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Understanding Accuracy, Precision, and Proportional Values in Chemistry

Learn about accuracy and precision in measurements, how to calculate error and yield percentages, and the concept of proportional values in chemistry. Explore how scientists determine measurement accuracy and the relationship between mass, volume, velocity, and time.

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Understanding Accuracy, Precision, and Proportional Values in Chemistry

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  1. Accuracy, Precision, and Proportional Values Mrs. Nielsen Chemistry

  2. Accuracy vs. Precision Accuracy: Measures how close measurements are to the correct value. Precision: Measures how close a set of measurement quantities are to one another. • High accuracy • High precision • Low accuracy • High precision • Low accuracy • Low precision • High accuracy • Low precision

  3. How can we describe a pitcher’s throws during a baseball game using accuracy and precision? Food for thought:

  4. value actual – value measured X 100 % Error = value actual mass measured % Yield = X 100 mass actual How do scientists determine the accuracy of their measurements?

  5. Mass Density = Volume constant Proportional Values 1) Directly Proportional: Question: If mass increases x2, what must happen to volume? Answer: Volume must also increase x2!

  6. x2 x2 ÷2 ÷2 So, we can say that mass and volume are directly proportional. In other words, they change by the same magnitude when density is held constant. Ex) The density of Al is 2.7 g/cm3. Finish the table below. 108.8 27.2

  7. constant Proportional Values 2) Indirectly (Inversely) Proportional: Distance = velocity x time Question: If I increase my velocity on a trip to Las Vegas, will the time it takes to get there increase or decrease? Answer: The time will decrease!

  8. Ex) If I am driving a distance of 100 miles, how long will it take me to get there if I am traveling: 25 mph? 50 mph? 100 mph? So, we can say that velocity and time are indirectly (inversely) proportional. In other words, when one value increases, the other decreases when distance is held constant. 4 hours 2 hours 1 hour

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