1. Accuracy, Precision, and Proportional Values
CP 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. Food for thought:
How can we describe a pitcher’s throws during a baseball game using accuracy and precision?

4. 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

5. 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!

6. 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

7. 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!

8. 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