Lecture Presentation Ashley Warren Kings High School AP Chemistry

Name: Lecture Presentation Ashley Warren Kings High School AP Chemistry
Uploaded: 2017-08-15T17:46:53+00:00
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Description: Lecture Presentation Ashley Warren Kings High School AP Chemistry

Lecture Presentation Ashley Warren Kings High School AP Chemistry
Water covers nearly two-thirds of our planet, and the chemical reactions in which water is the dissolving medium are imperative! LO 3.2, 2.9, 1.4, **1.19 and (gravimmetric and volumetric analysis) Example: mL of Pb(NO3) 2 solution with an unknown concentration reacts with excess aqueous Rb3 AsO4. After filtering and drying, g of precipitate is found. What is the concentration of the lead(II) nitrate solution? M(Pb3(AsO4) 2) = g/mol Measure the concentration of solution by measuring the volume of solution need to find stoichiometric equivalence between reactants using a titration. - Use volume of titrant to find moles of analyte. - Divide moles of analyte by volume of analyte to find concentration. - Acid/base reactions are commonly used but not always. Example: What is the concentration of an HBr solution when mL is titrated with mL of M KOH? FRQ: Tisko Aqueous Solns…..great one. Ashley Warren Kings High School AP Chemistry © 2012 Pearson Education, Inc.

© 2012 Pearson Education, Inc.
Solutions An aqueous solution is a solution in which water is the dissolving medium. Solutions are defined as homogeneous mixtures of two or more pure substances. The solvent is present in greatest abundance. All other substances are solutes. Remember that solutes are said to be dissolved in the solvent. © 2012 Pearson Education, Inc.

Dissociation An electrolyte is a substances that dissociates into ions when dissolved in water. A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so. © 2012 Pearson Education, Inc.

Electrolytes In order for the bulb to light up, there must be a current (flow of electrically charged particles) between the two electrodes immersed in the solution. In sodium chloride solution, the sodium chloride crystal dissociates into ions, these ions carry the electrical charge from one electrode to the other which completes the circuit. When sucrose dissolves it does not create ions…instead there are neutral sucrose molecules surrounded by water molecules. A strong electrolyte dissociates completely when dissolved in water. A weak electrolyte only dissociates partially when dissolved in water. © 2012 Pearson Education, Inc.

Chemical Equilbrium HCl (aq)  H+ (aq) + Cl- (aq) CH3COOH (aq) = CH3COO- (aq) + H+ (aq) What is the biggest difference between the two reactions above? Which represents a strong electrolyte and which represents a weak? Why? Acetic acid (the second reaction) will not break down completely into ions like hydrochloric acid does. In the first equation we see that HCl breaks down completely…we know this because of the single arrow. This represents that the reaction taking place is completely breaking down into the products with no room for reactants left over. The second equation is different. Instead, we show this reaction happening with half arrows indicating that some of the acetic acid is forming ions, but also at the same time some of these ions are recombining to form acetic acid again. This balance produces a state of chemical equilibrium. This means the relative numbers of each type of ion or molecule in the reaction are constant over time. © 2012 Pearson Education, Inc.

Dissociation When an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and solvates them. This process is called dissociation. When NaCl dissolves in water, each ion separates from the solid structure and disperses throughout the solution. Remember that water molecules will separate, surround, and uniformly disperse the ions into the liquid. © 2012 Pearson Education, Inc.

Solvation Solvation helps stabilize the ions in the solution and prevents cations and anions from recombining. Why does water help do this? Since ions are free to move, they become dispersed uniformly. Water is a very effective solvent fro ionic compounds. Although it is electrically neutral as a molecules, the oxygen atom is rich in electrons (very electronegative) and has a partial negative charge. Each hydrogen atom has a partial positive charge (very electropositive). Cations are attracted by the oxygen end and anions are attracted by the positive ends. © 2012 Pearson Education, Inc.

Electrolytes and Nonelectrolytes
Soluble ionic compounds tend to be electrolytes. Why? Molecular compounds tend to be nonelectrolytes, except for acids and bases. As an ionic compound dissolves, we are left with ions able to carry an electric charge. These ions are surrounded by water molecules and they are said to be solvated. When a molecular compound dissolves in water, the solution usually consists of intact molecules dispersed throughout the solution. Consequently, most molecular compounds are nonelectrolytes bc there are no charges to interact with the water molecules. A few molecular substances have aqueous solutions that contain ions. Acids are the most important of these. © 2012 Pearson Education, Inc.

Strong Electrolytes Are…
Strong acids Strong bases © 2012 Pearson Education, Inc.

