Q: A solution contains 4.0 M MgCl$$_2 at 20$^ ext{o}C $$with a density of 1.10 g/mL. Which formula would you use to calculate the weight percent of MgCl$$_2 in $$the solution?

$$\text{wt\%} = \frac{\text{mass}_{\text{solute}}}{\text{mass}_{\text{solution}}} \times 100$$

Q: Given 620 kg of dinitrogen pentoxide (N$$_2O$_5$$), how many moles of N$$_2O$_5$$ are present? (Molar mass of N$$_2O$_5 = 108 g/$$mol)

$$\frac{620,000\ \text{g}}{108\ \text{g/mol}} = 5,741\ \text{mol}$$

Q: A sample of seawater contains 0.129 wt% Mg$$^{2+}$$ and has a specific gravity of 1.03. What is the formula to convert this concentration to ppm?

$$\text{ppm} = \frac{\text{mass}_{\text{solute}}}{\text{mass}_{\text{solution}}} \times 10^6$

Q: Which formula would you use to calculate the percent excess reactant in a reaction?

$$\%\ \text{Excess} = \frac{\text{Supplied ER} - \text{Theoretical ER}}{\text{Theoretical ER}} \times 100$$

Q: What is the degree of completion if 80 g of limiting reactant is supplied and 60 g is converted to product?

$$\frac{60}{80} \times 100 = 75\%$$

Q: Which formula is used to calculate molarity (M)?

$$M = \frac{n_{\text{solute}}}{V_{\text{soln}}}$$

Question 1

Which of the following best describes the main purpose of chemical engineering calculations?

Accepted Answer

To interpret quantitative data and apply the laws of conservation of mass and energy

Question 2

A solution contains 4.0 M MgCl$$_2 at 20$^	ext{o}C $$with a density of 1.10 g/mL. Which formula would you use to calculate the weight percent of MgCl$$_2 in $$the solution?

Accepted Answer

$$	ext{wt\%} = \frac{	ext{mass}_{	ext{solute}}}{	ext{mass}_{	ext{solution}}} 	imes 100$$

Question 3

Which of the following is the correct definition of a mole?

Accepted Answer

The amount of substance containing Avogadro's number of particles

Question 4

Given 620 kg of dinitrogen pentoxide (N$$_2O$_5$$), how many moles of N$$_2O$_5$$ are present? (Molar mass of N$$_2O$_5 = 108 g/$$mol)

Accepted Answer

$$\frac{620,000\ 	ext{g}}{108\ 	ext{g/mol}} = 5,741\ 	ext{mol}$$

Question 5

Which equation correctly expresses the relationship for density ($$\rho$$)?

Accepted Answer

$$\rho = \frac{m}{V}$$

Question 6

A sample of seawater contains 0.129 wt% Mg$$^{2+}$$ and has a specific gravity of 1.03. What is the formula to convert this concentration to ppm?

Accepted Answer

$$	ext{ppm} = \frac{	ext{mass}_{	ext{solute}}}{	ext{mass}_{	ext{solution}}} 	imes 10^6$

Question 7

Which of the following best describes the limiting reactant in a chemical reaction?

Accepted Answer

The reactant that is completely consumed first

Question 8

An oil has a specific gravity of 0.81. What is its API gravity? (Use $$	ext{API} = \frac{141.5}{	ext{S.G.}} - 131.5)$$

Accepted Answer

$$\frac{141.5}{0.81} - 131.5 = 43.98$$

Question 9

Which formula would you use to calculate the percent excess reactant in a reaction?

Accepted Answer

$$\%\ 	ext{Excess} = \frac{	ext{Supplied ER} - 	ext{Theoretical ER}}{	ext{Theoretical ER}} 	imes 100$$

Question 10

In the reaction $$C_6H_{14} + O_2$ \rightarrow H_2O + CO_2$, 120 g of butane is burned with 600 g of O_2$. If the reaction goes to 90% completion, which is the limiting reactant? (Molar mass: C_6H$$_{14}$$ = 86 g/mol, O_2$ = 32 g/mol)

Accepted Answer

Butane ($$C_6H_{14})$$

Question 11

Which of the following is NOT a process variable in chemical engineering calculations?

Accepted Answer

Color

Question 12

What is the degree of completion if 80 g of limiting reactant is supplied and 60 g is converted to product?

Accepted Answer

$$\frac{60}{80} 	imes 100 = 75\%$$

Question 13

Which formula is used to calculate molarity (M)?

Accepted Answer

$$M = \frac{n_{	ext{solute}}}{V_{	ext{soln}}}$$

Question 14

A mixture contains 60% malachite (Cu$$_2CO$_3(OH$$)$$_2) $$and 40% emerald green (Cu(C$$_2H$_3O$_2$$)$$_2$$·3CuAs$$_2O$_4). $$What is the first step to calculate the mass of copper that can be obtained from 1 tonne of this mixture?

Accepted Answer

Calculate the mass of each component in the mixture

Question 15

Which of the following is the correct formula for specific gravity (S.G.)?

Accepted Answer

$$S.G. = \frac{ho_{	ext{substance}}}{ho_{	ext{water}}}$$

Question 16

Which of the following best describes the Law of Conservation of Mass?

Accepted Answer

The total mass of reactants equals the total mass of products in a chemical reaction

Chemical Engineering Calculations: Foundational Concepts and Applications

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