1.3.1 The Measurement of Matter

Question 1

The Measurement of Matter

Answer 1

• A measurement is meaningless unless it has units associated with it.
• The Systèm International d’Unités (SI) was developed as a convenient and uniform system of measurement.
• Some SI units are based on amounts that are too large or small to be useful for chemists, so units derived from SI units are commonly used.

Question 2

SI units

Answer 2

• A measurement is meaningless unless is has units associated with it. For example, describing the length of a football field as “100” is insufficient. The length should be given as “100 yards”.
• The Systèm International d’Unités (SI) was developed as a convenient and uniform system of measurement.
• All SI units are built upon seven base SI units. These units are the meter (length), the kilogram (mass), the kelvin (temperature), the mole (chemical amount), the ampere (electric current), and the candela (luminous intensity).

Question 3

derived units

Answer 3

• units obtained by combining two or more of the base SI units. For example, the joule is a unit of energy that combines kilograms, meters, and seconds.
• Derived units include the joule (energy), the newton(force), the watt (power), the pascal (pressure), the coulomb (electric charge), and the volt (electric potential difference)

Question 4

prefixes

Answer 4

• Greek prefixes are used to modify SI units. For example, one kilometer (km) is equal to 103 meters (one thousand meters).
• Greek prefixes can be used with any base SI unit. For
  example, if a very small chemical amount is being measured, it might be given in picomoles (pmol), or 10–12 moles (one trillionth of a mole).
• Although the base SI unit of mass is the kilogram, Greek prefixes are used to modify grams. For example, one milligram (mg) is equal to 10–3 grams (one thousandth of a gram), or one millionth of a kilogram.

Question 5

note

Answer 5

• Some SI units are based on amounts that are too large or small to be useful for chemists, so units derived from SI units are commonly used.
• The unit commonly used by chemists for volume is the liter (L), which is equal to 10–3 m 3.
• The unit commonly used for mass is the gram (g), which is equal to 10–3 kilograms.
• A unit commonly used in the lab for temperature is the degree Celsius (˚C). To convert from temperature in kelvins to temperature in degrees Celsius, subtract 273.15. However, many calculations in chemistry require that the temperature be in kelvins.
• A unit commonly used for pressure is the atmosphere (atm), which is equal to 101,325 pascals. The atmospheric pressure at sea level is approximately one atmosphere, making this unit very convenient.

Question 6

There are seven base SI units that were established as the international norm for all scientific endeavors. Since then, many derived units have been established. These are units that are combinations of the seven basic units. Which of the following choices is not a base SI unit?

Answer 6

• liter

Question 7

One kilogram is equal to about 2.20 pounds. Both kilograms and pounds are units of mass. What is the equivalent weight in pounds of a 37.5 kilogram object?

Answer 7

• 82.5 lb

Question 8

A student makes measurements of a line. The student records the lengths as 20.5, 20.4, and 20.2. Which statement best describes this data?

Answer 8

• It is impossible to say.

Question 9

Suppose that you were practicing for a track event at a track outside of your hometown. This track is 1/4 mile long, while your home track is 1/2 mile long. You time your workout and find that you ran a total of 4 laps in 2 minutes and 48 seconds. You then tell your coach that you ran 4 laps in 2 minutes and 48 seconds. From a scientific point of view, what is wrong with the information you gave your coach?

Answer 9

• Your coach needs to know more information about the unit of length for 1 lap. A lap could be 1/4 mile, 1/2 mile, or any other length.

Question 10

Which of the following statements about measurements is true?

Answer 10

• Numerical measurements must always have units written after them.

Question 11

The lecturer stated that “the bottom line in making or reporting scientific (or any) measurements is…” Which of the following best completes this statement?

Answer 11

• associating units with measurements.

Question 12

Which of the following terms would represent one-thousandth of a liter?

Answer 12

• milliliter

Question 13

Which of the following is not a base SI unit?

Answer 13

• inch

Question 14

Which of the following units is used to measure a different quantity than the other units?

Answer 14

• second

Question 15

A cubit is equal to “the distance from your elbow to your fingertips.” Which statement best describes what is inherently wrong with this definition of a cubit as a unit of length?

Answer 15

• The distance from one’s elbow to one’s fingertips is different for every person, so the unit is not exact.