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 1100 kg/h · 30% saltStream 2750 kg/h · 20% saltStream 3x₃ = ? %

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

ṁ1 = 100 kg/hx1 = 30 %ṁ2 = 750 kg/hx2 = 20 %
x3 = %
2.Easy
MixerStream 1150 kg/h · 5% sugarStream 2450 kg/h · 15% sugarStream 3ṁ₃ = ? kg/h

Two sugar solutions are mixed at steady state. Find the outlet flow rate ṁ3.

ṁ1 = 150 kg/hx1 = 5 %ṁ2 = 450 kg/hx2 = 15 %
ṁ3 = kg/h
3.Medium
MixerStream 1850 kg/h · 10% saltStream 2ṁ₂ = ? · 50% saltProduct20% salt

How much of stream 2 must be added each hour to stream 1 so that the blended product contains 20% salt? Find ṁ2.

ṁ1 = 850 kg/hx1 = 10 %x2 = 50 %x3 = 20 %
ṁ2 = kg/h
4.Medium
MixerStream 1550 kg/h · 40% NaOHStream 2ṁ₂ = ? · 20% NaOHProduct35% NaOH

How much of stream 2 must be added each hour to stream 1 so that the blended product contains 35% NaOH? Find ṁ2.

ṁ1 = 550 kg/hx1 = 40 %x2 = 20 %x3 = 35 %
ṁ2 = kg/h
5.Hard
EvaporatorFeed F2700 kg/h · 5% NaOHProduct PP = ? · 65%Vapour W (pure water)0% NaOH

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

F = 2700 kg/hxF = 5 %xP = 65 %
P = kg/h
6.Hard
EvaporatorFeed F3300 kg/h · 17% sugarProduct P55% sugarVapour W (pure water)W = ? kg/h

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

F = 3300 kg/hxF = 17 %xP = 55 %
W = kg/h

Answer key

  1. 1. x3 = 21.18 %
  2. 2. ṁ3 = 600 kg/h
  3. 3. ṁ2 = 283.3 kg/h
  4. 4. ṁ2 = 183.3 kg/h
  5. 5. P = 207.7 kg/h
  6. 6. W = 2280 kg/h

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