Chapter 4: Reactions in Aqueous Solutions

A sample of 70.5 mg potassium phosphate is added to 15.0 mL of 0.050 M silver nitrate, resulting in the formation of a precipitate. a) write the molecular equation b) What is the limiting reaction? c) calculate the theoretical yield, in grams, of the precipitate that forms.

K3PO4 (ag) + 3AgNO3 (aq) = Ag3PO4 (s) + 3KNO3 (aq) 3.32 x 10-4 K3PO4 7.5 X 10 -4 aGno3 AgNO3 is the limiting factor .00075AgNO3 moles (1 mol Ag3PO4/3 mol AgNO3) = 2.5 E-3 2.5 e-4 moles (418.6046 g Ag3PO4/1 mole) = .10465115g

Solvation

The process of surrounding solute particles with solvent particles to form a solution

Tiration

The process, operation, or method of determining the concentration of a substance in solution by adding to it a standard reagent (standard and indicator) of known concentration in carefully measured amounts until a reaction of definite and known proportion is completed, as shown by a color change or by electrical measurement, and then calculating the unknown concentration.

molecular equation

a reaction equation that shows the complete chemical formulas of all reactants and products

neutralization reaction

a reaction in which an acid and a base react in an aqueous solution to produce a salt and water net ionic - H+ (aq) + OH- (aq) = H2O (l)

Standard solution (titrant) How to measure?

a solution of known concentration measure with burette so exact amount can be determined

net ionic equation

an equation for a reaction in solution showing only those particles that are directly involved in the chemical change spectator ions removed charges must be the same on both side

oxidation-reduction reaction

any chemical change in which one species is oxidized (loses electrons) and another species is reduced (gains electrons); also called redox reaction OIL RIG

When writing oxidation number for a ion

consider the charge of the ion those electrons must be "left over" SO4 (2-) Oxidation number of Sulfur O = -8 S= +6

What is the molar concentration of each ion present in a 0.025 M aqueous solution of calcium nitrate?

mol NO3-/L = (0.025 mol Ca(NO3)2/L)(2 mol NO3-/1 mol Ca(NO3)3) 0.050 M NO3 Ca2+ = .025 M

moles =

molarity x volume

What types of chemical reactions have be conducted with a titration?

neutralization, precipitation or oxidation-reduction reactions

equivalence point

the point at which the two solutions used in a titration are present in chemically (stoichiometrically) equivalent amounts

Dilution

the process of adding solvent to lower the concentration of solute in a solution

If solubility is less than 0.01 mol/L then

the substance is considered insoluble the attraction between the oppositely charged ions in the solid is too great for water molecules to separate the ions (substance is mostly not dissolved)

Is ammonia a strong or weak electrolyte?

weak about 1% of NH3 makes NH4 and OH- ions

How are reactions with weak electrolytes represented?

with half arrows because they are weak reactants and products go backward and forward to reach equilibrium

How do molecular substances dissolve?

without forming ions most molecular compounds are non-electrolytes

The quantity of Cl- in a municipal water supply is determined by titrating the sample with Ag+. The precipitation reaction taking place during the titration is: Ag+ (aq) + Cl- (aq) = AgCl (s) a) How many grams of chloride ion are in a sample of the water if 20.2 mL of 0.100 M Ag+ is needed to react with all the chloride in the sample? b) If the sample has a mass of 10.0g , what percentage of Cl- does it contain?

.071609 g Cl- 0.717% Cl-

How to write a net ionic equation

1. Balanced molecular equation 2. complete ionic equation (only strong electrolytes dissociate 3. cancel out elements that are on both signs (you cannot cancel elements out in a compound)

Oxidation Number Rules

1. Each atom in a pure element = 0 2. Monotonic ions = charge on the ion 3. F = -1 (always!) 4. Oxygen = -2 5. Group 1A = +1 (unless in elemental form) 6. Group 2A = +2 (unless in elemental form) 7. Neutral compounds - sum of oxidation #s = 0 8. Polyatomic ions - sum of oxidation #s = ion charge Exceptions: - other halogens = positive oxidation # when combined with oxygen - in peroxides (Na2O2) and superoxides (KO2) = -1, -0.5 5. Hydrogen = +1 nonmetals, -1 metals

Steps to balance metathesis reaction

1. Use chemical formulas of reactants to determine which ions are present 2. Write chemical formula of products by combining cation from one reactant with anion of the other, using ionic charges to determine the subscripts in the chemical formula 3. Check water solubilities of products. For precipitation reaction to occur, at least one product must be insoluble in water 4. Balance the equation -transitional metal will not change forms during exchange/must make anion match

How many grams of Na2SO4 are there in 15 mL of .50 M Na2SO4? How many mililiters of .50M Na2SO4 solution are needed to provide 0.038 mol of this salt?

