Guys, in this video we're going to take a look at buoyancy within air. Now, in analytical chemistry we're trying to minimize as many factors as possible in order to ensure that we get the highest level of precision and accuracy within our measurements. Now, one of the factors that we have to take into effect is buoyancy. Buoyancy is the upward force exerted on an object in a liquid or gas. Here since we're looking at buoyancy in air, we're looking at how buoyancy works within a gas. Now, even something as simple as weighing an object on an analytical balance has some level of uncertainty associated with it. Remember there are two forces at work. There is the downward force upon the object as a result of gravity. We can use the variables *a* or *g* to represent it with a value of 9.8ms2. But here when we put an object on an analytical balance we have to take into account that there is airflow. This airflow will distort our true mass of the object. This airflow is buoyancy. It's the upward force upon the object. So even when you put it in a closed analytical balance there is some level of uncertainty associated with the mass that you're recording.

Here the equation below will allow us to calculate the true mass of the object as though it exists within a vacuum. If it exists within a vacuum, this eliminates airflow entirely. So we'll get the actual mass of the object. If we take a look here at this buoyancy equation we're going to say *m* here represents our true mass. This *m* here is our apparent mass, the mass that you read off of the analytical balance once you weighed your analyte. *D _{a}* represents the density of air which has a density of 0.0012gml when the pressure is 1 bar and the temperature is 25 degrees Celsius.

*D*represents the density of our calibration weights. And here if it's a standard calibration weight its density will be 8gml, but you have to pay very close attention to the question because different types of metals and alloys can be used in place of a standard calibration weight. They each would have their own different density. So if it was using something that was not a standard calibration weight, they would give you a new density to input into the formula. Finally,

_{w}*d*just represents the density of the weighed object. So remember, anytime you weigh anything there is a level of uncertainty associated with airflow. There's that upward force, that buoyancy force that'll distort our true mass. This equation allows us to weigh the mass as though it exists within a vacuum, which eliminates the whole idea of airflow.

Now that we've seen this equation we'll apply it to the example that we see below. So click on the next video and see how we approach that problem.