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IN THE CHEMISTRY SECTION OF YOUR NOTEBOOK, TAKE CORNELL STYLE NOTES OVER THE INFORMATION PRESENTED IN THE FOLLOWING SLIDES. Measurements in Chemistry Aug 6, 2014

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Level Questions What is the difference between accuracy and precision? Essential Question: What are some of the things you need to know about taking measurements or expressing answers to calculations and how do we apply this knowledge? Accuracy and Precision Accuracy is how close a measured value is to the actual (true) value. Precision is how close the measured values are to each other.

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Level Questions Significant Figures: The number of significant figures in a measurement, such as 2.531, is equal to the number of digits that are known with some degree of confidence (2, 5, and 3) plus the last digit (1), which is an estimate or approximation. As we improve the sensitivity of the equipment used to make a measurement, the number of significant figures increases.

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Level questions Significant Figures Rules 1.All nonzero digits are considered significant. 2.Zeros between other nonzero digits ARE significant. 3.Zeros IN FRONT of nonzero digits are NOT significant 4.Zeros that are at the END of a number AND to the right of the decimal ARE significant. 5.Zeros at the end of the number but to the LEFT of the decimal are significant IF they have been MEASURED or are the first ESTIMATED digit; otherwise, they are not significant. a.50.3 m has ___ sig. figs. b. 3.0025 s has ___ sig. figs. c. 0.892 kg has ___ sig. figs. d. 0.0008 ms _____sf e. 57.00 g _______sf f. 2. 000 000 kg ____sf g.1000. L measured ______sf 3 5 3 1 4 7 4

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Level Questions Significant Figures: Adding and Subtracting For addition and subtraction, look at the decimal portion (i.e., to the right of the decimal point) of the numbers ONLY. Here is what to do: 1) Count the number of significant figures in the decimal portion of each number in the problem. (The digits to the left of the decimal place are not used to determine the number of decimal places in the final answer.) 2) Add or subtract in the normal fashion. 3) Round the answer to the LEAST number of places in the decimal portion of any number in the problem. Example: 5.146 + 5.29 = 10.44 You Try: a)16.5 + 9 + 5.251 = _________ b)12.944 – 2.8 = _____________ 30 10.1

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Level Questions Significant Figures: Multiplying and Dividing The following rule applies for multiplication and division: The LEAST number of significant figures in any number of the problem determines the number of significant figures in the answer Example: 2.200001 2 = 4 You Try: a)8.362 x 1.00 = __________ b)2 x 56 = ____ c)0.00043 x 4.2434 = ______ 8.37 110 0.0018

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Level Questions Scientific Notation A way of writing numbers that are too big or too small to be conveniently written in decimal form.

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Level Questions Scientific Notation

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Level Questions Scientific Notation To change any number to scientific notation, move the decimal point directly behind the very first digit, counting how many places you move. Look at these examples: 36,000 meters =3.6 x 10 4 m I moved the “understood” decimal 4 places to the left 245,000,000 buttons = 2.45 x 10 8 buttons: I moved the understood decimal 8 places to the left. 150. Grams = 1.50 x 10 2 grams: I moved the decimal 2 places to the left.. These examples are all BIG numbers (or numbers greater than one) so the exponents are positive.

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Scientific Notation You Try: 1)2.36 x 10 8 2)7.8 x 10 -3 3)3.92 x 10 -6 4)5.43 x 10 5

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