1.1 g 76 mL

How many mL of 3.0 M H2SO4 are needed to make 450 mL of 0.10 M H2SO4?

15 mL

Oxidation number of Ba in BaO2

2+

One commercial method used to peel potatoes is to them in a NaOH solution for a short time and then remove the potatoes and spray off the peels. The NaOH concentration is normally 3 to 6 M, and the solution must be analyzed periodically. In on such analysis, 45.7 mL of .500 M H2SO4 is required to neutralize 20.0 mL of NaOH solution. What is the concentration of the NaOH solution?

2.28 M NaOH

Grams of Na2SO4 are required to make .350 L of .500 M Na2SO4 SOLUTION?

24.6 G Na2SO4

Oxidation number of Cr in Cr2O7 (2-)

6+

indicator

A compound that changes color in the presence of an acid or a base

nonelectrolyte

A substance that dissolves in water to give a solution that does not conduct an electric current

most common weak base

Ammonia (NH3) reacts with water to form OH-

salt

An ionic compound made from the neutralization of an acid with a base. any ionic compound whose cation comes from a base Na+ from NaOH and whose anion comes from an acid Cl- from HCl

Electrolyte

An ionic compound whose aqueous solution conducts an electric current

Predict the identity of the precipitate that forms when aqueous solutions of BaCl2 and K2SO4 are mixed Write the balanced equation

BaSO4 BaCl2 (aq) + K2SO4 (aq) = BaSO4(s) + 2KCl(aq)

insoluble anions

CO3, PO4 (except with NH4+ and alkali metal cations) S, OH- (except with NH4 , alkali metals, Ca,Sr and Ba insoluble anion forms precipitate insoluble solid

Write the net ionic equation for the precipitation reaction between aqueous solutions of calcium chloride and sodium carbonate are mixed

Ca2+(aq) + CO3(2-) (aq) = CaCO3(S)

Bases

Compounds that reduce the concentration of hydrogen ions in a solution. accept H+ (react with) produce OH- hydroxide ions when they dissolve in water NaOH, KOH, Ca(OH)2 - ionic hydroxide compounds NH3

Copper metal oxidized by Silver ion

Cu (s) + 2 Ag+ (aq) + = Cu 2+ (aq) + 2 Ag (s)

List the strong acids

HCl, HBr, HI, HClO3, HClO4, HNO3, H2SO4 strong electrolytes

chemical equilibrium

In a chemical reaction, the state in which the rate of the forward reaction equals the rate of the reverse reaction, so that the relative concentrations of the reactants and products do not change with time.

spectator ions

Ions that do not take part in a chemical reaction and are found in solution both before and after the reaction can be removed

Molarity equation

M = moles of solute/liters of solution

equation that shows relationship between moles in concentrated solution and dilute solution

M concentrated x V concentrated = M diluted x V diluted

Write balanced molecular and net ionic equation for redox reaction between magnesium and cobalt (II) sulfate Who is oxidized, who is reduced

Mg (s) + CoSO4 (aq) - MgSO4 (aq) + Co (s) Mg (s) + Co 2+ (aq) = Mg 2+ (aq) + Co (s) Mg oxidized Co reduced

Use the equation and predict products and if insoluble precipitate forms? Mg(NO3)2 (aq) + 2NaOH (aq)

Mg(OH)2 (s) + 2NaNO3 (aq)

Will an aqueous solution of iron (II) chloride oxidize magnesium metal? Write the balanced molecular and net ionic equations.

Mg(s) + FeCl2(aq) = MgCl2(aq) + Fe(s) Mg(s) + Fe2+ (aq) = Mg2+ (aq) + Fe(s)

Cannot use ______ ________ when converting between grams and moles in a solution. What must be used instead.

Molar mass Because it is a solution and not a pure substance. moles of solute = M x V if you know moles of one reactant you must determine moles of the other reactant if you are solving for that

Does a reaction occur when NiCl2 is added to a test tube containing Zn(NO3)2

NO, Zinc cannot be oxidized further

Oxidation

The loss of electrons from a substance involved in a redox reaction. named oxidation because metal reactions with oxygen were the 1st to be studied/many metals react with O2 to form metal oxides

aqueous solution

a solution in which water is the solvent

which metals are the most active metals?

alkali metals and alkaline earth metals easiest metals to oxidize

activity series of metals list

any metal can be oxidized by the ion of an element below it lithium Potassium Barium Calcium Sodium Magnesium Aluminium Manganese Zinc Chromium Iron Cobalt Nickel Tin Lead Hydrogen Copper Silver Mercury Platinum Gold nothing below hydrogen can react with an acid and be oxidized by H+ to form H

