SI Units - Online Tutor, Practice Problems & Exam Prep

SI Units vs. Derived Units

In this video, we'll take a look at the SI units. As we explore calculations in analytical chemistry, it'll be important to commit to memory some of our SI base units as well as our SI derived units. So if we take a look, it says that the international system of units provides 9 units of measurement that are going to be used when we're talking about SI units. Now, when it comes to the SI base units, we're going to have these 9 physical quantities being discussed. Of these 9, I would say the first 6 are the most important. So if we take a look, when it comes to mass, the symbol that we use or the units that we talk about are kilograms. For length, we're discussing meters. Time will be in seconds. Temperature will be in Kelvin. Amounts of any substance, no matter what it is, we use 1 mole to talk about that amount. When it comes to electrical currents or amps, we're discussing amperes. The symbol here would just be a. Remember, an ampere is just charge per time, which would be coulombs per second. The final 3, which deals with luminous intensity, plane angle as well as solid angle, they're other SI base units but they're less important than the first six. The other 6 we'll, we'll discover in some way or another whether we're doing some type of stoichiometric calculations or with electrical current when we're talking about electrochemistry. Now from these SI base units, we have our SI derived units. Now here when we're talking about frequency, remember it's connected to the electromagnetic spectrum. And when we talk about the electromagnetic spectrum, we talk about frequency, wavelength energy. Frequency uses hertz for its units. And here, from the SI base units, it's just seconds inverse, or, one over seconds. When we're talking about force, we're talking about newtons. Here, it doesn't have any SI derived units. Its SI base units would be meters times kilograms over seconds squared. Pressure, we're used to seeing atmospheres being discussed. But really, when it comes to our SI derived units, we're really talking about pascals. And here, remember there are our SI derived units, which are the newtons, which we talked about with force over meter squared, and then we have our SI base units. When we're talking about energy work or quantity of heat involved, we're talking about joules. This is typically done when we're talking about chemical thermodynamics, if we're talking about entropy, enthalpy, Gibbs free energy, or if we're talking about thermochemistry when we're discussing heat. Power, when we talk about electrochemistry, we'll talk about current, we'll talk about watts, we'll talk about things like that, resistance. Electrical charge, we discussed up above. Remember when we talked about amperes as being charge per time. Here when we're talking about charge, the unit is the coulomb. Potential is voltage. These last 4 all deal with electrochemistry. They have some physics involved with them. When we get to the electrochemistry chapter, we'll talk in greater detail about, these last 4 in particular. But just remember, we have our SI base units, and the SI base units are connected to our SI derived units as well. So keep in memory some of the most common ones that we will tend to see as we progress deeper and deeper into analytical chemistry.