’s relationship to other physical
quantities
Example: “The temperature is 85
o
F outside today”
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Ch 100: Fundamentals for Chemistry

Chapter 2: Measurements & Calculations Lecture Notes

Types of Observations

  • Qualitative
    • Descriptive/subjective in nature
    • Detail qualities such as color, taste, etc. Example: “It is really warm outside today”
  • Quantitative
    • Described by a number and a unit (an accepted reference scale)
    • Also known as measurements
  • Notes on Measurements:
    • Described with a value (number) & a unit (reference scale)
    • Both the value and unit are of equal importance!!
    • The value indicates a measurement’s size (based on its unit)
    • The unit indicates a measurement’s relationship to other physical quantities Example: “The temperature is 85oF outside today”

Application of Scientific Notation

Writing numbers in Scientific Notation 1 Locate the Decimal Point 2 Move the decimal point to the right of the non-zero digit in the largest place

  • The new number is now between 1 and 10 3 Multiply the new number by 10 n
  • where n is the number of places you moved the decimal point 4 Determine the sign on the exponent, n
  • If the decimal point was moved left, n is +
  • If the decimal point was moved right, n is
  • If the decimal point was not moved, n is 0 Writing Scientific Notation numbers in Conventional form 1 Determine the sign of n of 10 n
  • If n is + the decimal point will move to the right
  • If n is – the decimal point will move to the left 2 Determine the value of the exponent of 10
  • Tells the number of places to move the decimal point 3 Move the decimal point and rewrite the number

Measurement Systems

There are 3 standard unit systems we will focus on:

  1. United States Customary System (USCS)
    • formerly the British system of measurement
    • Used in US, Albania, and a couple other countries
    • Base units are defined but seem arbitrary (e.g. there are 12 inches in 1 foot)
  2. Metric
    • Used by most countries
    • Developed in France during Napoleon’s reign
    • Units are related by powers of 10 (e.g. there are 1000 meters in 1 kilometer)
  3. SI (L’Systeme Internationale)
    • a sub-set set of metric units
    • Used by scientists and most science textbooks
    • Not always the most practical unit system for lab work

Rules for Counting Significant Figures

  • Nonzero integers are always significant
  • Zeros
    • Leading zeros never count as significant figures
    • Captive zeros are always significant
    • Trailing zeros are significant if the number has a decimal point
  • Exact numbers have an unlimited number of significant figures

Rules for Rounding Off

  • If the digit to be removed is
    1. less than 5, the preceding digit stays the same
    2. equal to or greater than 5, the preceding digit is increased by 1
  • In a series of calculations, carry the extra digits to the final result and then round off
  • Don’t forget to add place-holding zeros if necessary to keep value the same!!

Exact Numbers

Exact Numbers are numbers that are assumed to have unlimited number of significant figures are considered to be known with “absolute” certainty. You do not need to consider or count significant figures for exact numbers. The following are considered exact numbers for CH100:

  1. Counting numbers, such as:
    • The number of sides on a square
    • The number of apples on a desktop
  2. Defined numbers such as those used for conversion factors, such as:
    • 100 cm = 1 m, 12 in = 1 ft, 1 in = 2.54 cm
    • 1 kg = 1000 g, 1 LB = 16 oz
    • 1000 mL = 1 L; 1 gal = 4 qts.
    • 1 minute = 60 seconds
  3. Numbers or constants defined in equations, such as:
    • y = 3x + 15 (both the “3” and the “15” are exact numbers)

Converting between Unit Systems

  • Converting units from one unit system to another (especially within the Metric system) can appear daunting at first glance. However, with a little guidance, and a lot of practice, you can develop the necessary skill set to master this process.
  • To begin, here is a simple mnemonic to guide you through the unit conversion process: 1. Eliminate 2. Replace 3. Relate
  • All unit conversions, regardless of how complex they appear, involve these 3 simple steps. In the following sections, you will be stepped through the unit conversion process using these 3 words as a guide.

Example: Unit Conversion

  1. Convert 25.0 m to cm
  2. Convert 1.26 g to kg

Temperature of ice water and boiling water.

Unit Conversion & Temperature Scales

Unit conversion involving temperature is tricky since the “zero” value for each scale is different and thus requires accounting for this “offset” between the various scales. At 0oC, the Kelvin scale has a 273.15 unit “head start” and the Fahrenheit scale has a 32 unit head start

  1. The temperature span between the freezing and boiling points of water reveal the relation between the temperature scale increments: 100 oC = 100K = 180oF
  2. However, the zero points are different as evident for the freezing point for water: 0 oC = 273.15K = 32oF
  3. The relations between the temperature scales:

a. Celsius to Fahrenheit:

b. Celsius to Kelvin:

o o

o o F C o

180 F T T + 32 F 100 C

  = (^)    

K oC o

100K T T + 273.15K 100 C

  = (^)    

Mass

  1. Mass is the quantity of matter in a substance
  2. Mass is measured in units of grams
  3. Mass does not reflect how much volume something has
  4. The kilogram (kg) unit is the preferred unit of mass in the SI

system. a. 1 kilogram is equal to the mass of a platinum-iridium cylinder kept in a vault at Sevres, France. b. 1 kg has the weight equivalent (on Earth) of 2.205 lb

Conservation of Mass: The total quantity of mass is never

created nor destroyed during a chemical process

Distinguishing Mass vs. Weight

  1. Mass is a fundamental property of matter, it is the amount of “stuff” in an object
  2. Mass represents an object’s inertia (tendency to resist change in motion)
  3. Mass is the same everywhere in the universe
  4. SI Units of mass are kilograms (kg) 1. Weight is the effect (or force) of gravity on an object’s mass 2. Weight depends on location (& local gravity) 3. Weight is not a fundamental property of matter 4. SI units of weight are newtons (N) 5. USCS units are pounds (lb)
  • The terms mass and weight are commonly used interchangeably but they are fundamentally different!
  • The following are some important differences between mass and weight:

Manipulating the Density Equation

Mass

Density

Volume

Mass

Volume

Density

Mass = Density × Volume

mass

density volume