unit 8, part i - solutions and solubility. key terms anion - a negatively charged ion aqueous...
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UNIT 8, PART I - SOLUTIONS AND SOLUBILITY
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KEY TERMS
Anion - A negatively charged ion
Aqueous Solution - A solution where water is mixed with something to make a solvent
Cation - A positively charged ion
Concentration - The amount of solute per unit volume of solution Dilution - Weakening or reducing the concentration Molarity (M) - Concentration measured by the number of moles of solute per liter of solution Insoluble - Incapable of being dissolved
Polarity - A separation of electric charge leading to a molecule having an electric dipole Saturated Solution - A solution that contains the maximum amount of solute at a given
temperature
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KEY TERMS
Solubility - The quantity of a particular substance that can dissolve in a particular solvent
Solubility Curve - A graph showing the relationship between solubility and temperature
Soluble - Able to be dissolved
Solute - The dissolved matter in a solution
Solvent - Able to dissolve other substances Unsaturated Solution - A solution that contains less than the
maximum amount of solute at a given temperature
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WATER AS A SOLVENT
Water is the most effective solvent
Water will dissolve many ionic compounds and most polar covalent compounds
Water is not effective as a solvent for non-polar covalent compounds
Effectiveness of water is because water is highly polar with hydrogen bonds Used courtesy of: http://www.volusia.org/services/public-works/water-resources-and-utilities/
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WATER AS A SOLVENT – POLARITY (IT IS THE KEY)
Image used courtesy of: http://www.ecfs.org/projects/prepole/MARINE%20BIOLOGY%2012/Chapter%20Readings/Ch%201%20Oceanography/Chapter%201%20Notes.htm
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WATER AS A SOLVENT- HYDROGEN BONDING
Image used courtesy of CINCH ® Learning
The powerful attraction between an oxygen atom from one water molecule and a hydrogen atom from another water molecule
Image used courtesy of: http://www.glogster.com/arooke2/hydrogen-bonds/g-6m99vd692fc7hgidt985ta0?old_view=True
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SOLUBILITY
The ability to dissolve a solute in a solvent to form a solution, a homogeneous mixture
Solute – The matter dissolved in a solvent
Solvent – The matter in which a solute is dissolved
Solution – Homogeneous mixture
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TYPES OF SOLUTIONS
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FACTORS AFFECTING SOLUBILITY
It is all about polarity!! The nature of the solvent affects solubility
Like Dissolves Like
Ionic compounds, if they are soluble, dissolve in polar solvents
Polar molecular (covalent) compounds dissolve in polar solvents
Non-polar molecular (covalent) compounds dissolve in non-polar solvents
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FACTORS AFFECTING SOLUBILITY
Factors affecting the solubility of solids and liquids Temperature
Generally, as temperature increases, the solubility of solids and liquids increases
Factors affecting the solubility of gases Temperature
Generally, as temperature increases, the solubility of gases decreases
Pressure
Generally, as pressure increases, the solubility of gases increases
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SUMMARY OF FACTORS AFFECTING SOLUBILITY
Temperature
As temperature ↑, solubility of liquids and solids↑
As temperature ↑, solubility of gases↓
Pressure
As pressure ↑, solubility of liquids and solids is unaffected
As pressure ↑, solubility of gases ↑
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SUMMARY OF FACTORS AFFECTING SOLUBILITY
Nature of Solvent Generally the nature of the solvent will determine what kinds
of matter will dissolve in it. Polar solvents (such as water) will generally dissolve polar compounds.
Non‐polar compounds will generally dissolve non‐polar compounds.
Ionic compounds, if they are soluble, dissolve in polar solvents
Polar molecular (covalent) compounds dissolve in polar solvents
Non‐polar molecular (covalent) compounds dissolve in non‐polar solvents
LIKE DISSOLVES LIKE!
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CONCENTRATION AND SOLUBILITY
The amount of solute affects both solubility and dissolving rate.
A solvent can only dissolve so much solute.
As the concentration increases, the ability to dissolve more decreases
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DISSOLVING RATE
The rate at which the solute dissolves in the solvent
As Kinetic Energy increases, dissolving rate increasesAs Kinetic Energy decreases, dissolving rate decreases
As the number of collisions increases, dissolving rate increases
As the number of collisions decreases, dissolving rate decreases
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DISSOLVING RATE
Factors affecting dissolving rateTemperature
As temperature increases, dissolving rate increases
Surface Area As surface area increases, particle size decreases As surface area increases, dissolving rate increases
Agitation As agitation increases, dissolving rate increases
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TEMPERATURE AND DISSOLVING RATE
Since temperature is a measurement of the average kinetic energy, changing the temperature by adding or removing heat will change the rate of dissolving. Increasing the temperature speeds up the movement of its particles
The change in temperature will affect both the number of collisions and the probability that as particles collide the solute will dissolve in the solvent. Allows for more collisions between solute particles and solvent particles
Used courtesy of: http://www.seriouseats.com/2012/10/ask-the-food-lab-on-hot-chocolate-and-whole-wheat.html
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SURFACE AREA AND DISSOLVING RATE Breaking a solid into smaller pieces greatly increases its surface
area
More solvent particles can come into contact with more particles of the solute corresponding to increased surface area
Rate of collisions increases as surface area increases
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AGITATION AND DISSOLVING RATE
Agitation is the result of an external force causing the motion of the solute and the solvent such that there is an increased chance of collision.
Stirring, Mixing, Shaking
As agitation speed increases, rate of dissolving increases
As the solvent moves around, more collisions occur between solvent and solute particles
Used courtesy of: http://www.pennlive.com/lehighvalley-generalent/index.ssf/2008/06/in_defense_of_koolaid.html
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SUMMARY OF FACTORS AFFECTING DISSOLVING RATES
As temperature ↑, dissolving rate ↑
As particle size ↓, surface area↑, dissolving rate ↑
As agitation ↑, dissolving rate ↑
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CONCENTRATION AND SOLUBILITY
The amount of solute affects both solubility and dissolving rate.
