Material Balance Without Reaction Questions and Answers

Answer: C

The salt appears in only two streams, so its balance contains the fewest unknowns and often solves directly. Choosing the species with fewest appearances is the general tactic. The water balance then follows from the total.

Answer: D

Correct answer: 800 kilograms per hour

The salt is the tie component, since all of it leaves in the product: \[ 1000\times0.05 = 50\ \mathrm{kg/h\ salt}, \qquad \frac{50}{0.25} = 200\ \mathrm{kg/h\ product}, \] so the water evaporated is \( 1000-200 = 800 \) kg/h. Working from the salt rather than the water is what makes this a one-line calculation.

Answer: A

Correct answer: 2 - 4 - 1 - 3

Draw and label the flowsheet first, because the diagram defines the unknowns. Choose a basis next, since without one the problem has no scale and cannot be solved numerically. Count degrees of freedom then, to confirm it is determinate and to find where to start. Only then write and solve the balances. Working in this order turns most problems into arithmetic.

Answer: B

Its amount is the same on both sides, so the ratio of the two streams follows at once. Ash in a coal problem and nitrogen in a combustion problem are the standard examples. Inert species are the natural place to look for one.

Answer: C

Water is the species being transferred, so its amount changes between streams and it cannot tie them together. The other three all pass through in unchanged quantity. A tie component must not take part in the transfer.

Answer: D

Eighty kilograms of dry solid at ninety-five per cent gives a product of about eighty-four point two kilograms, so about fifteen point eight kilograms of water leaves. Subtracting the percentages directly gives fifteen and is wrong.

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the advantage. The bone dry solid passes through unchanged, so it serves as a tie component and every stream can be referred to it. Working on a wet basis means both the numerator and the denominator change as water leaves, which makes the algebra needlessly awkward - and it is why moisture content in drying is quoted as kilograms of water per kilogram of dry solid.

Answer: B

The carrier gas is inert and appears in only two streams, which makes it the natural tie component. The solute is the species of interest but its balance carries the most unknowns. Solving the easy balance first exposes the harder one.

Answer: C

A splitter divides a stream without altering what it contains, so its balances are far simpler. Recognising this class of unit early saves writing species balances that carry no information. Its outlets differ only in how much flows through each.

Answer: D

The first two are correct and are the basis of the familiar lever rule. The third is wrong for the flows themselves, since the material balances alone determine them; the energy balance is needed for the reboiler and condenser duties.