Solutions & Solubility
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Transcript of Solutions & Solubility
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Solutions & Solubility
SCH3U
Chapter 6
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Chemistry Literature Connection
• “Water does not resist. Water flows. When you plunge your hand into it, all you feel is a caress. Water is not a solid wall, it will not stop you. But water always goes where it wants to go, and nothing in the end can stand against it. Water is patient. Dripping water wears away a stone. Remember that, my child. Remember you are half water. If you can't go through an obstacle, go around it. Water does.” ― Margaret Atwood, The Penelopiad
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Remember: Periodic Trends - Electronegativity
• Electronegativity = a number that describes the ability of an atom to attract electrons
•More electronegative = stronger pull on electrons being shared
• Less electronegative = weaker pull on electrons being shared
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Trend: Electronegativity
Incre
asi
ng
Increasing
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Difference in Electronegativity
If the electronegativity difference is:
• less than 0.4 = bond is non-polar covalent
• is between 0.4 and 1.6 = bond is polar covalent
• is greater than 1.7 = bond is ionic
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Types of Bonds
• Non-Polar Covalent = the attractive forces between two atoms that results when electrons are equally shared by the atoms with similar electronegativities
• Polar Covalent = a covalent bond formed between atoms with significantly different electronegativities resulting in unequal sharing of electrons
• Ionic = a bond formed due a large difference in electronegativity between atoms resulting in a complete transfer of electrons
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Comparison…
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Non-Polar versus Polar Covalent
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Structure & Shape of Water
Lone PairLone Pair
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Structure & Shape of Water
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Polarity of Water Molecules
Electronegativity differenceO = 3.5H = 2.13.5 – 2.1 = 1.4
Recall: between 0.2 and 1.6 = bond is polar covalent
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Polarity of Water Molecules
Dipole moment =measure the polarity of a chemical bond, occurs whenever there is a separation of positive and negative charges
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Hydrogen Bonding
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Ionic Compounds in Water
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Ionic Compounds in Water
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Polar Molecules in WaterHydrogen Bonding
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Polar Molecules (Sugar) in Water
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Polar Molecules (Sugar) in Water
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Non-Polar Molecules in Water
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“like dissolves like”
• Polar substances dissolve in polar solutions
•Non-polar substances dissolve in non-polar solutions
• In other words:
• like-polarity substances dissolve in each other
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Concentration =
Solution Concentration
𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛
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Percentage Concentration
• Percentage Weight by Volume
• Percentage Volume by Volume
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Very Low Concentrations
• Parts per million (ppm) = units used for very low concentrations
• Used for very dilute solutions
• Example:
• Toxic substances found in the environment
• Chlorine in a swimming pool
• Metals in drinking water
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Molar Concentrations
•Molar Concentrations (C)= the amount of solute, in moles, dissolved in one liter of solution
C = n/v
•Units = mol/L = M
•Molarity of a solution
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Solution Concentration• Dilute = having a relatively small quantity of
solute per unit volume of solution
• Concentrated = having a relatively large quantity of solute per unit volume of solution
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Making Solutions…
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Solution Preparation
• Standard Solution = a solution for which the precise concentration is known
• Used in research laboratories and industrial processes
• Used in chemical analysis and precise control of chemical reactions
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Equipment:
• Electronic balance precise measurement of solids
• Pipets (pipettes) precise measurement of liquids
• Volumetric flask calibrated to contain a precise volume at a particular temperature, used for precise dilutions and preparation of standard solutions
Preparing a Standard Solution
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Accurate Reading of a Volumetric FlaskBend down to see the meniscus
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Pipets and Bulb/Pump to transfer small quantities of liquid
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Volumetric Pipet
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Serological (Blow Out) Pipet
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Mohr (Graduated) Pipet
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Automatic Dispensers
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Micropipets – Dispense µL (microliters)
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Preparing a Solution by Dilution
• Dilution = the process of decreasing the concentration of a solution, usually by adding more solvent
• Stock Solution = a solution that is in stock or on the shelf (i.e., available); usually a concentrated solution
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Preparation of a Solution of Known Concentration by Diluting a Stock
Solution
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Preparation of a Solution of Known Concentration Using a Solid Solute
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Calculating the New Concentration of the Diluted Solution
C1 x V1 = C2 x V2
•C1 = initial concentration
•V1 = initial volume
•C2 = final concentration
•V2 = final volume
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Sample Problem
• Water is added to 0.200L of 2.40mol/L NH3(aq)
cleaning solution, until the final volume is 1.000L. Find the molar concentration of the final, diluted solution.
