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 1350 kg/h · 10% NaOHStream 21000 kg/h · 35% NaOHStream 3x₃ = ? %

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

ṁ1 = 350 kg/hx1 = 10 %ṁ2 = 1000 kg/hx2 = 35 %
x3 = %
2.Easy
MixerStream 1950 kg/h · 25% saltStream 21000 kg/h · 15% saltStream 3ṁ₃ = ? kg/h

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

ṁ1 = 950 kg/hx1 = 25 %ṁ2 = 1000 kg/hx2 = 15 %
ṁ3 = kg/h
3.Medium
MixerStream 1250 kg/h · 5% sugarStream 2ṁ₂ = ? · 50% sugarProduct45% sugar

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

ṁ1 = 250 kg/hx1 = 5 %x2 = 50 %x3 = 45 %
ṁ2 = kg/h
4.Medium
MixerStream 1950 kg/h · 40% NaOHStream 2ṁ₂ = ? · 20% NaOHProduct25% NaOH

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

ṁ1 = 950 kg/hx1 = 40 %x2 = 20 %x3 = 25 %
ṁ2 = kg/h
5.Hard
EvaporatorFeed F4600 kg/h · 12% 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 = 4600 kg/hxF = 12 %xP = 45 %
P = kg/h
6.Hard
EvaporatorFeed F1700 kg/h · 18% saltProduct P65% 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 = 1700 kg/hxF = 18 %xP = 65 %
W = kg/h

Answer key

  1. 1. x3 = 28.52 %
  2. 2. ṁ3 = 1950 kg/h
  3. 3. ṁ2 = 2000 kg/h
  4. 4. ṁ2 = 2850 kg/h
  5. 5. P = 1227 kg/h
  6. 6. W = 1229 kg/h

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