Presentation on theme: "Reactions in Aqueous Solutions"— Presentation transcript:
1 Reactions in Aqueous Solutions General properties of aqueous solutionsPrecipitation ReactionsAcid-Base ReactionsOxidation-Reduction ReactionsConcentration of SolutionsGravimetric AnalysisAcid-Base TitrationsRedox Titrations
2 General Properties of Aqueous Solutions: definitions Solution: a homogeneous mixture of two or more substancesSolute: the substance present in a smaller amountSolvent: the substance present in a larger amountAqueous Solution: the solute is initially a solid or a liquid and the solvent is water
3 Electrolytic Properties Electrolyte: a substance whose dissolution in water results in a solution that conducts electricityNon-electrolyte: a substance whose dissolution in water results in a solution that does not conduct electricityDissociation: when the compound is broken down into cations and anionsHydration: when an ion is surrounded by water in a particular wayIonization: when acids and bases separate into ionsReversible Reaction: when a reaction can occur in both directionsChemical equilibrium: when no net change in a reaction can be observedExamples of Electrolytes and Non-electrolytesStrong electrolytes: HCl, NaOH, and ionic compoundsWeak electrolytes: water (very weak), HFNon-electrolytes: methanol, glucose and urea
4 Precipitation Reactions A precipitate: the insoluble solid that forms from a reactionPrecipitate reactions form precipitatesSolubility: the maximum amount of solute that can dissolve in a given amount of solvent and a specific temperatureInsoluble compounds: carbonates, phosphates, chromates, sulfides (not when with compounds with alkali metal ions and ammonium ion)Soluble compounds: compounds with alkali metal ions,ammonium ion, nitrates, bicarbonates, chlorates, halides (not with silver, mercury or lead) and sulfates (not with silver, calcium, strontonium, barium, mercury or lead)Other insoluble compounds: hydroxides, except when with compounds with alkali metal ions and barium ion
5 Molecular, Ionic and Net Ionic Equations Molecular equations: the formulas are written as if all species existed as molecules or whole unitsExample: NaCl (aq) + AgNO (aq) AgCl (s) + NaNO (aq)Ionic equations: all the dissolved species are expressed as free ionsExample: Na (aq) + Cl (aq) + Ag (aq) + NO (aq) AgCl (s) + Na (aq) + NO (aq)Net ionic equations: only the undissolved species are expressed on both sides of the reactionExample: Ag (aq) + Cl (aq) AgCl (s)
6 Acids and Bases Properties of Acids Sour taste Color change of litmus paper blue to redReacts with some metals to produce hydrogen gas and with carbonates and bicarbonates to produce carbon dioxideAqueous acidic solutions conduct electricityBronsted Acid: proton donorProperties of BasesBitter tasteSlippery feelColor change of litmus paper red to blueAqueous basic solutions conduct electricityBronsted Base: proton acceptor
7 Acid-Base Neutralization A reaction between a base and an acid is called a neutralization reaction.The most common occurrence of this is when and acid and base yield water and a salt.In an example we can use the most widely laboratory used acid and base: hydrochloric acid and sodium hydroxide. This reaction yields water and table salt (sodium chloride).HCl +NaOH NaCl + water
8 Oxidation-Reduction Reactions Electron-transfer reactions are known as oxidation-reduction reactions or redox reactionsEach step is called a half-reaction where the loss/gain of electrons is clearly shownAn oxidizing agent is one that accepts electrons and the reducing agent is one that donates electrons
9 Oxidation numbers (or states) Oxidation numbers or oxidation states are the number of charges the atom would have in a molecule, or an ionic compound, if electrons were transferred completelyRules of oxidation numbers:free elements, or uncombined elements, always have an oxidation state of zero-monoatomic ions have an oxidation state equal to that of their charge-for the most part oxygen has an oxidation state of -2, except for in hydrogen peroxide and peroxide where the oxidation state is -1-usually the oxidation number of hydrogen is +1, except for when with binary compounds where it is -1-the oxidation state of fluorine is always -1, for chlorine bromine and iodine the state is negative when as halide ions but positive when with oxygen-polyatomic ions must have charges that add up to the net charge-lastly, oxidation numbers do not have to be integers
10 Combination reactions are generally represented by A + B C, in this type of reaction, two or more substances combine to form one product. Decomposition reactions are generally represented by C A+B, here one substance decomposes into at least two simpler substances.
11 Displacement reactions There are three different types of displacement reactions: hydrogen displacement, metal displacement and halogen displacementIn a hydrogen displacement reaction hydrogen is yielded as one of the productsmetal is yielded in a metal displacement reactiona halogen, such as fluorine, chlorine, bromine or iodine, is produced in a halogen displacement reaction
12 Disportionation reactions Disportionation reactions have a unique quality, which is that an element is both oxidized and reduced.In order for this to happen the element must have at least three oxidation states, one such element is oxygen.When hydrogen peroxide is decomposed into water and oxygen three different oxidation numbers exist for oxygen in the reaction. When oxygen is part of hydrogen peroxide, its oxidation number is -1, in water its oxidation number is -2 and by itself as a free element its oxidation state is 0.
13 Concentration of a solution The concentration of a solution depends on how much solute is present in a specific amount of solvent or solution.For this section we will focus on one expression of concentration which is molarity (M), or molar concentration.This is determined by how many moles of solute are in how many liters of solution M = mol / L
14 Obtaining desired molarity We would multiply the desired molarity by the desired final volume to get the necessary number of moles.Then we would have to convert moles to grams.Using the final number of grams necessary we would place it all in a flask large enough to hold and measure the desired final volumeby adding water until we reach that final volume we would attain our desired molarity.
15 Dilutiondilution of a solution is making a concentrated solution less concentrated.In order to do this we must realize that there is 1 mole of solute in 1 liter of solution.We take a portion of the concentrated solution and dilute it enough to make the desired molarity.Initial molarity multiplied by initial volume is equal to final molarity multiplied by final volume
16 Gravimetric AnalysisGravimetric Analysis is a very accurate technique of measuring the amount of substance in a sample by measuring the mass of the formed precipitate, as long as the entire reaction is totally completed.The precipitate also needs to be completely insoluble, otherwise part of the precipitate would not be solid, but aqueous and would have filtered through.
17 Acid-Base TitrationsDuring a titration a standard solution (a solution of accurately known concentration) is added gradually to another solution of unknown concentration, until the chemical reaction between the two solutions is complete.Through titration we can find the exact concentration of the original solution of unknown concentration by calculations as long as we know the original volumes.In acid-base titrations we must use indicators to let us know when the equivalence point has been reached, or in other words the titration is complete and the acid has been thus completely neutralized by the base.
18 Redox TitrationsOxidation-Reduction titrations are very similar to acid-base titrations, only an equivalence point is reached when the reducing agent is completely oxidized.Again a good indicator is necessary, and sometimes the oxidizing agent can act as an indicator because it changes color drastically when it is oxidized versus reduced.