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 1400 kg/h · 30% saltStream 2750 kg/h · 5% saltStream 3ṁ₃ = ? kg/h

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

ṁ1 = 400 kg/hx1 = 30 %ṁ2 = 750 kg/hx2 = 5 %
ṁ3 = kg/h
2.Easy
MixerStream 1850 kg/h · 10% NaOHStream 2950 kg/h · 15% NaOHStream 3x₃ = ? %

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

ṁ1 = 850 kg/hx1 = 10 %ṁ2 = 950 kg/hx2 = 15 %
x3 = %
3.Medium
MixerStream 1900 kg/h · 20% saltStream 2ṁ₂ = ? · 35% 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 = 20 %x2 = 35 %x3 = 25 %
ṁ2 = kg/h
4.Medium
MixerStream 1700 kg/h · 20% sugarStream 2ṁ₂ = ? · 50% sugarProduct40% sugar

How much of stream 2 must be added each hour to stream 1 so that the blended product contains 40% sugar? Find ṁ2.

ṁ1 = 700 kg/hx1 = 20 %x2 = 50 %x3 = 40 %
ṁ2 = kg/h
5.Hard
EvaporatorFeed F4200 kg/h · 5% NaOHProduct PP = ? · 45%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 = 4200 kg/hxF = 5 %xP = 45 %
P = kg/h
6.Hard
EvaporatorFeed F2000 kg/h · 12% saltProduct P30% saltVapour W (pure water)W = ? kg/h

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

F = 2000 kg/hxF = 12 %xP = 30 %
W = kg/h

Answer key

  1. 1. ṁ3 = 1150 kg/h
  2. 2. x3 = 12.64 %
  3. 3. ṁ2 = 450 kg/h
  4. 4. ṁ2 = 1400 kg/h
  5. 5. P = 466.7 kg/h
  6. 6. W = 1200 kg/h

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