Chem 11 2nd Post Lab

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Chem 11 2 nd Post Lab Experiment 6-11 07 April 2015
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Transcript of Chem 11 2nd Post Lab

Chem 11 2nd Post Lab Experiment 5-11

Chem 11 2nd Post LabExperiment 6-1107 April 2015Experiment 6OXYGEN

OxygenImportant for all aerobic organisms. Product of photosynthesis.

Properties at STP: diatomic in nature (O2), colorless, tasteless, highly reactive, soluble in water (DO)

Preparation of OxygenDecomposition of potassium chlorate

Using hydrogen peroxide

Electrolysis of water

Chemical decomposition of water

Combustion of Sulfur with OxygenSulfur burns a bright blue flame when exposed to oxygen.

When the products are exposed to water:

Combustion of Phosphorus with OxygenWhen burned in insufficient oxygen, P4O6 is formed:When burned in sufficient oxygen, P4O10 is formed:

On both cases, a bright yellow orange flame is produced

When exposed to water

Red phosphorusWhite phosphorusOxidation of MetalsCorrosion is the loss of metallic properties of a metal due to oxidation and is accompanied by the formation of unwanted products.

Experiment 8WATERWaterMost abundant compound on the Earths surface, covering 70% of the planet. At room T, it is tasteless, odorless, nearly colorless with a hint of blue. Referred to as the universal solvent.

Purification of WaterSedimentation and Filtration removes insoluble solid impurities (CaCO3)Adsorption def: adhesion of atoms from a gas, liquid, or dissolved solid to a surfaceas a purification technique: it removes disagreeable tastes and odors; specifically, inorganic impurities (NH3) Purification of Water3. Coagulation and Precipitation (flocculation)Primary purpose is to remove turbidity from the water caused by suspended particles.

Al2(SO4)3 + 6H2O 2Al(OH)3(s) + 3H2SO4Purification of Water4. Distillation def: process of separating the component substances from a liquid mixture by selective evaporation and condensation, frees water from salt (NaCl) and other soluble, non- volatile, organic substances

Hard Water vs Soft WaterHard water contains a significant quantity of dissolved minerals such as calcium and magnesium while soft water only has sodium ions.

Temporary Hard WaterTemporary hardness of water is caused by the presence of dissolved bicarbonate minerals (CaCO3). It can be reduced by boiling or through lime softening. Boiling promotes the formation of carbonate from bicarbonate and precipitates calcium carbonate out of the solution.

Permanent Hard WaterIt cannot be removed by boiling; rather, water softeners are used which are ion exchangers. Permanent hardness is caused by the presence of calcium sulfate and/or magnesium sulfate which dont precipitate out as the T increases.Reaction with Soap SolutionTemporary Hard Water2StNa+ + Ca(HCO3)2 CaSt2 + 2NaHCO3

Permanent Hard Water2NaSt + MgSO4 MgSt2 + Na2SO4

Stearate, St C17H35COO- (main and active component of soap)Softening of WaterHow does it work?Principle: ion exchangeWater softeners trade the minerals for something else, in most cases, sodium.

Experiment 9ACIDS, BASES and SALTSTheory of Acids and BasesArrheniusAcid-hydrogen donorBase-Hydroxide ion donorBronsted-LowryAcid- proton donorBase- proton acceptorLewis Acid-electron pair acceptorBase-electron pair donor

Properties of Acids and Bases

Acid and Base Strength

Terms to RememberSalt neutralization product of an acid- base reactionStrong acid HNO3, H2SO4, HCl, HBr, HI, HClO4Concentrated acid an acid solution with high molar concentration of H ionsDibasic or diprotic acid an acid that has 2 H ions to donate to a base in an acid base reaction (H2SO4)Strong base hydroxides of Group 1 and 2 metalsWeak base doesnt fully ionize in an aqueous solutionTriacidic base base with 3 OH per unit (Al(OH)3)Properties of AcidAction on metals:Mg(s) + H2SO4 H2(g) + MgSO4Action on carbonates:Na2CO3 + 2HCl 2NaCl + H2CO3 (test tube)H2CO3 H2O + CO2CO2 + Ca(OH)2 CaCO3 + H2O (watch glass)For carbonates + H2SO4CaCO3 + H2SO4 CaSO4 + H2CO3 (test tube)H2CO3 H2O + CO2 CO2 + Ca(OH)2 CaCO3 + H2O (watch glass)Properties of AcidReactions with carbonates:(a) Na2CO3 + 2HNO3 2NaNO3 + CO2 + H2O(b) 2HNO3 + CaCO3 Ca(NO3)2 + H2O + CO2(c) H2SO4 + Na2CO3 Na2SO4 + H2O + CO2 Conjugate Acid- Base PairsIn order for an acid- base reaction to occur, there must be a transfer of protons between acids and bases. Proton acceptors and proton donors (Bronsted- Lowry) are the basis for these reactions, also referred to as conj. acids and bases.

Sample Problems

Experiment 10Preparation of SaltsSaltsAny ionic compound whose anion comes from an acid and whose cation comes from a base.

Salts Soluble in WaterWhy does water dissolve salt?The polarity of water molecules enables water to dissolve many ionically bonded substances.

