INTRODUCTION TO SOLUTIONS Text : Page

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.

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

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”

Terminology  Things that are essentially completely insoluble in water are called immiscible  Things that are essentially completely soluble in water are called miscible

Examples EVERYWHERE!

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

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. 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.

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 10 ²³

Molar concentration = Moles Volume or : c = n v Where:c = molar concentration, in mol/L n = number of moles v = volume, in liters How to find molar concentration

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 ?

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.

Calculations: Moles, Volume, and Molarity 1) How many moles of AlCl 3 are contained in mL of 0.250M AlCl 3 ? moles AlCl 3 = mol x L = mol L 2) What volume of 2.40 M HCl can be made from 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 g of CaCl2 x 6H2O in L [CaCl2]=[CaCl2 x 6H2O] = 15.00g x 1 mol = M L 219.1g

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

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 mL ± 0.1 mL

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

Dilution Calculations The formula for dilution calculations is: C I V I = C F V F Where C I is the initial concentration V I is the initial volume C F is the final diluted concentration V F is the final volume

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 mL water

Answer Given: C I = 0.40M, C F = ?, V I = 50.0mL, V F = 1000mL  Use C I V I = C F V F to solve for C F C I V I = C F V F (0.40 M) (50.0 mL) = (C F ) (1000. mL)  Isolate for C F C F = (0.40 M) (50.0 mL) (1000. mL) =0.020 M

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

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

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

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)

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

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).

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%

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 10 6 ppb- 1 part in 10 9 [ppm] = (mass of solute) x10 6 (mass of solution) [ppb] = (mass of solute) x10 9 (mass of solution)

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)

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

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

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

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

Total Ionic and Net Ionic Equations Chemical Equation: Pb(NO 3 ) 2(aq) + 2 NaCl (aq) → PbCl 2 (s) + 2 NaNO 3 (aq) Total Ionic Equation: Pb 2+ (aq) + 2NO 3 - (aq) + 2 Na + (aq) + 2Cl - (aq) → PbCl 2(s) + 2 Na + (aq) + 2NO 3 - (aq) Net Ionic Equation: Pb 2+ (aq) + 2Cl - (aq) → PbCl 2(s)

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

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

Sequential Qualitative Analysis Solution may contain Pb 2+ and/or Sr 2+ Add NaCl (aq) PptNo Ppt Solution Contained Lead (II) ions which were precipitated as PbCl 2 No Lead (II) ions were present