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Solubility
• Solubility = a property of a solute; the concentration of a saturated solution of a solute in a solvent at a specific temperature and pressure
• Saturated solution = a solution containing the maximum quantity of a solute at specific temperature and pressure conditions• No more solute will dissolve, visible solids in solution
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Unsaturated vs. Saturated
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Unsaturated vs. Saturated
• Unsaturated solution = a solution containing less than maximum quantity of a solute at specific temperature and pressure conditions
• Supersaturated solution = a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances
• Make by heatinga solution to dissolve more solute, then returning the solute to a lower temperature
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Supersaturated Solution
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Solubility of Solids• Solubility of a substance changes with
temperature
• Solids show a higher solubility at higher temperatures
• Solubility Curve = a graph of solubility and temperature of a solution
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Solubility Curve of Solids
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Solubility of Gases• Higher solubility at lower temperatures
• Think: Pop
• Can of pop from the fridge Gasses dissolved
vs
• Can of pop at room temperature Gasses escape
• Can of pop is also stored under pressure
• Increased pressure = increased solubility
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Solubility of Gases
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Solubility of Liquids
•Difficult to generalize about, but:
• For polar liquids solubility usually increases with increase in temperature
• Immiscible = two liquids that form separate layers instead of dissolving
•Miscible = liquids that mix in all proportions and have no maximum concentration
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Solubility Categories
• High solubility = with a maximum concentration at SATP (standard ambient temperature and pressure) of greater than or equal to 0.1mol/L
• Low solubility = with a maximum concentration at SATP of less then 0.1mol/L
• Insoluble = a substance that has a negligible solubility at SATP
• SATP = standard ambient temperature and pressure, = exactly 25°C and 100kPa
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Using a Solubility Table
• Solubility of ionic compounds
•Anions paired with particular cations have either:
• High solubility (equal or greater than 0.1mol/L)
OR
• Low solubility (less than 0.1mol/L)
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Solubility Table
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Reactions in Solution• If a chemical reaction results in the formation
of a compound which has low solubility the compound will not be dissolved in the solution and is said to precipitate out of solution
• Precipitate = the solid formed in a chemical reaction or by decreased solubility
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Net Ionic Equations• Total Ionic Equation = a chemical equation
that shows all high-solubility ionic compounds in their dissolved form
• Spectator = an entity such as an ion, that does not change or take part in a chemical reaction
• Net Ionic Equation = shows only the reacting species in a chemical reaction and does not include the spectator ions
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1.Write the balanced chemical equation with full chemical formulas for all reactants and products.
2.Using a solubility table, rewrite the formulas for all high-solubility ionic compounds as dissociated ions, to show the total ionic equation.
3.Cancel identical amounts of identical entities appearing on both reactant and product sides (spectator ions).
4.Write the net ionic equation, reducing coefficients if necessary.
Writing Net Ionic Equations
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Example: Net Ionic EquationDouble Displacement
Zinc metal and aqueous copper (II) sulfate react
1. Balanced Eqn: Zn(s) + CuSO4(aq) ZnSO4(aq) + Cu(s)
2. Total Ionic Eqn: Zn(s) + Cu2+ (aq)
+ SO42-
(aq) Zn2+(aq)
+So42-
(aq) + Cu(s)
3. Net Ionic Eqn: Zn(s) + Cu2+(aq)
Zn2+(aq) + Cu(s)
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Qualitative Analysis
• Qualitative Analysis = the identification of the specific substances present
• Describes a quality or change in matter that has no numerical value expressed
• Quantitative Analysis = the measurement of the quantity of a substance present
• Describes a quantity of matter or degree of change of matter
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• Colour of Solutions
• Colour of Flames
Qualitative Analysis by Colour
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Colours of Solutions & Flames
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Sequential Qualitative Chemical Analysis
• Qualitative Chemical Analysis = the identification of substances present in a sample; may involve several diagnostic tests
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Acids & Bases
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Unsaturated vs. Saturated
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Unsaturated vs. Saturated