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Math is the language of science Data Analysis Ch. 2.1, 2.2, 2.3

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Problem solving in chemistry Step 2 – ANALYZE THE PROBLEM Re-read problem. What do you know? What is unknown? Make a list. Consider units, gather info from graphs, tables, figures Plan steps to take in problem solving Step 1 – THE PROBLEM Read problem. Be sure you understand what is being asked

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Problem Solving in Chemistry Step 3 – SOLVE FOR THE UNKNOWNS Determine equation needed Plug in the knowns to solve for the unknowns Solve the problem Don’t forget your conversions Step 4 – EVALUATE Think about your answer – does it make sense? Consider units – do they make sense? Check your work!

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Measurements Measurement – a quantity that has a number and a unit Qualitative vs. Quantitative measurements What’s the difference? EXAMPLES: Hot and cold – qualitative or quantitative? Temperature scale (degrees Celsius or Kelvin) – qualitative or quantitative?

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Units of Measurement Base Unit – defined unit in a system of measurement that is based on an object or an event in the physical world SI Base Units Table 2-1, p. 26

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Units of Measurement Metric use of prefixes to alter base units: Kilo (k) – 10001000 m = 1 km Deci (d) – 1/101 m = 10 dm Centi (c) – 1/1001 m = 100 cm Milli (m) – 1/1,0001 m = 1000 mm Micro (μ) – 1/1,000,0001 m = 1,000,000 μm

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Units of Measurement Derived Units – a unit that is defined by a combination of base units Volume – the space occupied by an object (cm 3 or L) Volume of an irregular object – water displacement Density – a ratio that compares the mass of an object to its volume (g/cm 3 ) Density = mass volume Practice Problems, p. 29 1, 2

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How Reliable are Measurements? Accuracy – how close a measured value is to an accepted value Precision – how close a series of measurements are to one another

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Error Error = Accepted value – Experimental value Ignore + or – signs Percent Error = l error l x 100 accepted value We use absolute value because we want the % error to be a positive value. Example p. 37: Calculate Student A’s percent error Practice: Calculate Student B’s percent error

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Scientific Notation Exponential notation is used as shorthand for writing very large or very small numbers 3.6 x 10 4 3.6 is the coefficient and 4 is the exponent (power of ten) What is the difference between 3.6 x 10 4 and 3.6 x 10 -4 ? Refer to notes in packet!

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Dimensional Analysis A CONVERSION FACTOR is a ratio of equivalent values used to express the same quantity in different units. Ex. 3 teaspoons = 1 tablespoon Conversion Factors: 3 teaspoons1 tablespoon 1 tablespoon3 teaspoons == 1 Let’s do the examples on the notes pages!

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Significant Figures Scientists indicate the precision of measurement by the number of digits they report Sig Fig Rules (VERY IMPORTANT!!!): 1. If the number has a DECIMAL: Start counting with the first non-zero (1-9) and count ALL THE WAY TO THE END. 2. If the number has NO DECIMAL: Start counting with the FIRST non-zero (1-9) and count to the LAST non-zero Let’s practice on notes pages!

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Rules for conversions 1. To convert from one unit to another, use the equivalence statement that relates the two units - a ratio of the two parts of the equivalence statement. 2. Choose the appropriate conversion factor by looking at the direction of the required change (Remember algebra class and make sure unwanted units cancel) 3. Multiply the quantity to be converted by the conversion factor to give the quantity with the desired units. 4. Check that you have the correct number of significant figures. 5. Check your work. Does your answer make sense?

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