INTRODUCTION TO SOLUTIONSText 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

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.

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

Molar concentration = Moles Volume

or : c = n v

Where: c = molar concentration, in mol/Ln = number of molesv = 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 AlCl3 are contained in 350.0 mL of 0.250M AlCl3?

moles AlCl3 = 0.250 mol x 0.3500 L = 0.0875 mol L

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/L3) 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

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 250.0 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:

CI VI = CF VF

Where CI is the initial concentrationVI is the initial volumeCF is the final diluted concentrationVF 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 1000. mL water

AnswerGiven: 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

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

0.0878mol/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 255.5 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 106 ppb- 1 part in 109

[ppm] = (mass of solute) x106

(mass of solution)

[ppb] = (mass of solute) x109

(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 QuestionThe 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(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)    

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 Sr2+

Add NaCl (aq)

Ppt No Ppt

Solution Contained Lead (II) ions which were

precipitated as PbCl2

No Lead (II) ions were present