Concentrations

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Concentrations

• Envr 1402

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Different Types of Solutions

• Percent Solutions
• Weight/weight solutions (w/w)
• Weight/volume solutions (w/v)
• Volume/volume solutions (v/v)
• Parts Solutions
• Parts per thousand (ppt)
• Parts per million (ppm)
• Parts per billion (ppb)
• Parts

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Weight/weight Percent Solutions

• These are primarily used in industry for
  commercial aqueous solutions such as nitric acid.
• (w/w) soln weight of solute x 100
• weight of solution
  (Equation 1)
• So, by using some algebra
• Weight of solute soln x weight of solution
• 
  (Equation 2)

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Example 1 (w/w) solutions

• You have 200g of a solution that contains 30g of
  hydrochloric acid (HCl), what percentage of your
  solution is made up of hydrochloric acid?
• soln 30g of HCl x 100 15
• 200g of solution
• So, your solution is 15 hydrochloric acid.

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Example 2 (w/w) solutions

• How would you make 150g of a 25 solution of
  nitric acid in water?
• 25g nitric acid x 150g solution 37.5g
• 100g of solution
• So, you would need 37.5g of nitric acid and
  112.5g of water to make 150g of 25(w/w) solution
  of aqueous nitric acid.

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Weight/volume Percent Solutions

• Commonly used when a solute is solid.
• i.e. salt in water
• (w/v) soln weight of solute x 100
• volume of solution
  (Equation 3)
• So, using some algebra
• weight of solute soln x volume of solution
• 
  
  (Equation 4)

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Example 3 (w/v) solutions

• Suppose you have 70g of sodium chloride salt
  (NaCl) in 250mL of water. Express this as a
  (w/v) solution.
• soln 70g NaCl x 100 28
• 250mL water
• So, you have a 28 NaCl solution.

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Example 4 (w/v) Solution

• How would you make 200mL of a 15 salt in water
  solution?
• 15g salt x 200mL soln 30g salt
• 100 mL water
• So, you would put 30g of salt in a flask and add
  water up to 200mL. (BTV)

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Volume/volume Percent Solutions

• Primarily used when the solute is a liquid.
• i.e. ethanol in water
• (v/v) soln volume of solute x 100
• volume of solution
  (Equation 5)
• So, using some algebra
• volume of solute soln x volume of solution
• 
  
  (Equation 6)

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Example 5 (v/v) solutions

• Suppose you have 9mL of ethanol in 25mL of
  solution. Express this as a (v/v) solution.
• 9mL ethanol x 100 36
• 25mL soln
• So, you have a 36 ethanol solution.

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Example 6 (v/v) solutions

• How would you make 500mL of a 30 vinegar in
  water solution?
• 30mL vinegar x 500mL soln 150mL
• 100mL soln
• So, you would place 150mL of vinegar in a flask
  and bring to level (500mL) with water.

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Parts Per Million (ppm)

• One part in one million parts
• i.e. 1g/1,000,000g or 1g/1 x 106g
• 1ppm 1mg/L
• Why you ask?

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Why is 1ppm 1mg/L ?

• 1ppm 1mg/1,000,000mg
• Convert mg to kg
• 1000mg 1g and 1000g 1kg
• so 1,000,000mg 1kg
• So, 1mg/1,000,000mg 1mg/1kg
• Convert kg to L
• The conversion unit is 1kg 1L
• So, 1mg/1kg 1mg/1L 1mg/L
• Therefore, 1ppm 1mg/L

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Parts Per Billion (ppb)

• 1 part in 1 billion parts
• i.e. 1g in 1,000,000,000g

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Example 7 parts conversions

• Convert 5 ppm to mg/mL
• 1. 5ppm 5g/1,000,000g
• Now convert g to mL (1g 1mL)
• 2. 5g/1,000,000g 5g/1,000,000mL
• Now convert g to mg (1g 1,000mg)
• 3. 5g/1,000,000mL 5,000mg/ 1,000,000mL
• Now simplify
• 4. 5,000mg/1,000,000mL 5mg/1,000mL
  0.005mg/mL

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More Parts Solutions

• Used like a cooking recipe when a solution is
  made up of multiple components.

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Example 8 more parts solutions

• You have a recipe that calls for 1 part ethanol,
  3 parts methanol, and 6 parts chloroform. How
  would you prepare 45mL of this solution?

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Example 8 continued

• First, add up all the parts
• 1 3 6 10
• Then calculate how much of each component you
  need.
• 1/10 x 45mL 4.5mL ethanol
• 3/10 x 45mL 13.5mL methanol
• 6/10 x 45 27mL chloroform
• So, you need 4.5mL of ethanol, 13.5mL of
  methanol, and 27mL of chloroform.
• Check yourself If you add up all the parts of
  the solution, you should end up with 45mL.