Precipitation Reactions
Reactions that result in the formation of an insoluble product are called precipitation reactions Precipitates are insoluble solids formed by a reaction in solution. We know if ppts. form bc we can predict them by the solubility guidelines. Precipitation reactions occur when pairs of oppositely charged ions attract each other so strongly that they form an insoluble ionic solid. The solubility of a substance at a given temperature is the amount of the substance that can be dissolved in a given quantity of solvent at the given temperature. Any substance Pb(NO3)2 (aq) + 2 KI (aq)  PbI2 (s) + 2KNO3 (aq) © 2012 Pearson Education, Inc.

Solubility In the insoluble cases…the attraction between the oppositely charged ions in the solid is too great for the water molecules to separate the ions to any significant extent so the substance remains largely undissolved. Experimental observations have led us to these solubility rules. These rules are designated by anions…but note one big hint! All common ionic compounds of the alkali metal ions and ammonium ion are soluble in water. The solubility of a substance at a given temperature is the amount of the substance that can be dissolved in a given quantity of solvent at the given temperature. Any substance with a solubility less than 0.01 mol/L will be referred to as insoluble.

Metathesis (Exchange) Reactions
Metathesis comes from a Greek word that means “to transpose.” It appears as though the ions in the reactant compounds exchange, or transpose, ions. Reactions in which cations and anions appear to exchange partners conform to the general equation: AX + BY  AY + BX AgNO3(aq) + KCl(aq)  © 2012 Pearson Education, Inc.

Metathesis Reactions Steps to complete and balance these reactions: Use the chemical formulas to determine which ions are present. Write the chemical formulas of the products by combining the cation from one reactant with the anion of the other, using ionic charges to determine the correct subscripts. Check the solubilities of the products. Balance. Remember for a ppt reaction to occur…one of the products must be insoluble. If both products are soluble, then the reaction does not happen. © 2012 Pearson Education, Inc.

Solution Chemistry It is helpful to pay attention to exactly what species are present in a reaction mixture (i.e., solid, liquid, gas, aqueous solution). If we are to understand reactivity, we must be aware of just what is changing during the course of a reaction. © 2012 Pearson Education, Inc.

Molecular Equation The molecular equation lists the reactants and products in their molecular form: AgNO3(aq) + KCl(aq)  AgCl(s) + KNO3(aq) This equation shows the complete chemical formulas of the reactants and products. © 2012 Pearson Education, Inc.

Complete Ionic Equation
In the complete ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions. This more accurately reflects the species that are found in the reaction mixture: Ag+(aq) + NO3−(aq) + K+(aq) + Cl−(aq)  AgCl(s) + K+(aq) + NO3−(aq) Remember that we cannot dissociate anything that is a liquid, solid, or gas….only aqueous solutions dissociate into ions. © 2012 Pearson Education, Inc.

Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right: Ag+(aq) + NO3−(aq) + K+(aq) + Cl−(aq)  AgCl(s) + K+(aq) + NO3−(aq) What is the name of the ions that we cross out on both sides of the equation? And why do we cross them out? Spectator Ions – they play no direct role in the reaction! © 2012 Pearson Education, Inc.

Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. The only things left in the equation are those things that change (i.e., react) during the course of the reaction: Ag+(aq) + Cl−(aq)  AgCl(s) This is your net ionic equation. The equation that shows only the ions and molecules directly involved in the reaction. © 2012 Pearson Education, Inc.

Writing Net Ionic Equations
Write a balanced molecular equation. Dissociate all strong electrolytes. Cross out anything that remains unchanged from the left side to the right side of the equation. Write the net ionic equation with the species that remain. © 2012 Pearson Education, Inc.

Acids The Swedish physicist and chemist S. A. Arrhenius defined acids as substances that increase the concentration of H+ when dissolved in water. Both the Danish chemist J. N. Brønsted and the British chemist T. M. Lowry defined them as proton donors. Lewis defined them as electron acceptors. Acids ionize in aq solutions to form hydrogen ions. Remember that the Hydrogen ion is simply a proton which is why we can call it a proton transfer. Protons in aq solutions are solvated by water molecules. We thus write H+ as H+ (aq) © 2012 Pearson Education, Inc.

Acids Molecules of different acids ionize to form different numbers of H+ ions. Monoprotic Acids (yield one H+ ion per acid) Diprotic Acids (yields 2 H+ ions per acid) Polyprotic Acids ionize in steps H2SO4 (aq)  H+ (aq) + HSO4- (aq) HSO4- (aq)  H+ (aq) + SO42- (aq) Only the first ionization is complete. The second equation should be a double arrow. © 2012 Pearson Education, Inc.

