Methods of Separation & Purification Acids, Bases, and Salts C02 & C8.1 – 8.3 Key Notes

Separation & Purification Techniques Filtration – Separating a solid from a liquid –Ex: separating noodles from the pasta water you boiled it in

Crystallization-The formation of a solid from a solution, melted solid, or a vapor. –Example: Dissolving sugar in water then heating to evaporate the water and leave behind sugar crystals.

Distillation-the process of purifying a liquid first by evaporation and then recollecting it through condensation –Example: Desalination of sea water

Fractional Distillation-A special type of distillation where a mixture is separated into its component parts by using differences in their boiling point. –Example: Distillation of Crude Oil –Video Clip

Fractional Distillation of Crude Oil Crude oil when it is mined is thick and sticky (not very useful). The oil is heated in the fractionating column which is hotter at the bottom and cooler at the top. The components with the lowest boiling point turn into vapor first. –Small hydrocarbons (chains of carbon and hydrogen) boil off first and are condensed and collected OR collected as a vapor. –Larger hydrocarbons require higher temperatures and are collected nearer to the bottom of the column.

Chromatography-A technique for separating the components of a mixture on the basis of differences in their attraction to a stationary and a mobile phase. –Example: Separating pigments that make up a dye.

Separation Techniques: Pre-Lab Over next class we will be starting a separation lab in which you will separate a mixture of 4 substances: –Sand –Salt –Iron Filings –Rice grains With your lab partner, begin developing the process you will use to separate this mixture.

Separation Lab Join with your lab partner and as a team: –Create a list of steps that details your plan for separation one step at a time, and describe in words the process you will use to accomplish each step. –Draw a diagram of the setup you will use and create a list of materials to be used. Get your procedure/list checked off before you begin the actual separation.

Acids, Bases, and Salts

Acids and Bases Acids contain H+ ions. –The pH refers to the concentration of H+ present. –Higher H+ concentration = lower pH –pH values BELOW 7 are acidic pH values at 7 are neutral Alkaline solutions, or bases, contain OH- ions. –Higher OH- concentration = higher pH –pH values ABOVE 7 are alkaline

Molecules of acids and alkalis dissociate (break apart into ions) in water. –Eg. HCl (aq)  H + (aq) + Cl - (aq) –Eg. Ammonia gas: NH 3 (aq) + H 2 O (l)  NH 4 + (aq) + OH - (aq) Strong acids and strong alkalis dissociate a lot in water, therefore, have more H+ or OH- ions in solution. –They are good conductors

Testing for acids & bases Use pH paper Use Universal Indicator Use litmus paper.

Types of Substances Nearly any sort of nonmetal oxide forms an acid. –Eg. CO 2, SO 2 in acid rain Some types of non-metal oxides are neutral, like CO (carbon monoxide). They do not react with acids or bases. Nearly any sort of metal oxide and hydroxides form a base or alkali. –Eg. CuO, MgO, Fe 2 O 3 and NaOH –Bases are compounds that react with acid to give only a salt and water. –Alkalis are soluble bases.

Salts In chemistry, scientists describe a salt as a metal compound that can be made from an acid. You will need to know how to make salts. We are doing this in lab, but for more information, check out pg. 158 – 159. Salts are named in the following manner: –Metal first, nonmetal or polyatomic ion second Reacting a metal with HCl gives a chloride salt Neutralization with sulfuric acid gives a sulfate. Neutralization with nitric acid gives a nitrate.

Reactions: Acids + Bases An acid + base will produce a salt and water as part of the neutralization reaction. Neutralization is a reaction with acid that gives water as well as a salt. Acid + Alkali (or base)  Salt + Water –Eg. HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) Hydrochloric acid + sodium hydroxide  sodium chloride + water –Eg. H 2 SO 4 (aq) + CuO (s)  CuSO 4 (aq) + H 2 O (l) Sulfuric acid + copper (II) oxide  copper (II) sulfate + water

Reactions: Acid + Metals An acid + metal will produce a salt and hydrogen gas as part of the displacement reaction. (The metal “displaces” the hydrogen) Acid + Metal  Salt + Hydrogen –Eg. Mg (s) + H 2 SO 4 (aq)  MgSO 4 (aq) + H2 (g) Magnesium + sulfuric acid  Magnesium sulfate + hydrogen

Reactions: Acids + Carbonates An acid + carbonate will produce a salt, water, and carbon dioxide gas as part of a neutralization reaction. Acid + Carbonate  Salt + Water + Carbon Dioxide –Eg. CaCO 3 (s) + 2HCl (aq)  CaCl 2 (aq) + H2O (l) + CO 2 (g) Calcium carbonate + hydrochloric acid  calcium chloride + water + carbon dioxide

Be Careful! Ammonium vs. Ammonia NH 4 + NH 3

Acidity in the Environment Acids and alkalis are corrosive. They can burn through substances (including skin) and cause great harm if not handled carefully. Why do you think it is important to control acidity in: –The air –The water –The soil