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 1950 kg/h · 20% saltStream 2550 kg/h · 25% saltStream 3x₃ = ? %

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

ṁ1 = 950 kg/hx1 = 20 %ṁ2 = 550 kg/hx2 = 25 %
x3 = %
2.Easy
MixerStream 1450 kg/h · 35% NaOHStream 2150 kg/h · 25% NaOHStream 3x₃ = ? %

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

ṁ1 = 450 kg/hx1 = 35 %ṁ2 = 150 kg/hx2 = 25 %
x3 = %
3.Medium
MixerStream 1300 kg/h · 10% saltStream 2ṁ₂ = ? · 40% saltProduct30% salt

How much of stream 2 must be added each hour to stream 1 so that the blended product contains 30% salt? Find ṁ2.

ṁ1 = 300 kg/hx1 = 10 %x2 = 40 %x3 = 30 %
ṁ2 = kg/h
4.Medium
MixerStream 1450 kg/h · 50% NaOHStream 2ṁ₂ = ? · 10% 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 = 450 kg/hx1 = 50 %x2 = 10 %x3 = 35 %
ṁ2 = kg/h
5.Hard
EvaporatorFeed F2000 kg/h · 11% NaOHProduct P60% 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 = 2000 kg/hxF = 11 %xP = 60 %
W = kg/h
6.Hard
EvaporatorFeed F1200 kg/h · 12% sugarProduct P35% 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 = 1200 kg/hxF = 12 %xP = 35 %
W = kg/h

Answer key

  1. 1. x3 = 21.83 %
  2. 2. x3 = 32.5 %
  3. 3. ṁ2 = 600 kg/h
  4. 4. ṁ2 = 270 kg/h
  5. 5. W = 1633 kg/h
  6. 6. W = 788.6 kg/h

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