Accuracy, Precision, and Proportional Values CP Chemistry

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

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

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

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

So, we can say that mass and volume are directly proportional 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. Density (g/cm3) Mass (g) Volume (cm3) 2.7 54.4 20.1 40.2 10.05 ÷2 ÷2 x2 x2 108.8 27.2

Proportional Values 2) Indirectly (Inversely) Proportional: Distance = velocity x time constant 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!

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. 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? 4 hours 2 hours 1 hour