Water can dissolve salt because the positive part of water molecules attracts the negative chloride ions and the negative part of water molecules attracts the positive sodium ions.Solubility Tablesolvent: water

Reaction of Aluminum with basesAluminum dissolves in sodium hydroxide with the evolution of hydrogen gas, H2, and the formation of aluminates of the type [Al(OH)4]- which is also salt.

Salts Insoluble in WaterReaction of Pb(NO3)2 with H2SO4: an acid + salt

Reaction of Pb(NO3)2 with K2CrO4: salt + saltPb(NO3)2 + K2CrO4 PbCrO4(s) + 2KNO3

Other methods for salt preparation2Ca + O2 2CaOCaO + H2O Ca(OH)2Ca(OH)2 + CO2 CaCO3 + H2O (breath + lime water)

Sulfur dioxide + limewater chemical rxn:SO2 + 2NaOH H2O + Na2SO3salt: sodium sulfite

Metals are generally reactive, they rarely appear in nature alone; rather, they are typically found with other elements in compound form, often as carbonates and sulfates because they are less soluble in these form than in chlorides, flourides or bromides forms.

Copper Ammonia ComplexCu(NO3)2 + 2NH4OH 2NH4NO3 + Cu(OH)2(s) continued addition of NH4OH results to the formation of a deep blue copper- ammonia complex Complex: a transition metal bonded to ligands (anions with free e- pairs)with excess NH4OH: (precipitate dissolves)Cu(NO3)2 + 4NH4OH(excess) 2NO3 + [Cu(NH3)4]2+

Reaction of Sulfuric Acid with Sodium Hydroxide2NaOH + H2SO4 Na2SO4 + 2H2Osalt formed: sodium sulfate

With excess H2SO4 :NaOH + H2SO4 NaHSO4 + H2Osalt formed: sodium bisulfate


HydrolysisDefined as a reaction involving the breaking of a bond in a molecule using water.

Acid Hydrolysis: increases [H+]

Basic Hydrolysis: increases [OH-]

Rules for Hydrolysis4 possible ways of forming a salt:

HydrolysisCompoundFormed from Acid, Basic or NeutralHydrolysis ReactionNaClSA + SBNeutralNaCl + H2O HCl + NaOHNa2CO3SB + WABasicNa2CO3 + 2H2O H2CO3 + 2NaOHNH4ClWB + SAAcidicNH4Cl + H2O HCl + NH4OHNa2SO4derived from SA NeutralNa2SO4 + 2H2O 2NaOH + H2SO4(NH4)2SO4WB + SAAcidic (NH4)2SO4 + 2H2O 2NH4OH + H2SO4Fe(NO3)3WB + SAAcidicFe(NO3)3 + 3H2O Fe(OH)3 + 3HNO3NaCH3COOSB + WABasicNaCH3COO + H2O NaOH + CH3COOH*bold compounds will dictate the pH of the resulting solutionAmphoterismIn chemistry, an amphoteric species is a molecule or ion that can react as an acid as well as a base.


Amphoterismferric nitrate + sodium hydroxideFe(NO3)3 + 3NaOH 3NaNO3 + Fe(OH)3

zinc nitrate + sodium hydroxideZn(NO3)2 + 2NaOH 2NaNO3 + Zn(OH)2-Zn(OH)2 dissolves in excess NaOHforming a colorless solution

Amphoterismcupric sulfate + sodium hydroxideCuSO4 + 2NaOH Na2SO4 + Cu(OH)2

magnesium nitrate + sodium hydroxideMg(NO3)2 + 2NaOH 2NaNO3 + Mg(OH)2

Amphoterismaluminum nitrate + sodium hydroxideAl(NO3)3 + 3NaOH 3NaNO3 + Al(OH)3 -Al(OH)3 is soluble in excess NaOH forming a colorless solution

Complex- Ion FormationComplex- ion is a product of a Lewis acid- base reaction. Here is an example of a complex- ion formation between copper and ammonia.

Complex- Ion FormationChemical Reactionexcess NH4OH solutionAmmonia complex?(1) Cu(NO3)2 + 3NH4OH Cu(OH)3 + 3NH4NO3blue ppt (+)YES(2) Fe(NO3)3 + 3NH4OH Fe(OH)3 + 3NH4NO3red brown ppt (-)NO(3) Co(NO3)2 + 2NH4OH Co(OH)2 + 2NH4NO3blue ppt (+)YES(4) Cd(NO3)2 + 2NH4OH Cd(OH)2 + 2NH4NO3white ppt (-)NO(5) AgNO3 + NH4OH AgOH + NH4NO3dirty white ppt (+)YES(6) Zn(NO3)2 + 2NH4OH Zn(OH)2 + 2NH4NO3white ppt (-)NO(7) Mg(NO3)2 + 2NH4OH Mg(OH)2 + 2NH4NO3white ppt (-)NO*(+):precipitate dissolves in excess NH4OH*(-):precipitate doesnt dissolves in excess NH4OH

(1)(2)(3)(4)(5)(6)(7)Complex- Ion FormationThe dissolution of the precipitate upon the addition of excess NH4OH would mean a complex formation. Only copper, cobalt and silver formed a complex with ammonia. The chemical reactions are as follow:(1) Cu(OH)2 + 4NH3 [Cu(NH3)4]2+(2) Co(OH)2 + 6NH3 [Co(NH3)6]2+(3) AgOH + 2NH3 [Ag(NH3)2]+

(1)(2)(3)END OF POST LAB 22nd Long EXAM: 10 APRIL 2015