Lecture 4 Classification of Mixtures Solutions Solubility Water Treatment

Mixtures Mixture: a combination of two or more substances in which each substance retains its own properties. –Most materials are mixtures.

CompoundElementMixture

The formation of a mixture is considered a physical change. –No new substance is formed – mixtures do not form from chemically bonded atoms. –Each substance retains its chemical identity. –Can be separated by physical means.

Separating Mixtures Filtration: use of a filter in the separation of a solid- liquid mixture. –Commonly part of the water- purification process.

Separating Mixtures Distillation: –Takes advantage of differences in boiling or melting points (ex. water boils at 100°C, salt melts at 800°C). –Heat seawater to 100°C and water becomes a vapor while salt is left behind. –Water vapor is collected, cooled, and condensed into pure liquid water.

Classification of Matter Pure: consists of only a single element or a single compound. Impure: a mixture containing 2 or more elements and compounds.

Classification of Matter Heterogeneous Mixture: different components of mixture are distinguishable.

Classification of Matter Homogeneous Mixture: mixture with the same composition throughout – individual components are not visible.

Classification of Matter Solution: a homogeneous mixture in which all components are in the same phase. –Examples: salt water, metal alloys, air Suspension: a homogeneous mixture in which the different components are in different phases. –Examples: milk, fog, blood

Ruby = a solid solution of aluminum oxide and red chromium compounds. Solutions can be solids, liquids, or gases.

The path of light made visible by a suspension.

Solutions Solvent: (dissolves other materials) component of a solution present in the greatest quantity. –Example: water Solute: (gets dissolved) present in lesser amounts. –Example: salt

Saturated Solution: a solution in which no more solute can be dissolved. Unsaturated Solution: a solution that has not reached the limit of solute that can be dissolved.

Solutions Concentration: the amount of solute dissolved per amount of solution. = amount of solute / amount solution Example: a solution of sugar-water has 2g of sucrose per liter of solution.

Solubility Solubility: the ability of a solute to dissolve in a solvent. Solubility depends on: –electrical attractions between solute and solvent particles. –attraction of solute particles for one another. –attraction of solvent particles for one another.

Sucrose molecules held together by multiple strong hydrogen bonds. Multiple H 2 O molecules needed to pull sucrose molecules away from one another. Places a limit on how much sucrose can be dissolved.

Solubility Infinitely soluble: –When attractions between solute molecules are similar to attractions between solvent molecules. –Examples: water and ethanol, gases in atmosphere.

Infinitely soluble: Can be mixed in any proportions.

O 2 and Water: –Only g of O 2 can dissolve in 100 mL of water. –Relatively weak attractions between O 2 (nonpolar) and H 2 O (polar). –Water molecules have stronger attractions for one another.

Solubility Insoluble: a material that does not dissolve in a specific solvent. –Example: sand and glass are insoluble in water. –However, sand and glass are soluble in HF acid.

Solubility Solubility changes with temperature. Many water-soluble solids dissolve more easily in hot water than in cold water. –Water molecules move more rapidly. –More violent collisions with solute molecules. –Collisions disrupt bonds between solute molecules.

Some water-soluble solids become less soluble as water temperature increases. –Calcium Carbonate (CaCO 3 ) precipitates out of solution as a solid at higher temperatures.

Solubility Precipitate: solid residue formed when the solubility of a solid substance decreases in a solution. Caused by changes in: –temperature. –concentration.

Solubility The solubility of gases in liquids decreases with increasing temperature. –gas molecules are ejected by the increasingly energetic solvent molecules. –Example: carbonated beverages go flat faster when warm.

Solubility Solubility of a gas also depends on the pressure of the gas above the liquid. –Higher pressures allow for more gas to be dissolved - more gases forced into solution.

Solubility When a gas solute comes out of solution it forms bubbles – “fizzing”. Gas molecules collect together forming bubbles that rise to the surface due to lower density.

Water Purification One of the most important global issues is the supply of clean freshwater for a growing population and economy.One of the most important global issues is the supply of clean freshwater for a growing population and economy.

Water Purification Removal of solids (dirt, bacteria) in suspension.

Water Purification Filter water through sand and gravel. Odor and flavor improved by aerating the water – some air dissolved into water.

Water Purification Disinfected with Cl 2 or sometimes O 3. Many diseases are contracted by drinking contaminated water. –Example: in the early 1990’s, when the Peru government stopped the chlorination of its water supply, there were 1.3 million new cases of cholera and 13,000 deaths.

Disinfection by exposure to UV radiation.

Disinfection of water by exposure to solar UV radiation.

Desalination Greatest water reserves contain seawater and brackish (moderately salty) water. Two processes for removing salts: –Distillation –Reverse Osmosis Also important methods for removing contaminants such as fertilizers and pesticides.

Desalination Distillation:Distillation: –Very energy-intensive because of water’s high heat of vaporization and high heat capacity. –Many distillation plants require the burning of large quantities of fossil fuels.

Desalination Solar Distillers: require about 1 m 2 surface area to produce 4 L of fresh water per day.

Desalination Osmosis: the net flow of water across a semi-permeable membrane into a more concentrated solution.

Reverse Osmosis: water is forced across a semipermeable membrane into a less concentrate solution.

Modern reverse osmosis facilities can produce millions of gallons of freshwater per day.