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# Physical Science for Armed Services Vocational Aptitude Battery (ASVAB) Study Guide (page 3)

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### Concentration, Acids, Bases, and pH

Concentration is a measure of how much solute is in a solution. A solute is a substance that is dissolved in a medium, and a solvent is a medium in which a solute is dissolved. For instance: salt water is a solution—a homogenous mixture consisting of the solute (salt) and the solvent (water).

Acids are proton donors; they release hydrogen ions (protons). Acids have a sour taste. Bases are proton acceptors; they take up hydrogen ions. Bases have a bitter taste and feel slippery. Strong bases take up more hydrogen ions than weak bases.

The relative concentration of hydrogen ions is measured in concentration units called pH units. The pH scale runs from 0 to 14. A substance with a pH of 7 is neutral. Substances such as vinegar and orange juice, with a pH of less than 7, are considered acidic. Substances such as soaps and ammonia, with a pH of more than 7, are considered alkaline.

### Measurement

Although you may be more familiar with the English system of measurement (inches, pounds, and so on), the metric system is the standard system of measurement in science. The metric system is a decimal system based on multiples and fractions of ten. The meter (m) is the standard unit of length in the decimal system:

1 meter = 100 centimeters (cm)
1 kilometer (km) = 1,000 meters

The gram (g) is the metric system unit of mass:

1 gram = 1,000 milligrams (mg)
1 kilogram (kg) = 1,000 grams

Volume, the amount of space occupied by a fluid or body, is usually measured using the liter. The cubic meter (cm3) is actually the standard metric unit of volume, but it is infrequently used.

1 liter (L) = 1,000 milliliters (ml)
1 cm3 = 1 ml

In science, temperature is most often measured using degrees Celsius (°C). On the Celsius scale, the freezing point for water is 0° and the boiling point for water is 100°. This makes it much easier to use than the Fahrenheit scale, which has a freezing point of 32° and a boiling point of 212°. The two equations below show how to convert a temperature measurement from one scale to the other.

Other important equations are as follows:

• Speed is the distance covered or traveled by an object per a certain unit or amount of time:
• Speed = distance/time

• Momentum is the tendency of an object to continue moving in the same direction: Momentum = mass × speed
• Work is a force applied to an object which, in turn, results in movement:
• Work = force × distance

• Power is the rate at which work is done. It is measured in joules (J):
• Power = work/time

Note: Mass should not be confused with weight. Mass is the measurement of the amount of matter in an object. Weight is the force by which gravity attracts a body to Earth.

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