Category: Chemical Engineering Math
"Published in Vacaville, California, USA"
Analysis of a sample of ibuprofen, the active ingredient of Advil, shows that the sample contains 7.568 g of carbon, 0.881 g of hydrogen, and 1.551 g of oxygen. Use these data to calculate the empirical formula of ibuprofen.
Solution:
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
Since the number of atoms for carbon is a fraction which is 6.5, then we need to multiply all the atoms by 2 so that the number of atoms for empirical formula are all whole numbers. Therefore, the empirical formula for ibuprofen is
Category: Chemical Engineering Math
"Published in Newark, California, USA"
Calculate the pH for
(a) 0.02 M HCl
(b) 0.10 M HCN
Solution:
pH means "power of hydrogen". Some chemists say that pH means "potential of hydrogen". It is a measurement of acidity or alkalinity of a solution and it has a scale from 0 to 14. If pH is ranging from 0 to 6, then the solution is acidic. If pH is 7, then the solution is neutral like water, for example. If pH is ranging from 8 to 14, then the solution is alkaline. The pH of any acidic solution can be calculated by using the equation,
where [H+] is the concentration of hydrogen ion in molarity.
(a) For 0.02 M HCl solution
Since HCl is a strong acid, then it is completely ionized into hydrogen ion and chloride ion as follows
In a liter of solution, 0.02 moles of HCl is ionized completely into 0.02 moles of H+ and 0.02 moles of Cl-. Hence, the concentration of [H+] is 0.02.
Therefore, the pH of 0.02 M HCl solution is
If the pH of an acid is closer to 0, then it is a strong acid.
(b) For 0.10 M HCN solution
Since HCN is a weak acid, then it is partially ionized into hydrogen ion and cyanide ion as follows
In a liter of solution at equilibrium,
where x is moles of HCN that partially ionized. The ionization constant for HCN is given by the equation
From Table of Ionization Constants of Acids and Bases, Ka = 4.0 x 10-10 for hydrocyanic acid. The amount of HCN that partially ionized is
Since the value of Ka is less than 1 x 10-3, then we can neglect x at the denominator as follows
Hence, the concentration of hydrogen ion is
Therefore, the pH of 0.10 M HCN solution is
If the pH of an acid is closer to 7, then it is a weak acid.
Category: Chemical Engineering Math
"Published in Newark, California, USA"
A 50.0 g sample of calcium carbonate is reacted with 35.0 g of phosphoric acid. Calculate
(a) the number of grams of calcium phosphate that could be produced.
(b) the number of grams of excess reagent that will remain.
(Atomic Weights: Ca = 40, C = 12, O = 16, H = 1, and P = 31)
Solution:
The first thing that we need to do is to write the chemical equation of the reaction as follows
Balance the equation by putting the corresponding coefficients as follows
Molecular Weight of CaCO3:
Molecular Weight of H3PO4:
Molecular Weight of Ca3(PO4)2:
Molecular Weight of H2CO3:
Since the weight of the two reactants are given in the problem, then we need to find out which of them is limiting reagent. Limiting reagent is a substance that gives the least amount of product in the reaction. On the other hand, excess reagent is a substance that gives the excess amount of a substance in the reaction.
Weight of Ca3(PO4)2 from CaCO3:
Weight of Ca3(PO4)2 from H3PO4:
By comparing the weights of Ca3(PO4)2, CaCO3 will give us the least amount of product.
(a) Therefore, the limiting reagent is CaCO3 and the amount of Ca3(PO4)2 produced is
Since CaCO3 is the limiting reagent, then the amount of H3PO4 can be used in the reaction is
(b) Therefore, the excess amount of H3PO4 after the reaction is
