Stoichiometry Problem - Material Balance, 14

Category: Chemical Engineering Math, Algebra

"Published in Suisun City, California, USA"

In order to carry out nitration reaction, it is desired to have a mixed acid containing 39% HNO₃, 42% H₂SO₄, and 19% H₂O by weight. Nitric acid of 68.3% by weight is readily available. Calculate the

(a) required strength of sulfuric acid in order to obtain the above mixed acid and
(b) the weight ratio of nitric acid to sulfuric acid to be mixed.

Solution:

The given word problem is about the mixing of different acids which involves the principles of Stoichiometry. The concentration or strength of concentrated sulfuric acid is unknown and we need to solve it. The total amount of a substance in the reactants or incoming ingredients must be equal to the total amount of a substance in the final products. In short, the Law of Conservation of Mass must be followed all the time. Since all incoming substances are acids, then there's no chemical reactions involved in the mixture. To illustrate the given problem, it is better to draw the flow diagram as follows

Photo by Math Principles in Everyday Life

Since the amount of concentrated nitric acid, concentrated sulfuric acid, and mixed acids are not given in the problem, let's assign a basis of 100 kg of mixed acid in the problem.

Basis: 100 kg of Mixed Acids

Let x = be the amount of Concentrated Nitric Acid
      y = be the amount of Concentrated Sulfuric Acid

Overall Material Balance of Mixer:

Material Balance of Nitric Acid:

 

Substitute the value of x to the above equation, we have

Material Balance of Sulfuric Acid:

 

 

Therefore, the concentration or strength of Concentrated H₂SO₄ is

The weight ratio of Concentrated HNO₃ to Concentrated H₂SO₄ is

Stoichiometry Problem - Material Balance, 13

Category: Chemical Engineering Math, Algebra

"Published in Suisun City, California, USA"

A gas mixture containing 15% mole A and 85% mole inerts is fed to an absorption tower where it is contacted with liquid solvent B which absorbs A. The mole ratio of solvent to gas entering tower is 2:1. The gas leaving the absorber contains 2.5% mole A, 1.5% mole B, and the rest inerts. Find

(a) the percentage recovery of solute A, and
(b) the fraction of the solvent B fed to a column lost in gas leaving the tower.

Note that during the process, some solvent evaporates and gets added in the gas leaving the tower.

Solution:

The given word problem is about gas absorption of solute A with solvent B which involves the principles of Stoichiometry. The total amount of a substance in the reactants or incoming ingredients must be equal to the total amount of a substance in the final products. In short, the Law of Conservation of Mass must be followed all the time. To illustrate the given problem, it is better to draw the flow diagram as follows

Photo by Math Principles in Everyday Life

Basis: 100 kmole of Gas Entering in absorption tower

Let x = be the amount of Gas Leaving from absorption tower
      y = be the amount of Solute A - Solvent B leaving from absorption tower

If the mole ratio of solvent to gas entering is 2:1, then it follows that

Overall Material Balance of Absorption Tower:

Material Balance of Inerts:

Material Balance of Solute A:

Therefore, the percentage recovery of Solute A is

The amount of loss for Solvent B during the absorption is 

Therefore, the fraction of loss for Solvent B is

Stoichiometry Problem - Material Balance, 12

Category: Chemical Engineering Math, Algebra

"Published in Suisun City, California, USA"

Soya bean seeds are extracted with hexane in batch extractors. The flaked seeds are found to contain 18.6% oil, 69% solids, and 12.4% moisture by weight. At the end of the extraction process, cake (meal) is separated from hexane-oil mixture. The cake is analyzed to contain 0.8% oil, 87.7% solids, and 11.5% moisture by weight. Find the percentage recovery of oil. 

Solution:

The given word problem is about extraction of soya bean with hexane to collect soya bean oil which involves the principles of Stoichiometry. The total amount of a substance in the reactants or incoming ingredients must be equal to the total amount of a substance in the final products. In short, the Law of Conservation of Mass must be followed all the time. To illustrate the given problem, it is better to draw the flow diagram as follows

Photo by Math Principles in Everyday Life

Basis: 100 kg of Flaked Seeds

Let x = be the amount of Hexane
      y = be the amount of Cake
      z = be the amount of Hexane-Oil

Overall Material Balance of Batch Extractors:

Material Balance of Solids:

The amount of oil in cake is calculated as follows

If we know the amount of oil in flaked seeds and cake, then we can calculate the amount of oil recovered or extracted as follows

Therefore,