Test Yourself - Process Analysis Fundamentals

Recall that we use Molar Mass, aka molecular weight, to convert between mass and molar units.

The molar mass of ethanol (EtOH) is 46.068 g/mol.

Convert 100 g of EtOH into moles of EtOH.

• 2.17 mol

• 0.46 mol

• 46 mol

Answer explanation

Divide the weight in grams by the molar mass to achieve the desired units (mol).

Recall “wt%” stands for weight percent.

It signifies a percentage mass.

What is 0.5 wt% of 100 kg?

• 0.5 kg

• 5 kg

• 50 kg

Answer explanation

0.5wt% is a small percentage.

For comparison, 50wt% is HALF the total mass.

Unit conversion is readily applied in process engineering problems.

A mass flowrate of n-hexane is 200 g/min.

What is the above flowrate in kg/hr?

• 333 kg/hr

• 0.2 kg/hr

• 12 kg/hr

Answer explanation

Both the mass and time unit require conversion to achieve the desired units.

Recall that mass fraction describes the ratio of a substances’ mass to the total mass.

You have 20 kg of substance A, and combine it with 80kg of substance B.

What is the mass fraction of substance A in the mixture?

• 0.2 kg A / kg total

• 0.25 kg A / kg total

• 0.4 kg A / kg total

Answer explanation

The total mass of the mixture is 100g.

To obtain the mass fraction of substance A, divide its mass (20kg) by the total mass (100kg).

Recall “mol%” stands for molar percent. It signifies percentage moles.

What is 12 mol% of 100 mols?

• 1.2 mols

• 12 mol

• 120 mol

Answer explanation

I.e., "12% of 100"

Recall we utilise specific gravity (SG) to describe substances’ relative density to water.

 

Kerosene has a specific gravity (S.G) of 0.82.

What is kerosene's density?

• 8200 kg/m3

• 82 kg/m3

• 820 kg/m3

Answer explanation

To convert specific gravity (SG) to density in kilograms per cubic meter (kg/m3), multiply the specific gravity by 1,000.

This is because the specific gravity of water is taken as 1,000 kg/m³.

Recall "molar concentration" (mol/L) of ions in solution can be abbreviated simply as M, pronounced "molar".

51 g of Ca(NO₃)₂, having a molar mass of 204.17 g/mol, is completely dissolved into 1 L of water.

What is the molarity of the resulting solution?

• 1 M

• 4 M

• 0.25 M

Answer explanation

Employ unit conversion to convert solute mass to moles and divide this result by the solution volume.

Recall 1 mol/L is equivalent to a 1 molar solution (1 M).

According to the conservation of mass law, mass is neither created nor destroyed.

For the splitter unit shown, what value must A be?

• 17 kg/s

• 20 kg/s

• 23 kg/s

Answer explanation

The sum of mass entering the splitter must equal the sum of mass leaving it.

Process analysis diagrams should be annotated with known system values.

For the splitter unit shown, what value must A be?

• 1.2 wt% NaCl

• 2 wt% NaCl

• 3.3 wt% NaCl

Answer explanation

This unit is a splitter.

Therefore, the fraction of NaCl in each stream remains unchanged.

All streams share the same composition.