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

Incre

asi

ng

Increasing

Difference in Electronegativity

If the electronegativity difference is:

• less than 0.2 = bond is non-polar covalent

• is between 0.2 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 PairLone Pair

Structure & Shape of Water

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

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

Ionic Compounds in Water

Polar Molecules in WaterHydrogen Bonding

Polar Molecules (Sugar) in Water

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

𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑒𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 𝑜𝑓 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛

Percentage Concentration

• Percentage Weight by Volume

• Percentage Volume by Volume

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

•Molarity of a solution

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 needed to prepare a standard solution:

• Electronic balance

• Volumetric flask

Solution Preparation

Accurate Reading of a Volumetric Flask

Volumetric Graduated & Pipets and Bulb to transfer small quantities of

liquid

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

C1 x V1 = C2 x V2

•C1 = initial concentration

•V1 = initial volume

•C2 = final concentration

•V2 = final volume