Chapter 4 Reactions in Aqueous Solutions PDF

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Chapter 4 Reactions in Aqueous Solutions 1. General Properties of Aqueous solutions 1. Solution: a homogenous mixture of two or more substances 1. May be gaseous, solid, or liquid 2. Solute: the dissolved substance in a solution 3. Solvent: a substance present in the largest amount 2. Electrolytes and Nonelectrolytes 1. Every water soluble substance fits into one of these two categories 1. Electrolyte: a substance that dissolves in water to yield a solution the conducts electricity 2. Nonelectrolyte: a substance that dissolves in water to yield a solution that does not conduct electricity 2. The difference between an aqueous solution that conducts electricity and one that does not is the presence or absence of ions 1. Dissociation: the process by which an ionic compound, upon dissolution, breaks apart into its constituent ions; the presence of ions is what allows the solution to conduct electricity 2. Ionization: the process by which a molecular compound forms ions when it dissolves 3. Strong Electrolytes and Weak Electrolytes 1. Strong electrolyte: an electrolyte that ionizes or dissociates completely 1. All water soluble ionic compounds dissociate completely, therefore they are strong electrolytes

2. 2. Weak electrolyte: a compound that produces ions upon dissolving but exists in solution predominantly as molecules that are not ionized 1. Most acids are weak electrolytes

4. Dynamic chemical equilibrium: a state in which both forward and reverse reactions continue to occur; they occur at the same rate so there is no net change observed overtime 1. ⇄ 3. Identifying Electrolytes

1. 2. To identify an electrolyte by it's chemical formula; 1. Determine if it is ionic or molecular (covalent) 1. An ionic compound contains a cation (metal or ammonium ion) and an anion (atomic or polyatomic) 2. If it is not ionic, it is molecular; therefore you need to figure out if it is an acid. 1. Acids are generally written with the ionizable hydrogens first 2. Carboxylic acids are often written with their ionizable hydrogens written last 3. If it is an acid, it is an electrolyte. 1. If it is one of the strong electrolytes acids, it’s a strong electrolyte 2. If its an acid not listed it is a weak acid therefore a weak electrolyte 4. If it is not an acid, you have to figure out if it is a weak base

1. Many weak bases are related to ammonia in that they consist of a N atom bonded to a hydrogen and/or carbon atoms 5. If the molecular compound is neither an acid nor a weak base it is a nonelectrolyte 2. Precipitation Reactions 1. Intro 1. Precipitate: an insoluble solid product that separated from a solution 2. Precipitation reaction: a chemical reaction in which a precipitate forms 1. Precipitation reactions usually involve ionic compounds, but a precipitate does not form every time two solutions of electrolytes are combined 2. Whether or not a precipitate forms depends on the solubility of the products 2. Solubility Guidelines for Ionic Compounds in Water 1. Hydration: the process by which water molecules surround solute particles in an aqueous solution 1. Water is an excellent solvent for ionic compounds because H2O is a polar molecule 2. Solubility: the maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature 1. Not all ionic compounds dissolve in water; it depends on the relative magnitudes of water molecules attraction to ions and the ions attraction to one another 1. If the water molecules attraction for the ions exceeds the ions attraction to one another, then the ionic compound will dissolve 2. If the ions attraction to each other exceeds the water molecules attraction to the ions, then the ionic compound won't dissolve

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1. 2. Molecular equations: a chemical equation written with all compounds represented by their chemical formula 1. Steps 1. Write the formulas for the reactants, and then write the formulas for the compounds that would form if the cations in the reactants were to trade anions 2. Then write the formula for one product by combining the cation from the first reactant with the anion from the second reactant 3. Then write the formula for the other product by combining the cation from the second reactant with the anion from the first 4. Then balance the equation 5. Then determine which of the products, if any, will precipitate from solution by using the solubility guidelines for ionic compounds 2. Example

1. 3. Ionic equations: a chemical equation in which all strong electrolytes are shown as ions 1. Soluble ionic compounds are strong electrolytes, they exist in a solution of hydrated ions rather than as formula units 2. Example

1. 4. Net Ionic Equations 1. Spectator ions: an ion that does not participate in the reaction and appears on both sides of the equation

1. Spectator ions cancel each other out

2. 2. Net ionic equation: chemical equation in which spectator ions have been removed 1. It tells us what actually happens when you combine solutions 2. The steps necessary to determine the molecular, ionic, and net ionic equations for a precipitation reaction are as follows: 1. Write and balance the molecular equation, predicting the products by assuming cations trade anions 2. Write the ionic equation by separating strong electrolytes into their constituent ions 3. Write the net ionic equation by identifying and canceling spectator ions on both sides of the equation 4. *if both reactions are strong electrolytes, all the ions are spectator ions; therefore there is no net ionic equation and no reaction takes place 5. Acid Base Reactions 1. Strong Acids and Bases