A solvent can only dissolve so much solute.
As the concentration increases, the rate at which it will dissolve decreases.
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CONCENTRATION OF SOLUTIONS Concentration – the degree to which a solution contains the maximum
amount of solute.
Directly related to density
Qualitative
Uses terms saturated and unsaturated to reference the amount of solute dissolved in the solvent
Quantitative
Molarity – the number of moles dissolved in one liter of solution
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SOLUTIONS AND SATURATION• Saturated Solution – A solution is considered saturated when it contains the
maximum amount of solute given the volume and environmental conditions of the solvent.
• Unsaturated Solution – Any solution into which more solute can be dissolved is unsaturated. • An unsaturated solution that is close to the point of saturation is referred to as
“concentrated”.• An unsaturated solution well below the point of saturation is referred to as “dilute”.
• Super‐Saturated Solution – Any solution that contains more dissolved solute than it could contain under normal conditions is super‐saturated. • A beverage with carbonated water is a supersaturated solution. It is packaged into
cans or bottles under conditions of high pressure. When the can or bottle is later opened, the carbon dioxide bubbles out of solution under the lower pressure.
• Rock candy is made using a supersaturated solution of sugar and allowing the sugar crystals to slowly form on a string dipped in sugar.
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SOLUTIONS & SATURATION
Unsaturated Saturated Supersaturated
Definition Contains less than the maximum amount of solute. More solute can dissolve in the solvent
Contains the maximum amount of solute. No more solute will dissolve in the solvent. If there is extra undissolved solute, it will settle to the bottom of the container.
Contains more dissolved solute than the maximum under normal conditions
Solubility Curve Below the saturation line
On the saturation line Above the saturation line
Can you Dissolve More Solute?
Yes No No, it is already past saturation point
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Imaged used courtesy of: http://www.mts.net/~alou/Chemistry%2011/Unit%204%20-%20Solutions%20Lessons/Lesson%203%20-%20Factors%20Affecting%20Solubility.htm
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SOLUBILITY CURVES Show the amount of solute that can dissolve in a solvent under
normal circumstances at a given temperature
The line for a given element on a set of solubility curves is called the saturation line
Comparisons are made using the line for a given compound Under the curve – the solution is unsaturated Above the curve without excess – the solution is supersaturated Above the curve with excess – the solution is saturated On the curve – the solution is saturated
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SOLUBILITY CURVES
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QUANTITATIVE SOLUBILITY: MOLARITY
Measured as moles of solute per liter of solution
Molarity = Moles of solute Liters of solution
M = Moles Liter
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MOLARITY EXAMPLE
116.88 grams of NaCl are dissolved in 1.5 liters of solution. What is the molarity of this solution?
First, convert grams of NaCl to moles NaCl
Found by dividing 116.88g by the molar mass of NaCl, 58.44 g/mol116.88g NaCl is 2.00 moles of NaCl
Next, divide moles solute by liters of solution
2.00 moles NaCl = 1.33 mol NaCl/L = 1.33 M NaCl 1.5 L
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DILUTION What does it mean to dilute a solution? Solutions can be diluted simply by adding water and leaving the amount of
solute unchanged What happens to molarity when a solution is diluted?
More water has been added, so the total volume of solution is greater but the amount of solute is the same
Molarity will decrease!
We use the following equation to perform dilution calculations:M1V1=M2V2
M1=Initial molarity
V1= Initial volume
M2= Final molarity
V2=Final volume
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DILUTION EXAMPLE What would be the resulting molarity of 2.5 L solution when the starting solution had a molarity of 6.00 M and a volume of 417 mL?
M1= 6.00 mol/L M2= ??
V1= 417 mL V2= 2500 mL
M1V1=M2V2
(6.00 mol/L)(417 mL) = (M2)(2500 mL)
(M2) = (6.00 mol/L)(417 mL)
(2500 mL)
M2 = 1.00 mol/L
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DISSOCIATION AND DISPERSION
Dissociation – When ionic compounds dissolve, they separate into the ions that were bonded together.
Example: Potassium sulfate will dissociate into potassium ions and sulfate ions. K2SO4 → 2K1+ + SO4
2-
More examples of dissociation: NaCl → Na1+ + Cl 1-
MgCl2 → Mg2+ + 2 Cl1-
Al2(SO4)3 → 2 Al3+ + 3SO42-
Dispersion – When complete dispersion occurs, the molecules of the solute are uniformly mixed with the molecules of the solvent. This occurs with covalent compounds.
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ELECTROLYTIC SOLUTIONS
Electrolytic solutions conduct an electrical current
Ions dissociate when dissolved in water
Ions, because they are charged particles, act as a path for the flow of electricity
The more ions present, the more electrolytic the solution is
Non-electrolytic solutions do not conduct an electrical current
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ELECTROLYTIC SOLUTIONS
Soluble Ionic Solute
Non-Soluble Ionic Solute
Non-Soluble Covalent Solute
Electrolyte Yes No No
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CONTROLLING ELECTROLYTIC SOLUTIONS
In order to increase the electrolytic properties of a solution you must increase the concentration of ions present in the solution
Reduce the volume of the solution while maintaining the amount of electrolytic solute
Increase the amount of electrolytic solute without modifying the volume
Using a different electrolytic solute which produces more ions when it dissociates
In order to decrease the electrolytic properties of a solution you must decrease the concentration of ions present in the solution
Dilute the electrolytic solution
Using a different electrolytic solute which produces less ions when it dissociates