Solutions & Solubility SCH3U Chapter 6

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

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

Trend: Electronegativity Increasing

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

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

Comparison…

Non-Polar versus Polar Covalent

Structure & Shape of Water Lone Pair

Structure & Shape of Water

Polarity of Water Molecules Electronegativity difference O = 3.5 H = – 2.1 = 1.4 Recall: between 0.2 and 1.6 = bond is polar covalent

Polarity of Water Molecules Dipole moment =measure the polarity of a chemical bond, occurs whenever there is a separation of positive and negative charges

Hydrogen Bonding

Ionic Compounds in Water

Polar Molecules in Water Hydrogen Bonding

Polar Molecules (Sugar) in Water

Non-Polar Molecules in Water

“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

Concentration = Solution Concentration

Percentage Concentration

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

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

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

Making Solutions…

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

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

Accurate Reading of a Volumetric Flask Bend down to see the meniscus

Pipets and Bulb/Pump to transfer small quantities of liquid

Volumetric Pipet

Serological (Blow Out) Pipet

Mohr (Graduated) Pipet

Automatic Dispensers

Micropipets – Dispense µL (microliters)

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

Preparation of a Solution of Known Concentration by Diluting a Stock Solution

Preparation of a Solution of Known Concentration Using a Solid Solute

Calculating the New Concentration of the Diluted Solution C 1 x V 1 = C 2 x V 2 C 1 = initial concentration V 1 = initial volume C 2 = final concentration V 2 = final volume

Sample Problem Water is added to 0.200L of 2.40mol/L NH 3(aq) cleaning solution, until the final volume is 1.000L. Find the molar concentration of the final, diluted solution.

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

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

Supersaturated Solution

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

Solubility Curve of Solids

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

Solubility of Gases

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

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

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)

Solubility Table

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

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

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

Example: Net Ionic Equation Double Displacement Zinc metal and aqueous copper (II) sulfate react 1. Balanced Eqn:Zn (s) + CuSO 4(aq)  ZnSO 4(aq) + Cu (s) 2. Total Ionic Eqn: Zn (s) + Cu 2+ (aq) + SO 4 2- (aq)  Zn 2+ (aq) +So 4 2- (aq) + Cu (s) 3. Net Ionic Eqn: Zn (s) + Cu 2+ (aq)  Zn 2+ (aq) + Cu (s)

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

Colour of Solutions Colour of Flames Qualitative Analysis by Colour

Colours of Solutions & Flames

Sequential Qualitative Chemical Analysis Qualitative Chemical Analysis = the identification of substances present in a sample; may involve several diagnostic tests

Acids & Bases

Unsaturated vs. Saturated