1. 2. The strong acids are the ones from the list 3. The strong bases are the hydroxides of group 1A and 2A metals 2. Bronsted Acids and Bases 1. Proton refers to a hydrogen atom that has lost its electron (hydrogen ion) 1. Bronsted Acid: proton donor

1. Monoprotic acids: each acid molecule has one proton to donate 1. Most strong acids 2. Diprotic acids: each acid molecule has two protons to donate 1. Only H2SO4 3. Triprotic acids: each acid molecule has three protons to donate 1. Less common than mono and diprotic acids 4. Polyprotic acids: acids with more than one proton to donate 2. Bronsted Base: proton acceptor 3. Acid Base Neutralization 1. Neutralization reaction: a reaction between an acid and a base 1. An aqueous acid base reaction produces water and a salt (an ionic compound made up of a cation from a base and the anion from an acid) 2. A compound in which the anion is an oxide is not considered a salts 6. Oxidation- Reduction reactions (redox reactions): a chemical reaction in which electrons are transferred from one reactant to another 1. Intro 1. If an atom is oxidized, it loses electrons

1. 2. If an atom is reduced, it gains electrons

1. 3. Half reaction: the separated oxidation and reduction reaction that make up the overall redox reaction (these two equations represent a half reaction)

1. 2. Vocab 1. Oxidation is the loss of electrons.

1. Oxidizing agent accepts the electrons, causing the other to be oxidized 2. Reduction is the gain of electrons. 1. Reducing agent donates electrons, causing the other to be reduced 3. Oxidation number (oxidation state): the charge an atom would have if electrons were transferred completely. 1. Oxidation numbers allow us to identify elements that are oxidized and reduced at a glance. 1. Elements that show an increase in oxidation number, are oxidized 2. Elements that show a decrease in oxidation number are being reduced. 2. Rules of assigning oxidation numbers: 1. The oxidation number of any element in its elemental form, is zero 2. The oxidation numbers in any chemical species must sum to the overall charge on the species. The oxidation number of a monatomic ion is equal to the charge on the ion.

3. 4. Oxidation of metals in aqueous solutions 1. Displacement reaction: reaction in which two reactants trade components (double displacement) or where a component of a reactant is removed (single displacement) 1. Active metals: alkali and alkaline earth metals 1. These metals are so reactive that they are not found in nature in their elemental forms

2. Noble metals: metals such as platinum, gold, and silver, have little tendency to react 3. Activity series: a list of metals arranged from top to botton in order of decreasing ease of oxidation

4. 2. Reactions in which hydrogen is reduced to hydrogen gas are known as hydrogen displacement reactions 5. Balancing simple redox equations 1. Half reaction method: 1. Determine if the reaction will occur. 2. Add the half reactions, the electrons will cancel and you will get the balanced overall equation.

2. 6. Other types of redox reactions 1. Combination reactions: the formation of a product when its constituent elements can involve oxidation and reaction.

1. 2. Decomposition reactions: the breakdown of a reactant into its components can also be a redox reaction

1. 2. Disproportionation reaction: in which one element undergoes both oxidation and reduction

1. 3. Combustion reaction is a redox process

1. 7. Oxidation numbers of elements in compounds arranged according to their positions in the periodic table

1. 8. BALANCING ANY REDOX REACTIONS (CH19) STEPS 1. Determine if the equations is balanced or not 1. If it is balanced, it has the same number of atoms of each element on both sides of the equation

2. It also has the same amount of overall charge on both sides of the equation 2. Half reaction method 1. Separate the unbalanced reaction into half reactions 1. Oxidation half reaction 2. Reduction half reaction 2. Balance each half reaction with regard to atoms other than oxygen and hydrogen 3. Balance the oxygen by adding H2O +

4. Balance the hydrogen by adding H

5. Balance the charge by adding electrons 6. Get the same number of electrons in both equations by multiplying by x 7. Add the equations together (the electrons will cancel) and you have the reaction 8. Then check your work by making sure you have the same amount of each atom on each side and equal charges 3. If the reaction is in basic solution, there are two additional steps + 1. For each H ion, add one OH- to both sides of the equation 2. Make any additional cancellations made necessary by the new H2O molecules 7. Concentration of solutions 1. Intro 1. Concentration (of a solution): the amount of solute dissolved in a given quantity of solvent or solution. 1. Qualitative terms in concentration: 1. Concentrated: containing a higher ratio of solute to solvent 2. Dilute: containing a higher ratio of solvent to colute 2. Molarity (molar concentration): 'M ' number of moles per solute per liter of solution 1. Molarity= moles solute/ liters solution 2. Steps to determine molarity: 1. Convert the mass of the solute given into moles and divide that molar number by the volume of the solution given 3. To determine the volume of a solution that contains a certain amount of moles: 1. Divide the moles of solute by the molarity 4. To determine the number of moles in a given volume of solution:

1. Multiply the volume by the molarity 3. Dilution: the process of preparing a less concentrated solution from a more concentrated one. 1. Steps to...