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Chemistry UNIT 1

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Susie Smith August, 2010 Chemistry is the study of matter.

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Scientific Method A logical method of problem solving.

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Steps of the Scientific Method Making observations that lead to a question. Forming a hypothesis to answer the question. Testing the hypothesis by experimentation. Making a conclusion based on the results.

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Definitions Observation- use of senses and devices in the lab to obtain information. Conclusion- a statement based on observations and prior knowledge.

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Types of observations Quantitative- includes numbers and units. Qualitative- does not include numbers and units. Examples-

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Hypothesis- an educated guess Explains an observation. Can be tested. Will predict an outcome. Must be written as a statement.

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Experiment Designed to test an hypothesis. Involves variables Is performed under controlled conditions.

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Variables Variables are factors that can be changed. – Control variable is a variable that is held constant. – Manipulated or independent variable is changed by the scientist. – Responding or dependent variable changes as a result of the experiment.

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International System (SI) Measuring system used in science (also called the MKS)

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Length Distance between two points Base Unit- Meter (m) Instrument- meter stick or metric ruler

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Mass Amount of matter in a substance Base Unit- gram SI Unit – kilogram Instrument- triple-beam balance

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Volume Amount of space an object occupies Base Unit- liter (L) Instrument- metric ruler or graduated cylinder

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Time Interval between two occurances Base Unit- second (s) Instrument- stop watch

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Temperature Average kinetic energy Base Unit- Celsius ( o C) or Kelvin (K) Instrument- thermometer.

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Scientific Notation Numbers are expressed in this form: M X 10 n M is a number between 1 and less than 10. And n is equal to an exponent.

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How to take numbers out of scientific notation 1 X 10 3 = 1000 Positive exponents move the decimal place to the right n spaces. 1 X 10 -3 =.001 Negative exponents move the decimal place to the left n spaces.

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Scientific Notation 6.2 X 10 4 1.5 X 10 -2 2.4 X 10 -5 7.06 X 10 6 6.0 X 10 6

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How to put numbers into Scientific Notation 6,011,000 0.058 24 0.009009 6.734114

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Conversion Factors One large unit = how many smaller units. One dozen = 12 units.

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Common Conversions “ PrefixAbbreviationConversion fact MegaM1Mm = 1,000,000 m Kilo k1km = 1,000 m Deci d1m= 10dm Centi c1m= 100cm Milli m1m= 1,000 mm Micro 1m= 1,000,000 m

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Conversions Start every problem with the original amount. Then use a conversion fact to convert the units of measurement to what you need. Set up every problem as a fraction with the unit you are looking for on top and the unit you started with on bottom.

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Practice Problems 1 kg = ________ g 1s = _________ ds ________ = 1 L ______ dollars = 100 centidollars 100 dg = _____ g

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How to work your calculator? Look for EE, X10, or ^ keys on your calculator Every calculator is different. Make notes about how to use your calculator.

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Practice Convert 152 cm to m. Use the conversion fact 1m = 100cm 152 cm X 1m = 1.52 m 100 cm

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Conversion Practice Convert 62 kg to _________ g. Convert 1700 m to _______ m Convert 0.0056 mm to ______km.

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Conversions with Derived Units Convert 570 g/L= __________ g/mL 16 m/min = ______________ m/s Convert 65 km/h =____________ m/s

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Order of operations Please Excuse My Dear Aunt Sally. Parenthesis Exponents Multiply or Divide Addition or Subtraction

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Definitions Accuracy- closeness of a measurement to the accepted value Precision- the reproducibility of a measurement

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Significant Digits All measured digits plus 1 estimated digit Read the smallest division on the instrument and then estimate one more digit 3.21 cm, _____ significant digits, ____ measured and ___ is estimated.

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Zeros and significant digits Zeros are placeholders. They are only significant if they are in between two non zero numbers. 906 They are significant if they follow a non zero number and are after a decimal. 15.00 They are not significant if they are before a decimal and before a non zero number. 0.0015 They are significant if a bar is placed on top of the 0.

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Rules for rounding After multiplying or dividing – Round to the least number of significant digits – Round to the weakest link. – Ex. 420 X 100 = _________

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Rounding After adding and subtracting, – Round answer to 1 st column containing an estimated digit – Round to the weakest column 12.001 4.02 + 3 19.021 19

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Rule of 5’s When a number is exactly half way between two numbers, always round to the even number. 12.5 rounds to 12 11.5 rounds to 12 12.5001 rounds to 13

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Scientific Method Variable- a physical quantity which can change in the experiment In a good experiment, only one variable is allowed to change.

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Parts of an Experiment Manipulated (independent) variable- is changed by the experimentor Responding (dependent) variable- depends on the results of the experiment Control variables- are variables that are held constant on each group.

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Weight verses Mass On the moon, your mass would not change, and your weight would change. Mass- is the amount of matter an object has – kilograms Weight- is the affect of gravity pulling on an object – Newtons

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Scientific Method Question Hypothesis Research Experimentation Conclusion Retest

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Graphing scientific data X axis- independent variable Y axis- dependent variable means “is directly proportional to”

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Straight Line Graph y x y = kx, where k is a constant Slope is y/x or rise/run

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Inverse proportion y 1/x y = k/x Graph is a hyperbola

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Equations When the variables of an equation are on the same side of the equal sign, the variables are inversely proportional. When the variables of an equation are on opposite sides of the equal sign, the variables are directly proportional. P A = F

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