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Solution Concentration

Solution Concentration. Remember: Periodic Trends - Electronegativity. Electronegativity = a number that describes the ability of an atom to attract electrons More electronegative = stronger pull on electrons being shared Less electronegative = weaker pull on electrons being shared.

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Solution Concentration

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  1. Solution Concentration

  2. Remember: Periodic Trends - Electronegativity • Electronegativity = a number that describes the ability of an atom to attract electrons • More electronegative = stronger pull on electrons being shared • Less electronegative = weaker pull on electrons being shared

  3. Trend: Electronegativity Increasing Increasing

  4. Difference in Electronegativity If the electronegativity difference is: less than 0.4= bond is non-polar covalent is between 0.5 and 1.6 = bond is polar covalent is greater than 1.7= bond is ionic

  5. Types of Bonds • Non-Polar Covalent = the attractive forces between two atoms that results when electrons are equally sharedby the atoms with similar electronegativities • Polar Covalent = a covalent bond formed between atoms with significantly different electronegativitiesresulting in unequal sharing of electrons • Ionic= a bond formed due a large difference in electronegativity between atoms resulting in a complete transfer of electrons

  6. Comparison…

  7. Non-Polar versus Polar Covalent

  8. Solution and Concentration How can we express the amount of solute to solvent in a solution? • This is called the concentration • a measure of the number of particlesof the solute in the solvent • Concentration =

  9. Ways to express concentration 3 ways of expressing concentration • Percentages • PPM or PPB concentrations • molar concentrations and mass concentrations

  10. Percentage Concentration • % (w/w) = • W is weight same as mass • % (w/v) = • % (v/v) =

  11. Everyday Examples • Vinegar is 5% v/v acetic acid • 5 mL of CH3COOH in 100 mL vinegar • Hydrogen peroxide is 3% m/v • 3 g of H2O2 per 100 mL of solution • Yogurt is 2% m/m • 2 g of milk fat per 100 g yogurt

  12. Examples • % V/V = 4.1 L / 55 L = 7.5% V/V • % W/V = 16 g / 50 mL = 32% W/V • % W/W = 1.7 g / 35.0 g = 4.9% W/W More practice • What is the % W/W of copper in an alloy when 10 g of Cu is mixed with 250 g of Zn? • What is approximate % V/V if 30 mL of pure ethanol is added to 250 mL of water? • What is the %W/W if 8.0g copper is added to enough zinc to produce 100 g of an alloy

  13. %m = 3.5 g CoCl2 100g H2O = 3.5% (m/m) % Concentration: % Mass Example 3.5 g of CoCl2 is dissolved in 100mL solution. Assuming the density of the solution is 1.0 g/mL, what is concentration of the solution in % mass?

  14. Low concentrations • For very dilute solutions, weight/weight (w/w) and weight/volume (w/v)concentrations are sometimes expressed in parts per million (ppm). • Example: • Toxic substances found in the environment • Chlorine in a swimming pool • Metals in drinking water • Parts per million also can be expressed • as milligrams per liter (mg/L) (w/v) • As milligram per kilogram (mg/Kg) (w/w)

  15. PPM learning check 1. Question: A solution has a concentration of 1.25g/L. What is its concentration in ppm? • Convert the mass in grams to a mass in milligrams: 1.25g = 1.25 x 1000mg = 1250mg • Re-write the concentration in mg/L = 1250mg/L = 1250ppm 2. Question: 150mL of an aqueous sodium chloride solution contains 0.0045g NaCl. Calculate the concentration of NaCl in parts per million (ppm). ppm = mass solute (mg) ÷ volume solution (L) mass NaCl = 0.0045g = 0.0045 x 1000mg = 4.5mg  volume solution = 150mL = 150 ÷ 1000 = 0.150L concentration of NaCl = 4.5mg ÷ 0.150L = 30mg/L = 30ppm

  16. Molar concentration • is able to compare the amount of solute (moles) dissolved in a certain volume of solution. • Molar concentration (mol/L) or also called Molarity (M) = Moles of solute (n)/Volume of solution (V MUST be in litres) • is the number of moles of solute in one litre of a solution. We use "M" to denote molar concentration and it has the units of"mol/L". • C = n / V • n = C x V

  17. Concentration: Molarity Example If 0.435 g of KMnO4 is dissolved in enough water to give 250. mL of solution, what is the molarity of KMnO4? As is almost always the case, the first step is to convert the mass of material to moles. MM = 158.0 g/mol(39+55+(4X16) n= m/MM 0.435 g KMnO4 / 158.0 g/ mol = 0.00275 mol KMnO4 Now that the number of moles of substance is known, this can be combined with the volume of solution — which must be in liters — to give the molarity. Because 250. mL is equivalent to 0.250 L . Molarity KMnO4 = 0.00275 mol KMnO4 = 0.0110 Mol/L = M 0.250 L solution

  18. Molarity learning check • How many moles of H2SO4 are there in 250mL  of a 0.8M sulphuric acid solution? • If 20g of NaOH is dissolved in sufficient water to produce 500 mL of solution, calculate the molar concentration in molarity. Questions • What is the molarity of the solution formed by dissolving 80 g of sodium hydroxide (NaOH) in 500 mLs of water? (Ar's: Na=23, O=16, H=1) Ans = 4 M • What is the molarity of the solution formed by dissolving 9.8 g of sulphuric acid (H2SO4) in 1000 cm3 of water? (Ar's: H=1, S=32, O=16) Ans = 0.1 M 3. What mass (g) of hydrogen chloride (HCl) is needed to make up 500cm3 of a solution of concentration 0.2mol/L? (Ar's: H=1, Cl=35.5) Ans = 3.65g

  19. Making Solutions…

  20. Solution Preparation • Standard Solution = a solution for which the precise concentration is known • Used in research laboratories and industrial processes • Used in chemical analysis and precise control of chemical reactions

  21. Preparing a Standard Solution Equipment: • Electronic balance  precise measurement of solids • Pipets (pipettes)  precise measurement of liquids • Volumetric flask  calibrated to contain a precise volume at a particular temperature, used for precise dilutions and preparation of standard solutions

  22. Accurate Reading of a Volumetric FlaskBend down to see the meniscus

  23. Pipets and Bulb/Pump to transfer small quantities of liquid

  24. Volumetric Pipet

  25. Serological (Blow Out) Pipet

  26. Mohr (Graduated) Pipet

  27. Automatic Dispensers

  28. Micropipets – Dispense µL (microliters)

  29. Preparing a Solution by Dilution • Dilution = the process of decreasing the concentration of a solution, usually by adding more solvent • Stock Solution = a solution that is in stock or on the shelf (i.e., available); usually a concentrated solution

  30. Preparation of a Solution of Known Concentration by Diluting a Stock Solution

  31. Preparation of a Solution of Known Concentration Using a Solid Solute

  32. Calculating the New Concentration of the Diluted Solution C1 x V1 = C2 x V2 C1 = initial concentration V1 = initial volume C2 = final concentration V2 = final volume

  33. Sample Problem • Water is added to 0.200L of 2.40mol/L NH3(aq) cleaning solution, until the final volume is 1.000L. Find the molar concentration of the final, diluted solution.

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