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Slide 2 Chemistry Unit 2: Scientific Measurement Salisbury High School Spring 2007 Slide 3 Chemistry February 12, 2007 1) Begin Unit on Measurements 2) Notes on measurements, accuracy, precision 3) HW: WS 2.1 Slide 4 Measurements Opening Questions Questions: 1. What is the purpose of a measurement? 2. Why are measurements important to science? Slide 5 Measurements Measurements are fundamental to science Measurements may be: a. Qualitative b. Quantitative Slide 6 Measurements Qualitative Measurement : is a non-numerical measurement Example: The solution turned brown when ammonia was added to iron (III) chloride Slide 7 Quantitative Measurements Quantitative Measurements: consist of two parts a. A number b. A scale (or unit) Slide 8 Quantitative Measurements Example: The rock has a mass of 9 kg Scale (unit) Number Slide 9 Practice: Classify as qualitative or quantitative 1. Water is a liquid 2. The temperature was 9C. 3. The book is 12 cm long 4. The mixture contains 5 blue marbles and 12 g of red clay Slide 10 Terms Used for Measurements In comparing scientific results, the following terms are applied: a. accuracy b. precision Slide 11 Accuracy Accuracy refers to the agreement of one experimental result to the true or accepted value The closer the value is to the true value, the more accurate one is Slide 12 Accuracy Examples of accuracy: kicking a soccer goal hitting a three point shot determining the value of to be 3.13 Slide 13 Practice: Tell if the accuracy is good or poor a. Finding the percent H 2 O 2 to be 2.9% (the bottle says it contains 3%) b. Finding that a 2 Liter bottle only contains 1.5 Liters of soda c. Filling a 1000 mL volumetric flask with 1050 mL of water Slide 14 Precision Precision refers to how close several different experimental values are to each other Slide 15 Precision Examples: Scoring three goals in a soccer game Shooting an air ball five times Finding the value for to be 3.12, 3.15, 3.13 Slide 16 Precision and Accuracy Problems Precision problems usually arise from the skill of the person doing the experiment or the division of the measuring instruments Slide 17 Precision and Accuracy Problems Accuracy problems usually related to the quality of the equipment used to make measurements Precision relates to how consistent the results are; accuracy relates to how correct the results are Slide 18 Describe the accuracy and precision of the following A student makes the following grades: a. 99, 100, 98, 100 b. 45, 43, 44, 42 c. 100, 23, 60, 89 Slide 19 Scientific Notation Occasionally some measurements are really small or exceptionally large 1, 400, 000 km, the distance to the sun 0.000 000 000 066 7, the Universal Gravitation Constant To help you use these, you may express them in scientific notation Slide 20 Scientific Notation Continued In scientific notation, a number is written as the products of two numbers: a coefficient and some power of 10 Slide 21 Scientific Notation Continued The general form for scientific notation is: M x 10 n where M is 1 but < 10 n is an integer and exponent {integers must be a positive or negative whole number} Slide 22