Commonly Used Chemistry Metric Units – MCAT General Chemistry | MedSchoolCoach

Commonly Used Chemistry Metric Units

MCAT General Chemistry Chapter 1 - Section 1.2 - Stoichiometry

Sample MCAT Question - Commonly Used Chemistry Metric Units

All of the following pressures are equivalent EXCEPT:

a) 1 atm

b) 1.015 kPa

c) 760 torr

d) 760 mmHg

B is correct. 1.015 kPa.

1 atm of pressure is equivalent to 760 mmHg, 760 torr, or 1.015 Pa. The unit kPa is equal to 1,000 Pa. Consequently, 1 atm is equivalent to 1.012 kPa. 1.015 kPa is equivalent to 1,000 atm, 760,000 mmHg, or 760,000 torr.

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Commonly Used Chemistry Metric Units

Let’s discuss the metric units that are commonly used in MCAT general chemistry:

  • Concentration, or the relative abundance of one solute in a solvent, will be measured with molarity (M), and is defined as the number of moles of a given solute per one liter of solvent.

  • Volume is typically measured in liters, a non-SI unit, but you should be familiar with the conversion factor between liters and the meter cubed (m3), the SI unit of volume, which is given by the ratio of 1,000 liters per meter cubed. Note that this also means that one milliliter (mL) is equivalent to one centimeter cubed (cm3).

  • The SI unit of pressure is the Pascal (Pa), which is defined as a Newton per meter squared. We will also commonly encounter non-SI units of pressure, particularly Torr and millimeters of mercury (mmHg), both of which are approximately equal to 133 Pa, and the atmosphere (atm, equivalent to 105 Pa or 760 Torr or mmHg).

  • For temperature, we most commonly use the SI base unit Kelvin. You should also be familiar with how to convert between Kelvin and the commonly used Celsius, which is equal to the equivalent temperature in Kelvin minus 273. In equation form, this is would be: T(K) = T(°C) + 273. The Fahrenheit scale is not be used on the MCAT, and you do not need to memorize the conversion factor between Fahrenheit and Celsius.
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