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Introduction to solutions

Introduction to solutions. Text 6.1-6.3: Page 266-290. Learning Goals. By the end of this class, the students will be able to: Describe characteristics of solutions and Determine … Mass of solute Volume of solvent or Molarity of a solution

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Introduction to solutions

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  1. Introduction to solutions Text 6.1-6.3: Page 266-290

  2. Learning Goals • By the end of this class, the students will be able to: • Describe characteristics of solutions and • Determine… • Mass of solute • Volume of solvent or • Molarity of a solution • When given two of the three previous listed pieces of information.

  3. What is a Solution? • Solutions are homogeneous mixtures of two or more substances • Homogeneous: thoroughly mixed, even composition throughout • Solute dissolved in a solvent • Solute: substance being dissolved • Solvent: substance doing the dissolving

  4. Water: The Universal Solvent • Water is a common solvent • Water can dissolve a huge amount of compounds • Water is actually known as the “universal solvent”

  5. Terminology • Things that are essentially completely insoluble in water are called immiscible • Things that are essentially completely soluble in water are called miscible

  6. Examples EVERYWHERE!

  7. Molarity • Molar concentration is a number of moles in a 1L of solution • Represented by C • Units are mol/L or M • Also at times represented as the formula in square brackets • A dilute solution has a low concentration • A concentrated solution has a high concentration

  8. Some definitions • The CONCENTRATION of a substance in solution is the amount of the substance which exists in a given volume of the solution • A CONCENTRATED solution has a relatively high concentration (large amount of substance dissolved in a solution) • A DILUTE solution has a relatively low concentration (very little substance is dissolved in the solution) • A SATURATED solution contains the maximum amount of solute that can be dissolved in a particular quantity of solvent at equilibrium at a given temperature.

  9. What is Molarity? • The MOLAR CONCENTRATION of a substance in a solution that is the number of moles of the substance contained in 1 L of solution • Molar concentration is also known as MOLARITY • The unit symbol for “mol/L” is “M” • 1 mole is 6.02 x 10²³

  10. How to find molar concentration Molar concentration = Moles Volume or : c = n v Where: c = molar concentration, in mol/Ln = number of molesv = volume, in liters

  11. Calculations Involving Concentrations • C= n solute / V solvent • From this can determine mass or moles of solute, concentration or volume solvent Question 1: A box of apple juice has a fructose concentration of 12 g/ 100 mL. What is the mass of fructose in a 175mL glass of juice?

  12. Calculations Involving Concentrations Question 2: What volume of juice could a diabethic person drink if his sugar allowance for that beverage was 9.0 g? Again assume the concentration of sugar in the juice is 12g/ 100mL.

  13. Calculations:Moles, Volume, and Molarity 1) How many moles of AlCl3 are contained in 350.0 mL of 0.250M AlCl3? moles AlCl3 = 0.250 mol x 0.3500 L = 0.0875 molL 2) What volume of 2.40 M HCl can be made from 100.0 g of HCl? moles of HCl = 100.0g x 1 mol = 2.74 mol 36.5 g 2.74 mol = 1.14 L 2.40 mol/L 3) What is the molarity of the CaCl2 in a solution made by dissolving and diluting 15.00 g of CaCl2 x 6H2O in 0.500 L [CaCl2]=[CaCl2 x 6H2O] = 15.00g x 1 mol = 0.1369 M 0.5000 L 219.1g

  14. Standard Solutions • Solutions with very precise and specific molarities • To prepare need very specific measuring equipment and very specific volumes • Generally prepared in a very specific container for measurement called a volumetric flask

  15. How to Prepare a Standard Solution • Standard solutions can be prepared using many different solvents, but aqueous solution where water is the solvent are most common • Standard solutions are prepared using volumetric flasks • Flasks range from 10 mL to 2L with a graduation mark on the neck of the flask • when a 250 mL flask is filled to the graduation mark, it contains a volume of 250.0 mL ± 0.1 mL

  16. How to Dilute a Standard Solution • Occasionally you can be asked to prepare another solution of a lower concentration than the standard solution given • In this case, you will need to add water to the standard solution • This process is called dilution

  17. Dilution Calculations • The formula for dilution calculations is: CI VI = CF VF Where CI isthe initial concentration VIis the initial volume CFis the final diluted concentration VFis the final volume

  18. Dilution calculation example: A chemist starts with 50.0 mL of a 0.40 M NaCl solution and dilutes it to 1000 mL of water. What is the concentration of NaCl in the new solution? 50.0 mL of 0.40 M NaCl 1000. mL water

