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Question 1 of 7

How many moles are there in a solution if the solution contains 214 grams of Sucrose (RMM 342.3) at a mole fraction of 0.0250? Answer to 1 decimal place.

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moles
There are 25.0 moles altogether.

Moles of Sucrose = Mass/RMM = 214 / 342.3 = 0.62518 moles

Total Number of Moles = Number of Moles of A
Mole Fraction of A
Total Number of Moles = 0.62518
0.02500
Total Number of Moles = 25.00 = 25.0 to 1 dec pl

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Question 2 of 7

A powder contains 17.55 grams of Sodium Chloride, 7.46 grams of Potassium Chloride and 9.53 grams of Magnesium Chloride. What is the mole fraction of Potassium Chloride in the powder?

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The mole fraction of Potassium Chloride is 0.2.
RMM NaCl = 58.5      RMM KCl = 74.6      RMM MgCl2 = 95.3

Moles of NaCl = Mass / RMM = 17.55 / 58.5 = 0.3 moles
Moles of KCl = Mass / RMM = 7.46 / 74.6 = 0.1 moles
Moles of MgCl2 = Mass / RMM = 9.53 / 95.3 = 0.1 moles
Mole Fraction of A =                Number of Moles of A              
Total Number of Moles of All Components
Mole Fraction of KCl =          0.1          
0.3 + 0.1 + 0.1
Mole Fraction of KCl = 0.2

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Question 3 of 7

You need to prepare a solution of Sodium Chloride in water to contain Sodium Chloride at a mole fraction of 0.0060. If the volume of water (RMM 18.02, density 1 g/ml) used is 500 ml, how many grams of Sodium Chloride do you need? Answer to 3 decimal places.
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grams
The mass of Sodium Chloride needed is 9.798 grams.
  1. Find the mass of water used - using the given density of 1 g/ml:
    1 ml of water weighs 1g therefore 500 ml of water weigh 500 x 1 g ie 500 g
  2. Find how many moles of water there are.
    Moles of water = Mass / RMM = 500 / 18.02 = 27.7469
  3. Find the mole fraction of water.
    Mole fraction of water = 1 - Mole fraction of NaCl = 1 - 0.0060 = 0.994
  4. Find the total number of moles.
    Total number of moles = Number of Moles of Water = 27.7469 = 27.914386
    Mole Fraction of Water        0.994
  5. Find the moles of NaCl and the mass of NaCl.
    Number of Moles of NaCl = Mole Fraction x Total Moles = 0.0060 x 27.914386 = 0.167486
    Mass of NaCl = Moles x RMM = 0.167486 x 58.5 g = 9.7979 g
    Mass of NaCl = 9.798 g to 3 dec pl
    RMM NaCl = 58.5
  1. Find the mass of water used. Use the given density.
  2. Find how many moles of water are used.
  3. Find the mole fraction of water.
  4. Find the total number of moles.

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Question 4 of 7

How many moles are there in a solution if the solution contains 2 components only, 1.5 grams of Sodium Hydroxide and water at a mole fraction of 0.9975?

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moles
There are 15 moles altogether.

RMM NaOH = 40.0

  1. Find the mole fraction of Sodium Hydroxide.
    Mole fraction of Sodium Hydroxide = 1 - Mole Fraction of Water = 1- 0.9975 = 0.0025g
  2. Find the number of moles of Sodium Hydroxide
    Moles of Sodium Hydroxide = Mass / RMM = 1.5 / 40.0 = 0.0375 moles
  3. Find the total number of moles.
    Total number of moles = Number of Moles of NaOH
    Mole Fraction of NaOH
    Total number of moles = 0.0375
    0.0025
    Total number of moles = 15

Find the mole fraction of Sodium Hydroxide.

