Chemistry Unit 4 (11)

* What does matter consist of? 

* Pure substances and mixtures 

* Pure substances consist of: 

* Elements and Compounds, both are uniform in appearance 

* Mixtures are: 

* Homogeneous and heterogeneous 

* Heterogenous: 

* components are visible 

* Homogenous: 

* Uniform in appearance 

* Solutions are: 

* Homogeneous (one phase) 
* Contain more than 1 type of particle 
* clear/ coloured
* Can be solid, liquid and gas 

* Solutions contain: 

* Solute and solvent, both can act vice versa in miscible liquid 

* Solute: 

* Substance that is dissolved 

* Solvent: 

* Substance in which solute is dissolved, like water for aqueous solutions 

* Variable compositions: 

* Different solutions have various ratios of solute and solvent 

* Miscible liquid: 

* Liquid that can be combined in any proportion; both liquids can be the solute/ solvent 

* Immiscible liquid: 

* Liquids that do not dissolve one another; neither act as solute or solvent (oil & water)

* What is solubility and how is it found: 

* Maximum amount that a a solute dissolves in a solvent at a particular temperature, measured in g/100mL
* a polarity dependent
* Found by dissolving solute in solvent until it no longer dissolves 
* Or merck index 

Unsaturated solution:

* more solute dissolves 

Saturated solution:

* no more solute can dissolve (max) 

Supersaturated solution:

* more than maximum solute, unstable, crystals form

Why do ionic compounds dissolve in water? 

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* Intermolecular forces b/t molecules

Water’s intermolecular force

* b/t opposite charges on 2 different polar molecules 
* Spl dipole-dipole force seen in water, hydrogen bonding
* Thus every water molecule can form 4 hydrogen bonds to other water molecules 

How ionic compounds dissolve in water

* Crystal (ionic compound) is placed in water 
* Water molecules immediately surround the ions on the surface of the crystal (ion-dipole) 
* The positive H atoms on some water molecules become attracted to negatively charged chloride ions 
*  the - O atoms on other water molecules become attracted to the positive charged sodium ions 
* The electrostatic attractive forces b/t the water molecules and the individual ions is greater than the attractions b/t the ions in the crystal 
* The water molecules pull these ions away from the crystal lattice into the solution

* What do ionic compounds do in water? 

* very soluble
* molecules dissociate/ separate into aqueous ions 
* They become solvated 

* Solvated: 

* Process by which ions are attracted to and surrounded by solvent molecules 
* State is (aq) 


* Aka Hydrated, if the solvent is water 
* Hydrated ions conduct electricity, the solution is called electrolytes 

Electrolytes:

*  the solution in which hydrated ions conduct electricity

* Like dissolves like, so… 

* Polar dissolves polar 
* Non-polar dissolves non-polar

* Solubility and covalent compounds: 

* Many covalent compounds do not have +/- charges, so they are not soluble in water, but there are exceptions that dissolve because of their polar bonds : 
* Methanol 
* Ethanol 
* Sucrose 
* Still these exceptions do not conduct electricity, they are non-electrolytes 

non electrolytes _____ conduct electricity

do not

* Ethanol: 

* Non-polar and polar bonds 
* C-H bonds = non-polar bonds very little difference in electronegativity 
* Like water O-H = polar bond 

Hydrogen bonding

*  partially positive hydrogen atom of one molecule is attracted to the partially negative oxygen of a neighbouring molecule 

as the non-polar part increases in size, the solubility _______, because….

decreases…. Most polar and ionic compounds will mix with water

A molecule of ethanol is soluble in water, process:

* Can form h bonds and dipole-dipole bonds w/ water, so it is soluble in water 
* Increased length of carbon “chain” decreases solubility in water (as the number of carbon atoms increases, the solubility of the compound in water decreases) 
* It has a dipole so it can form a dipole-dipole force w/ water 

* Factors that affect the rate of dissolving

* Temperature 
* Rate of dissolving is greater at higher temperatures
* = greater KE 
* = more movement 
* = more collisions w/ solute particles 
* Agitation 
* Mixing, stirring, shaking container increases rate of dissolving as it brings fresh solvent into contact with undissolved solid 
* Particle size 
* Decreasing the size of particles increase the rate of dissolving 
* Small pieces of solute
*  = more surface area than 1 large piece
* = more contact b/t solvent and solute

Rate of dissolving:

how quick a solute dissolves in a solvent

* Factors that affect solubility 

* Temperature 
* Solids 
* Increases solubility of most solids by providing it w/the energy needed to break bonds between particles 
* Liquids 
* Does not affect the solubility of liquids as they have the needed energy
* Gases 
* Decreases the solubility of gases because they alr have a lot of energy 
* They must lose energy to dissolve into a liquid 
* More energy causes them to come out of a sol’n
* Pressure 
* Only affects the solubility of gases 
* Liquids and solids are virtually incompressible 
* High pressure pushes gas molecules close together and makes them more likely to interact with a liquid solvent 
* High pressure = more gas molecules are soluble
* Particle size 
* Small molecules are more soluble than larger molecules b/c greater amt of SA and contact b/t solute and solvent

Concentration:

* measure of the amount of solute particles to solvent in a solution

Concentrated solution

*  a high number of solute particles in the solvent

Dilute solution

* small number of particles in the solvent

Molar concentration

* Aka molarity 
* Number of moles of solute dissolved in one litre of sol’n 
* In mol/L or M