  19. Answer Given: CI = 0.40M, CF= ?, VI = 50.0mL, VF= 1000mL • Use CI VI = CF VF to solve for CF CI VI = CF VF (0.40 M) (50.0 mL) = (CF) (1000. mL) • Isolate for CF CF= (0.40 M) (50.0 mL) (1000. mL)   =0.020 M

  20. Calculation Percent Concentration • Although concentration is expressed in mol/L, many common products use other units. These included: • Volume % • Mass % • Mass Volume %

  21. Calculating Volume % • Volume % is used when two liquids are mixed to form a solution % solute by volume (v/v)= volume of solute x100% volume of solution For example: household vinegar has acetic acid in it, about 5%. This means that there is 5mL of acetic acid present in 100mL of vinegar solution

  22. Calculating Volume % Example • The concentration of acetic acid is 0.0878mol/L. If the density is 1.045g/mL, calculate the volume %.

  23. Calculating Mass % • Mass % is used for alloys (solid +solid) or (solid &liquid) % solute by = (mass of solute) x100% mass (m/m) (mass of solute + mass of solution)

  24. Calculating Mass % Example • A solution contains 5.3 g of potassium chloride in 255.5 g of water. Calculate the mass % of solute in this solution.

  25. Calculating Mass-Volume % • This concentration is used when the solute is a solid and the solvent is a liquid % m/v = (mass of solute) x100% (Volume of solution (mL)) • The concentration is written 3% m/v and its units are g/mL • Ie) in a 3% solution of iodine means 3 grams of iodine are dissolved in 100mL if solution (solvent is alcohol).

  26. Calculating Mass-volume % Example • Ordinary tea typically contains 3.3% m/v of caffeine. What mass of caffeine, in mg, will there be in a 150 mL cup of tea? Assume the volume of the solution is 100%

  27. Calculating Concentration in ppm & ppb • We use units of parts per million (ppm) & parts per billion (ppb) when measuring low concentration ppm- 1 part in 106 ppb- 1 part in 109 [ppm] = (mass of solute) x106 (mass of solution) [ppb] = (mass of solute) x109 (mass of solution)

  28. Example Calculation of [ ] in ppm & ppb • A study indicated that certain sea birds contained 25 ppb of DDT, (dichlorodiphenyltrichloroethane) which is one of the most well-known synthetic pesticides used. What mass of DDT in mg would be present if the sea bird has a mass of 4kg? (0.1mg)

  29. Practice Question The World Health Organization has set a maximum nitrate ion [ ] at 10ppm for infants and 50ppm for adults • If an infant had a mass of 4.0 kg, calculate the maximum allowed mass of nitrate ions? (40mg) • How about for an adult whose mass is 62kg? (3100mg)

  30. Soluble buuuuut…. • Even if soluble, will not be able to dissolve forever into solution • This is because at some point the solution will become saturated • When saturated no more solute can be dissolved into the solvent

  31. Saturated Solutions • Saturated solution contains the maximum amount of solute which can be dissolved into the solvent at a given temperature • Higher temperatures can dissolve more into it • Can look at solubility curves to determine at what point the solution will become saturated

  32. Random Notes… • Solids generally have higher solubility in water at high temperatures • Gases have a higher solubility in water at low temperatures • Pure elements generally have low solubility in water • Crystallization is caused by solvent evaporating out of solution

  33. Total Ionic and Net Ionic Equations Chemical Equation: Pb(NO3)2(aq)   +  2 NaCl(aq)→   PbCl2(s) +  2 NaNO3(aq) Total Ionic Equation: Pb2+(aq)+ 2NO3- (aq)   +  2 Na+(aq)+ 2Cl- (aq) →   PbCl2(s)  +  2 Na+(aq)+ 2NO3- (aq) Net Ionic Equation: Pb2+(aq)+ 2Cl- (aq) →    PbCl2(s)

  34. Chemical Analysis • Quantitative • Measurement of the quantity of the substance present • i.e. blood alcohol test • Stoichiometry problems • Will work on this more next day

  35. Chemical Analysis • Qualitative • Identification of the specific substances present • Can be accomplished by colour • Can be accomplished by a flame test • Sequential qualitative analysis

  36. Sequential Qualitative Analysis Solution may contain Pb2+ and/or Sr2+ Add NaCl(aq) Ppt No Ppt Solution Contained Lead (II) ions which were precipitated as PbCl2 No Lead (II) ions were present

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