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Question 5 of 7

A solution is made of Sodium Acid Phosphate BP (RMM 156.0) and water (RMM 18.02). The solution contains 6.4 grams of Sodium Acid Phosphate BP in 200 grams of the solution. What is the mole fraction of Sodium Acid Phosphate BP? Answer to 5 decimal places.
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The mole fraction of Sodium Acid Phosphate is 0.00380.
  1. Find the mass of water in 200 grams of the solution.
    200 g of solution contains 6.4 g of Sodium Acid Phosphate BP
    Therefore there are 200 - 6.4 g ie 193.6 g of water in the 200 g of solution.
  2. Find the number of moles of water.
    Moles of water = mass / RMM = 193.6 / 18.02 = 10.743618 moles
  3. Find the number of moles of Sodium Acid Phosphate BP.
    Moles of Sodium Acid Phosphate BP = mass / RMM = 6.4 / 156.0 = 0.0410256 moles
  4. You can now find the mole fraction of Sodium Acid Phosphate BP
    Mole Fraction of SAP BP =      Moles of SAP BP    
    Total Number of Moles
    Mole Fraction of SAP BP =           0.0410256         
    10.743618 + 0.0410256
    Mole Fraction of SAP BP = 0.003804 = 0.00380 to 5 dec places
  1. Find the mass of water in 200 grams of the solution.
  2. Find the number of moles of water
  3. Find the number of moles of Sodium Acid Phosphate BP

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Question 6 of 7

A solution is made of Succinic Acid (RMM 118.0) dissolved in absolute Ethanol (RMM 46.0). There are 5.9 g of Succinic Acid in 100 ml of solution and the solution has a density of 0.820 g/ml. What is the mole fraction of Succinic Acid in the solution? Answer to 4 decimal places.

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The mole fraction of Succinic Acid is 0.0293.
  1. Find the moles of Succinic Acid.
    Moles of Succinic Acid = Mass / RMM = 5.9 / 118.0 = 0.05 moles
  2. Find the mass of the solution used - use the given density of 0.820 g/ml.
    1 ml of solution has a mass of 0.820 g. Thus:
    100 ml of solution has a mass of 100 x 0.820 g ie 82 g
  3. Find the mass of Absolute Ethanol present in 100 ml or 82 g of solution.
    Mass of Absolute Ethanol = Total Mass - Mass of Succinic Acid = 82 - 5.9 g = 76.1 g
  4. Find the number of moles of Absolute Ethanol present.
    Moles of Ethanol = Mass / RMM = 76.1 / 46.0 = 1.65434 moles
  5. Therefore the mole fraction of Succinic Acid is:
    Mole Fraction = Moles of Succinic Acid =           0.05            = 0.02933 = 0.0293 to 4 dec pl
    Total Number of Moles     0.05 + 1.65434
  1. Find the number of moles of Succinic Acid.
  2. Find the number of moles of Ethanol present.
    You will need to use the given density of 0.820 g/ml
    ie 1 ml weighs 0.82 g

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Question 7 of 7

Syrup BP consists of Sucrose (RMM 342.3) and water (RMM 18.02) and contains 222 grams of Sucrose in 250 ml of the syrup. If the density of the syrup is 1.332 g/ml, what is the mole fraction of Sucrose? Answer to 5 decimal places.
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The mole fraction of Sucrose is 0.09526.
  1. Find the moles of Sucrose.
    Moles of Sucrose = Mass / RMM = 222 / 342.3 = 0.6485539 moles
  2. Find the mass of the syrup used - use the given density of 1.332 g/ml
    1 ml of syrup has a mass of 1.332 g. Thus:
    250 ml of syrup has a mass of 250 x 1.332 g ie 333 g
  3. Find the mass of water present in 250 ml or 333 g of syrup.
    Mass of water = Total Mass - Mass of Sucrose = 333 - 222 g = 111 g
  4. Find the number of moles of water present.
    Moles of water = Mass / RMM = 111 / 18.02 = 6.1598224 moles
  5. Therefore the mole fraction of Sucrose is:
    Mole Fraction =        Moles of Sucrose       =           0.645539        
    Total Number of Moles         0.645539 + 6.1598224
    Mole Fraction = 0.095258 = 0.09526 to 5 dec pl
  1. Find the mass of syrup involved - use the density given.
  2. Find the mass of water present.
  3. Find the moles of water present

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