Bases Arrhenius defined bases as substances that increase the concentration of OH− when dissolved in water. Brønsted and Lowry defined them as proton acceptors. Lewis defined them as electron donors. Bases release OH- ions into solution. Bases accept Hydrogen ions. Remember that bases do not just have to contain hydroxide. Ammonia is also considered a basic compound. When added to water it accepts a hydrogen ion to produce hydroxide ion and ammonium ion. © 2012 Pearson Education, Inc.

Reactivity of Strong and Weak Acids/Bases
When reactivity depends only on H+ (aq) concentrations, strong acids are more reactive than weak acids. The reactivity of an acid, however, can depend on the anion concentration. HF is a weak acid, but it is very reactive and attacks many substances. © 2012 Pearson Education, Inc.

Comparing Acid Strengths
The following represent aqueous solutions of acids HX, HY, and Hz, with water molecules omitted. Rank the acids from strongest to weakest. © 2012 Pearson Education, Inc.

Identifying Strong/Weak Electrolytes
Classify the following as strong, weak, or nonelectrolyte: CaCl2, HNO3, C2H5OH (ethanol), HCOOH (formic acid), KOH Rank the following compounds that are dissolved in water in order of increasing electrical conductivity: Ca(NO3)2, C6H12O6, NaCH3COO, CH3COOH © 2012 Pearson Education, Inc.

Neutralization Reactions
Generally, when solutions of an acid and a metal hydroxide base are combined, the products are a salt and water: CH3COOH(aq) + NaOH(aq) NaCH3COO(aq) + H2O(l) © 2012 Pearson Education, Inc.

When a strong acid reacts with a strong base, the net ionic equation is HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) H+(aq) + Cl−(aq) + Na+(aq) + OH−(aq)  Na+(aq) + Cl−(aq) + H2O(l) © 2012 Pearson Education, Inc.

When a strong acid reacts with a strong base, the net ionic equation is HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) H+(aq) + Cl−(aq) + Na+(aq) + OH−(aq)  Na+(aq) + Cl−(aq) + H2O(l) H+(aq) + OH−(aq)  H2O(l) © 2012 Pearson Education, Inc.

Gas-Forming Reactions
Some metathesis reactions do not give the product expected. In this reaction, the expected product (H2CO3) decomposes to give a gaseous product (CO2): Many bases besides hydroxide react with hydrogen ion to form molecular compounds. Two if these are the sulfide ion and the carbonate ion. Both of these ions react with acids to form gases that have low solubilities in water. CaCO3(s) + HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) © 2012 Pearson Education, Inc.

When a carbonate or bicarbonate reacts with an acid, the products are a salt, carbon dioxide, and water: CaCO3(s) + HCl(aq) CaCl2(aq) + CO2(g) + H2O(l) NaHCO3(aq) + HBr(aq) NaBr(aq) + CO2(g) + H2O(l) Write the net ionic equations for these!!! © 2012 Pearson Education, Inc.

This reaction gives the predicted product, but you had better carry it out in the hood, or you will be very unpopular! But just as in the previous examples, a gas is formed as a product of this reaction: H2S gives rotten eggs their foul odor. Write net ionic equation! Na2S(aq) + H2SO4(aq)  Na2SO4(aq) + H2S(g) © 2012 Pearson Education, Inc.

Oxidation-Reduction Reactions
Let’s recap…in ppt rxns, cations and anions come together to form an insoluble ionic compound. In neutralization rxns, H+ and OH- ions come together to form water molecules. Now, we have a third kind of reaction: redox! In a redox reaction, electrons are transferred from one reactant to another. As of now we are going to focus on one of the reactants as a metal in its elemental form. Most common example of redox rxn would be corrosion! When a metal corrodes, each metal atom loses electrons and so forms a cation, which can combine with an anion to form an ionic compound. Remember that in oxidation, the atom becomes more positively charged. In reduction the atom becomes more negatively charged. Why do we call it oxidation? The first studied rxns of this kind dealt with oxygen. Many reactions occur with oxygen in the air to form metal oxides….the metal loses electrons to oxygen Imperative to remember that in every oxidation reduction reaction, the oxidation numbers of at least 2 atoms must change. 2Ca (s) + O2 (g)  2CaO (s) An oxidation occurs when an atom or ion loses electrons. A reduction occurs when an atom or ion gains electrons. One cannot occur without the other. © 2012 Pearson Education, Inc.

