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 · 10% NaOHStream 2300 kg/h · 15% NaOHStream 3x₃ = ? %

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

ṁ1 = 100 kg/hx1 = 10 %ṁ2 = 300 kg/hx2 = 15 %
x3 = %
2.Easy
MixerStream 1900 kg/h · 30% saltStream 21000 kg/h · 15% saltStream 3ṁ₃ = ? kg/h

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

ṁ1 = 900 kg/hx1 = 30 %ṁ2 = 1000 kg/hx2 = 15 %
ṁ3 = kg/h
3.Medium
MixerStream 1550 kg/h · 50% NaOHStream 2ṁ₂ = ? · 15% NaOHProduct45% NaOH

How much of stream 2 must be added each hour to stream 1 so that the blended product contains 45% NaOH? Find ṁ2.

ṁ1 = 550 kg/hx1 = 50 %x2 = 15 %x3 = 45 %
ṁ2 = kg/h
4.Medium
MixerStream 1900 kg/h · 30% saltStream 2ṁ₂ = ? · 20% saltProduct25% salt

How much of stream 2 must be added each hour to stream 1 so that the blended product contains 25% salt? Find ṁ2.

ṁ1 = 900 kg/hx1 = 30 %x2 = 20 %x3 = 25 %
ṁ2 = kg/h
5.Hard
EvaporatorFeed F3900 kg/h · 18% saltProduct PP = ? · 35%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 = 3900 kg/hxF = 18 %xP = 35 %
P = kg/h
6.Hard
EvaporatorFeed F3800 kg/h · 11% sugarProduct P65% 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 = 3800 kg/hxF = 11 %xP = 65 %
W = kg/h

Answer key

  1. 1. x3 = 13.75 %
  2. 2. ṁ3 = 1900 kg/h
  3. 3. ṁ2 = 91.67 kg/h
  4. 4. ṁ2 = 900 kg/h
  5. 5. P = 2006 kg/h
  6. 6. W = 3157 kg/h

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