Category: Chemical Engineering Math
"Published in Newark, California, USA"
Calculate the molarity of a solution containing 10.0 grams of sulfuric acid in 500 mL of solution. (MW of H2SO4 is 98.1)
Solution:
The molarity of a solution is defined as the number of moles of a solute per liter of a solution.
In this problem, the weight of solute which is sulfuric acid and the volume of the solution are given.
The number of moles of sulfuric acid is
Therefore, the molarity of sulfuric acid solution is
Category: Chemical Engineering Math
"Published in Vacaville, California, USA"
Acetone is the chemical solvent present in the fingernail polish remover. Its percent composition is 62.0% carbon, 10.4% hydrogen, and 27.5% oxygen. What is the empirical formula for the compound?
Solution:
Basis: 100 grams of sample
Weight of each components:
Weight of carbon is
Weight of hydrogen is
Weight of oxygen is
Moles of each components:
Moles of carbon is
Moles of hydrogen is
Moles of oxygen is
From
the number of moles of each component, we need to divide all of them by
their least number of moles which is oxygen in order to get the number
of atoms in a sample.
Number of carbon in a sample is
Number of hydrogen in a sample is
Number of oxygen in a sample is
Therefore, the empirical formula for acetone is
Category: Chemical Engineering Math
"Published in Vacaville, California, USA"
Percent composition data for the chlorofluorocarbon Freon-12 by mass are: 9.933% carbon, 58.63% chlorine, and 31.44% fluorine. Based on these data, what is the empirical formula of Freon-12?
Solution:
Basis: 100 grams of sample
Weight of each components:
Weight of carbon is
Weight of chlorine is
Weight of fluorine is
Moles of each components:
Moles of carbon is
Moles of chlorine is
Moles of fluorine is
From the number of moles of each component, we need to divide all of them by their least number of moles which is carbon in order to get the number of atoms in a sample.
Number of carbon in a sample is
Number of chlorine in a sample is
Number of fluorine in a sample is
Therefore, the empirical formula for Freon-12 is
Category: Chemical Engineering Math
"Published in Newark, California, USA"
Two gases, HBr and CH4, have molecular weights 81 and 16, respectively. The HBr effuses through a certain small opening at the rate of 4 mL/sec. At what rate will the CH4 effuse through the same opening?
Solution:
Since the rate of flow of the gases as well as their molecular weight are involved in the problem, then we have to us the Graham's Law of Effusion and Diffusion. What is the difference between effusion and diffusion? Effusion is the process in which a gas escapes from one chamber of a vessel by passing through a very small opening or orifice while diffusion is mixing of molecules of different gases by random motion and collision until the mixture becomes homogeneous.
The rate of effusion or diffusion of a gas is inversely proportional to the square root of its density or molecular weight. The equation of Graham's Law of Effusion and Diffusion can be written as follows
or
From the given problem, therefore, the rate of effusion of CH4 through the small opening is
Category: Chemical Engineering Math
"Published in Newark, California, USA"
What pressure is required to compress 5 liters of gas at 1 atm pressure to 1 liter at a constant temperature?
Solution:
At the given problem, if the temperature is constant during the compression of a gas, then it is a principle of Boyle's Law. The volume of a gas is inversely proportional to its pressure. The equation for Boyle's Law can be written as follows
or
Therefore, the pressure of a gas after it is compressed to 1 liter is
