Properties of matter are either:

• Qualitative - properties described without measurements, such as color, odor, and texture.
• Quantitative - properties that are measured and described by a number of standard units, such as mass and volume.

Significant digits:

• A significant digit is one which is actually measured.
• The number of significant digits in a measurement depends on the ability of the measuring device.

  When a calculation involves measurements with different numbers of significant digits, the answer should have the same number of significant digits as the least in the measurements.

Practice problems:

1. A soil sample, as received by a laboratory, weighed 5.6165 g. After drying in an oven, this same sample weighed 2.7749 g. What is the percentage of moisture in the sample?

2. Determine the number of significant digits in each of these:
   1. 6.751 g
   2. 0.157 kg
   3. 28.0 ml
   4. 2500 m
   5. 0.070 g
   6. 30.07 g
   7. 0.0067 cm
   8. 6.02 x 10²³ atoms

      

Some chemistry classes place a high priority on using significant digits in calculations. They are useful when rounding off the final answer in claculations. This chemistry class places more importance on using the overall process than the minute details. All calculations this year will be evaluated based on your understanding of the concept. You may round off final answers liberally. The information on this page is enough for Howe High School Students.

Uncertainty in measurement:

• No matter the measuring tool, there will always be some uncertainty in the measurement. Both the tool and the observer have add their own uncertainty to the measurement.
• Use this tutorial to become familiar with measurement uncertainty.

Reliability of measurement:

• Accuracy - refers to how close a measurement is to the true value of the quantity.
• Precision - refers to how close a set of measurements for a quantity are to one another, regardless of whether they are correct.

Experimental error - the comparison of an experimental value to a known value. We will use this calcuation to determine how well you did your experimental measurements.

1. An experiment produces data indicating that the formula mass of water is 16 amu. The formula mass of water is known to be 18 amu. What percent of error occured in this experiment?
2. A laboratory scale measures the mass of a cubic decimeter of water to be 850 grams. What is the percent of error in this laboratory scale?

   

Research Links:

• Significant Figure Rules - Diamond Bar High School
• Significant Digits - Roanoke Valley Governor's School

Chemistry Class

#1. 50.594%

#2

1. 4
2. 3
3. 3
4. 2
5. 2
6. 4
7. 2
8. 3

% error answers:

1. 11%
2. 15%