When calculating molarity for separate ions make sure to

calculate in terms of the amount of ions 0.025 M of Ca(NO3)2 Ca = 0.025 M (NO3)2 = 0.050 M

Acid

compound that forms hydrogen ions (H+) in aqueous solution H+ is simply a proton acids called proton donors

When writing net ionic or complete ionic equation weak acids?

do not go through ionization in the reactant phase

Solubility and strong or weak electrolyte

don't confuse CH3COOH is extremely soluble in water but a weak electrolyte Ca(OH)2 is not very soluble in water but a strong electrolyte - what little does dissolve dissociates completely

Only write oxidation number for

element that has been requested the overall molecule is neutral (unless ion)

reduction

gain of electrons

solvated ions

ions are surrounded by water molecules write as Na+ (aq) Cl- (aq)

Using moles in dilute solution to calculate liters of concentrated solution to provide the same amount of moles

moles in dilute = (L solution) (molarity mol/L) Liters of concentrated solution to get the same amount of moles in diluted = (moles in diluted)(molarity L/mol)

If every ion in a complete ionic equation is a spectator?

no reaction occurs

CH3COOH ionization

only H from -OH group can be ionized in water

When writing oxidation number if there is more than one atom

only write the oxidation number for one atom P2O5 O=-10 P = +5

Are all common ionic compounds of alkali metal group and ammonium ions soluble or insoluble in water?

soluble in water

Taste of acids

sour taste

Molecules can be (strong, weak, non-electrolytes)

strong acids weak acids or bases or non-electrolyte

List the strong bases

strong electrolytes, all soluble Group 1 (metal hydroxides): LiOH, NaOH, KOH, RbOH Group 2 (metal hydroxides) CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

When solvent is added to a solution, what happens to the number of moles?

they do not change moles solute before dilution = moles solute after dilution

weak acids and bases are also

weak electrolytes

How many grams of Ca(OH)2 are needed to neutralize 25.0 mL of 0.100 M HNO3?

0.100 M = moles/.025L = .0025 moles HNO3 Ca(OH)2 + 2HNO3 = 2H2O + Ca(NO3)2 Grams of Ca(OH)2 = .0025 moles of HNO3(1 mole Ca(OH)2/2 moles 2HNO3)(74 g Ca(OH)2/ 1 mol Ca(OH)2 = .0925g Ca(OH)2

Oxidation number of H in NaH

-1

Oxidation number rules

1. Atom in Elemental Form is neutral 2. Monoatomic ion - oxidation number is the charge 3. Nonmetals - usually negative - oxygen -2 unless peroxides (O22- ion) have -1 - hydrogen +1 bonded to nonmetal -1 bonded to metal -Fluorine always -1/other halogens -1 in binary compounds but positive when combined with oxygen in oxyanions 4. Sum of the oxidation number - all atoms in neutral compound is zero - in polyatomic ion = equals charge of polyatomic ion -H3O+ = each H +1 + O 2- = +1

How to predict if a precipitate forms?

1. Note ions present in reactants 2. Consider the possible cation-anion combinations 3. Use known soluble and insoluble ions to see if any combinations are insoluble

Write the balanced equation for a reaction between aqueous solutions of acetic acid (CH2COOH) and barium hydroxide Ba(OH)2 B) Complete ionic equation C) Net ionic equation

2CH2COOH(aq) +Ba(OH)2(aq) = 2H2O(l) + Ba(CH2COO)2(aq) 2CH2COOH(aq) + Ba2+ (aq) + 2OH- (aq) = 2H2O (l) + Ba2+ (aq) + 2CH2COO-(AQ) CH2COOH(aq) + OH-(aq) = H2O(l) + CH2COO-(aq)

The most stable metals

8b to 1B used to make coins and jewelry

precipitate

A insoluble solid that forms from a solution during a chemical reaction. Pb(NO3)2(aq) + 2KI(aq) = PbI2(s) + 2KNO3(aq)

Solubility

A measure of how much solute can dissolve in a given solvent at a given temperature.

Concentration

A measurement of how much solute exists within a certain volume of solvent greater amount of solute = higher concentration

Consider solutions in which 0.1 mol of each of the following compounds is dissolved in 1L of water: Ca(NO3)2 (calcium nitrate), C6H12O6 (glucose), NaCH3COO (sodium acetate) and CH3COOH (acetic acid). Rank the solutions in order of increasing electrical conductivity, knowing that the greater number of ions in solution, the greater the conductivity.

