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

http://www.ssc.education.ed.ac.uk/bsl/chemistry/filtrationd.html

• 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.

http://scienceisfun.wiki.hci.edu.sg/Separation+Techniques

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

water

http://www.gcsescience.com/e7-fractional-distillation.htm

• 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

http://en.wikipedia.org/wiki/Fractional_distillation

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.

http://socratic.org/questions/how-does-solubility-affect-chromatography

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:

NH3 (aq) + H2O (l) NH4+ (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. CO2 , SO2 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, Fe2O3 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) + H2O (l)• Hydrochloric acid + sodium hydroxide

sodium chloride + water

– Eg. H2SO4 (aq) + CuO (s) CuSO4 (aq) + H2O (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) + H2SO4 (aq) MgSO4 (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. CaCO3 (s) + 2HCl (aq) CaCl2 (aq) + H2O (l) + CO2 (g)• Calcium carbonate + hydrochloric acid calcium

chloride + water + carbon dioxide

Be Careful!

• Ammonium vs. Ammonia• NH4

+ NH3

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