Advanced Chemistry NotesSolution Notes

Solutions

Solutions – homogeneous mixtures of two or more substances

• Made up of:– Solvent – substance that does the dissolving– Solute – substance being dissolved

• Examples of Solutions– Kool-Aide: water – solvent, sugar – solute– Pop: water – solvent, carbon dioxide – solute

Solutions

Types of Solutions • Liquid – Solid solution

– Ex: salt water

• Liquid – Liquid solution– Ex: hydrochloric acid and water

• Miscible – when two liquids mix• Immiscible – when two liquids will not mix

• Liquid – Gas solution– Ex: oxygen and water

SolutionsOther types of Solutions• Solid – Solid solutions

– Brass alloys

• Solid - Liquid solutions – Gold dissolves Mercury

• Solid – gas solutions – Palladium dissolves hydrogen

• Gas – Gas solution – air: O2, N2, Ar

Creating Solutions

The dissolving process consists of three steps

• Dissociation

• Solvation

• Diffusion

The Dissolving Process

The Dissolving Process (Ex: sugar and water)

1. Dissociation

• Attractive forces between solute molecules must be overcome.

• Water pulls sugar apart molecule by molecule

The Dissolving Process

2. Solvation

• Positive ends of solvent molecule attach to negative ends of solute molecule and vise versa.

• Water molecules surround and interact with sugar molecules.

• Water molecules remove sugar molecules from the crystal

– Dispersion and dipole forces are at work here

Solvation

The Dissolving Process

The Dissolving Process

• When the solvent is water the solvation process is called hydration.

The Dissolving Process

3. Diffusion• Random molecular movement spreads solute

through out the solution• Sugar molecules are evenly dispersed

throughout the water

Factors Influencing Dissolving

• Factors that influence that rate at which a substance dissolves– Temperature – Stirring – Large surface area of solute exposed to

solvent

• How does this relate to putting sugar in your coffee?

Solvent SelectivityWhat will and will not dissolve?

• G R of T Like dissolves Like

• Polar substances dissolves other polar substances– Polar – ionic and polar covalently bonded

compounds have dipoles• H2O and HCl

Solvent Selectivity

• Non-polar substances dissolve other non-polar substances– Non-polar compounds lack dipoles

• CO2 and N2

• Oil and Soap

• Exceptions to the rule– Chalk (CaCO3) does not dissolve in water –Why?

Both are polar.• Water has to be able to overcome chalks (CaCO3)

intermolecular attractive forces to dissolve it – it can’t

• Chalk (CaCO3) is to tightly bonded intermolecularly

Solubility

• How much solute can a substance hold?

• Unsaturated solution – the solvent could dissolve more solute under standard conditions

Solubility

• Saturated solution – when solvent can hold no more solute at a given temperature.– When solution is saturated some of the solute

remains at the bottom of the glass. Dissolving and precipitating occur at equal rates. This is called Dynamic Equilibrium.

– H2O(l) + NaCl(s) == Na+(aq) + Cl-(aq)

Solubility

• Supersaturated – solution holds more solute than it would at standard conditions

Solubility

Temperature and Solubility• When temperature is increased solubility also

increases• Consider the endothermic reaction below (solid

dissolved in liquid)

KClO3(s) + H2O(l) + heat == K+(aq) + ClO3-(aq)

– Heat acts as a reactant (needs heat to dissolve)

• Adding heat increases solubility makes more solution

Solubility

Solubility

Temperature and Solubility• When temperature is increased solubility

decreases• Consider the exothermic reaction below (liquid

dissolves a gas)

CO2(g) + H2O(l) == Heat + CO2(aq)

– Heat acts as a product (gives off heat)

• Adding heat decreases solubility – What holds more carbonation – warm or cold pop?

Solubility

Pressure and Solubility • Effects of pressure on the solubility of liquids

and solids are minimal.• Effects of pressure on the solubility of gases are

drastic.– Henry’s Law – the solubility of gases increases with

the partial pressure of gases above the solution.• EX: Pop – when you open a can of pop the result is the

carbon dioxide escaping from the solution because the partial pressure of the gases above the pop decreases.

Solubility and Pressure

Solutions

Summary

• Components of a solution

• The dissolving process– Factors affecting dissolving Process

• Solvent Selectivity

• Solubility – Unsaturated / saturated /supersaturated – Temperature / Pressure