Oxidation Numbers To determine if an oxidation–reduction reaction has occurred, we assign an oxidation number (or you may hear oxidation state) to each element in a neutral compound or charged entity. Of course there are rules!  © 2012 Pearson Education, Inc.

Oxidation Numbers The Rules
Elements in their elemental form have an oxidation number of 0. This includes diatomics The oxidation number of a monatomic ion is the same as its charge. Alkali metals always have +1 Alkaline earth metals always have +2 Aluminum is always +3 © 2012 Pearson Education, Inc.

Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. Oxygen has an oxidation number of −2, except in the peroxide ion, in which it has an oxidation number of −1. Hydrogen is −1 when bonded to a metal, but it is usually +1 because it’s typically bonded to a nonmetal. © 2012 Pearson Education, Inc.

Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. Fluorine always has an oxidation number of −1. The other halogens have an oxidation number of −1 when they are negative; they can have positive oxidation numbers, however, most notably in oxyanions. © 2012 Pearson Education, Inc.

Displacement Reactions
In displacement reactions, ions oxidize an element. The ions, then, are reduced. The reaction between a metal and either an acid or a metal salt conforms to the general pattern: A + BX  AX + B These are called displacement reactions because the ion in solution is displaced (replaced) through oxidation of an element. © 2012 Pearson Education, Inc.

Activity Series We use the activity series to predict whether a certain metal will be oxidized either by an acid or by a particular salt. Different metals vary in the ease with which they are oxidized. Zn is oxidized by aqueous solutions of copper, but silver is not. Zinc therefore loses electrons more readily than silver….that is zinc is easier to oxidize than silver. The activity series is a list of metals arranged in order of decreasing ease of oxidation. The metals at the top of the table, like alkali metals and alkaline earth metals are most easily oxidized….that is they react most readily to form compounds. They are called the active metals The metals at the bottom like the transition metals are very stable and form compounds less readily. These are called noble metals. Any metal on the list can be oxidized by the ions of elements below it. For example, copper is above silver in the series…thus copper metal is oxidized by silver ions. Remember that only metals above hydrogen are able to react with acids to form H2. © 2012 Pearson Education, Inc.

Analyzing Chemical Reactions for Patterns
Imperative to recognize/identify patterns in reactions so that you gain a chemical intuition. Helpful questions can help you determine the reaction: What are the reactants? Are they electrolytes or nonelectrolytes? Are they acids and bases? Will metathesis produce a ppt? Water? Gas? Do reactants engage in redox? © 2012 Pearson Education, Inc.

Molarity Two solutions can contain the same compounds but be quite different because the proportions of those compounds are different. Molarity is one way to measure the concentration of a solution: moles of solute volume of solution in liters Molarity (M) = Scientists use the term concentration to designate the amount of solute dissolved in a given quantity of solvent or quantity of solution. Remember: The greater the amount of solute dissolved in a certain amount of solvent, the more concentrated the resulting solution. © 2012 Pearson Education, Inc.

Mixing a Solution To create a solution of a known molarity, one weighs out a known mass (and, therefore, number of moles) of the solute. The solute is added to a volumetric flask, and solvent is added to the line on the neck of the flask. © 2012 Pearson Education, Inc.

Dilution One can also dilute a more concentrated solution by Using a pipet to deliver a volume of the solution to a new volumetric flask, and Adding solvent to the line on the neck of the new flask. © 2012 Pearson Education, Inc.

Dilution The molarity of the new solution can be determined from the equation Mc  Vc = Md  Vd, where Mc and Md are the molarity of the concentrated and dilute solutions, respectively, and Vc and Vd are the volumes of the two solutions. © 2012 Pearson Education, Inc.

Titration To determine the concentration of a particular solute in a solution, chemists often use titration…which involves combining a solution where the solute concentration is not known with a reagent solution of known concentration called a standard solution. Just enough standard solution is added to completely react with the solute in the solution of unknown concentration. The point at which stoichiometrically equivalent quantities are brought together is known as the equivalence point. Titration is an analytical technique in which one can calculate the concentration of a solute in a solution. © 2012 Pearson Education, Inc.

Titration Ag+ (aq) + Cl- (aq)  AgCl (s) How many grams of chloride ion are in a sample of the water if 20.2 mL of M Ag+ is needed to react with all the chloride in the sample? If the sample has a mass of 10.0 g, what percent Cl- does it contain? © 2012 Pearson Education, Inc.

Lecture Presentation Ashley Warren Kings High School AP Chemistry

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