INTRODUCTION TO SOLUTIONS Text 6.1-6.3: Page 266-290.
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Transcript of INTRODUCTION TO SOLUTIONS Text 6.1-6.3: Page 266-290.
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INTRODUCTION TO SOLUTIONSText 6.1-6.3: Page 266-290
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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.
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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
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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”
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Terminology
Things that are essentially completely insoluble in water are called immiscible
Things that are essentially completely soluble in water are called miscible
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Examples EVERYWHERE!
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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
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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.
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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
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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
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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?
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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.
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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
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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
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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
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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
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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
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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
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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
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Calculation Percent Concentration
Although concentration is expressed in mol/L, many common products use other units. These included: Volume % Mass % Mass Volume %
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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
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Calculating Volume % Example The concentration of acetic acid is
0.0878mol/L. If the density is 1.045g/mL, calculate the volume %.
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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)
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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.
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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).
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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%
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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)
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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)
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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)
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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
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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
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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
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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)
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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
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Chemical Analysis
Qualitative Identification of the
specific substances present
Can be accomplished by colour
Can be accomplished by a flame test
Sequential qualitative analysis
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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