SI Units (Simplified): Study with Video Lessons, Practice Problems & Examples

The International System of Units (SI) comprises six base units essential for scientific measurements. These include the kilogram (kg) for mass, meter (m) for length, second (s) for time, kelvin (K) for temperature, mole (mol) for the amount of substance, and cubic meter (m³) for volume, though liters (L) are more commonly used. Understanding these units is crucial for accurate calculations in chemistry and physics, facilitating effective communication of scientific data and enhancing comprehension of concepts like molarity and density.

SI Units (Simplified) Concept 1

We're going to say here that the international system of units, SI, is related to the metric system, and it comes with 6 base units. Now, when it comes to these 6 base units, let's take a look. We have our physical quantity, and each of these physical quantities is attached to an SI base unit. This SI base unit name has a symbol. So, when it comes to mass, the SI base name is kilogram, and its symbol is kg. Okay? So, the SI base unit for mass is kilograms. Next, we have length. Length would be meters, which is abbreviated as m. Time would be seconds, which is abbreviated as just s. Temperature. The SI unit for temperature is kelvin, which is abbreviated as K, capital K. The amount of a substance, so you need to familiarize yourself with this particular term in terms of chemistry. The amount of the substance is the mole and its symbol is mol. So we just remove the e. Now, when you're doing calculations with moles later on in chemistry, you'll see them use either the full name or the symbol name. Okay? So just remember they're the same thing. Now for volume here, you'll see that there are 2 spots. That's because the top one is the SI base unit that we use, but you'll find time and time again that you'll not see the SI base unit used for volume, instead, you'll see the metric one. So the SI base unit for volume is going to be cubic meters, which is m3. And here, the metric of that is liters. You'll see liters more often than you will see cubic meters. And the symbol for liters is just a capital L. So here we have our 6 base units, as well as 1 metric unit. In terms of volume, the metric unit of liters is oftentimes used more than the SI unit of cubic meters.

SI Units (Simplified) Example 1

Which of the following values is given with SI units? So here we have 1.25 × 104 minutes, 6.82 × 10-3 milligrams, 25.6 °C, and 101.3 seconds. Alright. So, minutes is a unit of time. We know the SI unit for time is seconds, not minutes. Next, milligrams is our units for mass, but we know kilograms is the SI unit for mass. Celsius, units for temperature, but we know temperature should be in Kelvin when we're dealing with SI units. Here, out of all our options, option d is the correct choice. Seconds is an SI base unit.

Which of the following represents volume in SI units? 

• A. 2.71×10^–1 cm³
• B. 207.2 km²
• C. 5.81×10⁵ m³
• D. 582.28 mm

Convert 12 minutes into acceptable SI units.

• A. 720 s
• B. 0.20 s
• C. 3.33×10^–3 s
• D. 4.32×10⁴ s

Here’s what students ask on this topic:

What are the six base units of the International System of Units (SI)?

The six base units of the International System of Units (SI) are essential for scientific measurements. They include:

• Kilogram (kg) for mass
• Meter (m) for length
• Second (s) for time
• Kelvin (K) for temperature
• Mole (mol) for the amount of substance
• Cubic meter (m³) for volume, though liters (L) are more commonly used

Understanding these units is crucial for accurate calculations in chemistry and physics, facilitating effective communication of scientific data and enhancing comprehension of concepts like molarity and density.

Why is the liter (L) more commonly used than the cubic meter (m³) for volume in chemistry?

In chemistry, the liter (L) is more commonly used than the cubic meter (m³) for volume because it is more practical for the scale of measurements typically encountered. One cubic meter is equivalent to 1,000 liters, making it a very large unit for most laboratory settings. Liters are more convenient for measuring volumes of liquids and solutions, which are often in the range of milliliters (mL) to liters (L). This practicality makes liters a preferred unit in both educational and professional chemistry environments.

What is the SI unit for temperature and its symbol?

The SI unit for temperature is the kelvin, abbreviated as K. Unlike other temperature scales such as Celsius or Fahrenheit, the kelvin scale starts at absolute zero, the theoretical point where all molecular motion ceases. This makes it particularly useful in scientific contexts, as it provides a direct measure of thermal energy. The kelvin is crucial for calculations involving thermodynamics, physical chemistry, and other fields where precise temperature measurements are necessary.

How is the mole (mol) used in chemistry?

The mole (mol) is a fundamental unit in chemistry used to quantify the amount of a substance. One mole is defined as exactly 6.02214076 × 10²³ entities (Avogadro's number), which can be atoms, molecules, ions, or other particles. This unit allows chemists to relate macroscopic measurements to the number of particles involved in chemical reactions. For example, in stoichiometry, moles are used to balance chemical equations and calculate the amounts of reactants and products. Understanding the mole concept is essential for mastering topics like molarity, gas laws, and reaction yields.

What is the SI unit for mass and its symbol?

The SI unit for mass is the kilogram, abbreviated as kg. The kilogram is the only SI base unit with a prefix (kilo-) as part of its name. It is defined by the Planck constant, which is a fundamental constant of nature. The kilogram is crucial for various scientific and engineering applications, including chemistry, where it is used to measure the mass of substances. Accurate mass measurements are essential for preparing solutions, conducting experiments, and analyzing results.