Mass balance worksheet with answers

Free printable Mass balance worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy
MixerStream 1200 kg/h · 35% saltStream 2300 kg/h · 20% saltStream 3x₃ = ? %

Two salt solutions are mixed at steady state. Find the mass fraction of salt in the outlet x3.

ṁ1 = 200 kg/hx1 = 35 %ṁ2 = 300 kg/hx2 = 20 %
x3 = %
2.Easy
MixerStream 1550 kg/h · 35% NaOHStream 2150 kg/h · 15% NaOHStream 3x₃ = ? %

Two NaOH solutions are mixed at steady state. Find the mass fraction of NaOH in the outlet x3.

ṁ1 = 550 kg/hx1 = 35 %ṁ2 = 150 kg/hx2 = 15 %
x3 = %
3.Medium
MixerStream 1650 kg/h · 30% NaOHStream 2ṁ₂ = ? · 5% NaOHProduct15% NaOH

How much of stream 2 must be added each hour to stream 1 so that the blended product contains 15% NaOH? Find ṁ2.

ṁ1 = 650 kg/hx1 = 30 %x2 = 5 %x3 = 15 %
ṁ2 = kg/h
4.Medium
MixerStream 1700 kg/h · 5% sugarStream 2ṁ₂ = ? · 30% sugarProduct10% sugar

How much of stream 2 must be added each hour to stream 1 so that the blended product contains 10% sugar? Find ṁ2.

ṁ1 = 700 kg/hx1 = 5 %x2 = 30 %x3 = 10 %
ṁ2 = kg/h
5.Hard
EvaporatorFeed F2900 kg/h · 5% saltProduct PP = ? · 65%Vapour W (pure water)0% salt

An evaporator concentrates a salt solution by boiling off pure water. Find the product flow P in kg/h.

F = 2900 kg/hxF = 5 %xP = 65 %
P = kg/h
6.Hard
EvaporatorFeed F4100 kg/h · 7% NaOHProduct P30% NaOHVapour W (pure water)W = ? kg/h

An evaporator concentrates a NaOH solution by boiling off pure water. Find the water evaporated W in kg/h.

F = 4100 kg/hxF = 7 %xP = 30 %
W = kg/h

Answer key

  1. 1. x3 = 26 %
  2. 2. x3 = 30.71 %
  3. 3. ṁ2 = 975 kg/h
  4. 4. ṁ2 = 175 kg/h
  5. 5. P = 223.1 kg/h
  6. 6. W = 3143 kg/h

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