1. Scientific Measurement
Chapter 3
Scientific Measurement

2. Scientific Measurement
Measurement-is a quantity that has both a number and a unit
Ex. 12 inches, 5 cm
Measurements are fundamental to the experimental sciences. For that reason it is important to be able to make measurements and decide whether those measurements are correct.
Scientific notation- a given number is written as the product of two numbers: a coefficient and 10 raised to a power.
Ex. 6.9 x 105

3. Accuracy and Precision
Accuracy-is a measure of how close a measurement comes to the actual true value.
Precision- is a measure of how close a series of measurements are to one another.
To evaluate the accuracy of a measurement, the measured value must be compared to the correct value.
To evaluate precision of a measurement you must compare the values of two or more repeated measurements.

4. Scientific Measurement
Accepted value-correct value based on reliable reference
Experimental value-value actually measured in the lab.
Error- is the difference between experimental value and accepted value
Error = experimental value – accepted value

5. Percent Error
Percent error- is the absolute value of the error divided by the accepted value, multiplied by 100%
Percent error= error X 100%
accepted value

6. International System of Units (SI)
The five SI base units used by chemists are the meter, the kilogram, the Kelvin, the second, and the mole.
Table 3.1 in the book.
Common metric units of mass are the kilogram, gram, milligram, and microgram.

7. Scientific Measurements
Weight - is a force that measures the pull on a given mass by gravity.
Mass-measure of the amount of matter an object contains
Temperature is a measure of how hot or cold an object is.

8. Scientific Measurements
Scientist commonly use two equivalent units of temperature the degrees Celsius, or the degrees Kelvin
Celsius water freezes at 0 degrees and boils at 100 degrees
Kelvin- water freezes and boils
Conversions 
K=C + 273
C= K – 273 
Absolute zero – 0 point on Kelvin scale, the point at which all molecular movement stops.

9. Energy Energy-is the capacity to do work or produce heat.
The joule and the calorie are common units of energy.
1J= cal
1cal = 4.184J

10. Density Density-is the ratio of the mass of an object to it volume
Density= mass
Volume
Density is an intensive property that depends only on the composition of a substance, not on the size of the sample.
The density of a substance generally decreases as temperature increases
Why? The volume usually increases as temperature increases. Therefore, making the denominator of the density formula larger and causing the density to be smaller.