C6H12O6, CH3COOH, NaCH3COO, Ca(NO3)2

Classify these dissolved substances as a strong electrolyte, weak electrolyte, or nonelectrolyte: CaCl2, HNO3, C2H5OH (ethanol), HCOOH (formic acid), KOH

CaCl2, Strong electrolyte HNO3, Strong electrolyte C2H5OH (ethanol), nonelectrolyte HCOOH (formic acid), weak electrolyte KOH strong electrolyte

Soluble Anions with exceptions

Cl-, Br-, I- (not with Ag+, Hg2(2+), Pb(2+) SO4(2-) (not with Sr2+, Ba2+, Hg2(2+) or Pb (2+)

What compound precipitates when aqueous solutions of Fe2(SO4)3 and LiOH are mixed? Write the balanced equation for the reaction.

Fe(OH)3 Fe2(SO4)3(aq) + 6LiOH(aq) = 2Fe(OH)3 (s) + 3Li2SO4(aq)

which anions are always soluble?

NO3- and CH3COO-

Other bases that react with H+ to form molecular compounds

S2- form H2S CO32- form CO2 react with acids to form gases that have low solubility in water 2HCl (aq) + Na2S (aq) = H2S (g) + 2NaCl (aq) HCl (aq) + NaHCO3 (aq) = NaCl (aq) + H2O (l) + CO2 (g)

When do precipitation reactions occur?

When pairs of oppositely charged ions ions attract each other so strongly that they form an insoluble ionic solid

weak electrolyte

a compound that dissociates only to a small extent in aqueous solution; most solute in the form of neutral molecules CH3COOH only about 1% dissociates into H+ (aq) CH3COO-(aq) poor conductor of electricity

precipitation reaction

a reaction in which an insoluble substance forms and separates from the solution

metathesis reaction 2 examples

a reaction that involves the exchange of parts between two compounds also called exchange reaction precipitation reactions show this and neutralization reactions between acids and bases

activity series of metals

a series of elements that have similar properties and that are arranged in descending order of chemical activity; examples of activity series include metals and halogens

If you were to draw diagrams representing aqueous solutions of a. NiSO4 b. Ca(NO3)2 c. Na3PO4 d. Al2(SO4)3 How many anions would you show if each diagram contained six cations?

a. 6 b. 12 c. 2 d. 9

Classify the following compounds as soluble or insoluble in water a. Cobalt (II) hydroxide b. Barium nitrate c. ammonium phosphate

a. insoluble b. soluble c. soluble

Classify these ionic compounds as soluble or insoluble in water a. sodium carbonate Na2CO3 b. lead sulfate PbSO4

a. soluble b. insoluble

molecular compounds with ions are typically

acids HCl (g) dissolves to form HCl (aq) it dissociates to form H+ (aq) and Cl- (aq)

strong electrolyte

all or nearly all of the solute exists as ions conduct electricity well NaCl all water soluble ionic compounds and a few molecular compounds compounds with ammonium are an exception

monoprotic acid

an acid that can donate only one proton (hydrogen ion) per molecule HCl, HNCO3

diprotic acid

an acid that can donate two protons per molecule H2SO4 Ionization of diprotic acids occurs in two steps

complete ionic equation

an equation that shows dissolved ionic compounds as dissociated free ions strong electrolytes shown an ions

Ammonia is a common ________ and how this occurs?

base when added to water it accepts H+ from water molecule and produces OH- ion

Taste of bases

bitter, chalky

concentration of an electrolyte

concentration of ions the dissolve in a solution depends on the chemical formula of a compound 1.0 M solution of NaCl is 1.0 M Na+ and 1.0 M Cl- Concentration of electrolyte solution can be specified as either the compound used to the make the solution or the ions in the solution

Why is solvation important?

help to stabilize ions in a solution and prevents cations and ions from rejoining because ions and their shell of water molecules are free to move they disperse evenly throughout the solution

displacement reaction metal with acid, produce?

ion in solution is displaced through oxidation of an element many metals undergo displacement reactions with acids, producing salts and hydrogen gas

Does pure water conduct electricity?

no it must contain ions

H2SO4 ionization in water

only 1st ionization is complete 2nd is not so aqueous solution of sulfuric acid contains mixture of H+, HSO4- , and SO4(2-)

What type of reaction occurred below (determine spectator ions, who is oxu Mg(s) + 2HCl (aq) = MgCl2(aq) + H2(g)

single displacement reaction Mg Oxidized +2 H reduced 0 Spectator ions - Cl2

All ionic compounds are __________ electrolytes.

strong electrolytes and none are weak or noneletrolytes

Reactivity of acid doesn't just depend on H+ concentration

the anion matters as well Hydrofluoric acid is a weak acid but is very reactive and attacks many substances including glass due to combined reactivity of H+ and F-

corrosion

the deterioration of a metal due to a chemical reaction in the environment metal corroded into metal compound metal looses electron to form cation and will combine with an anion to form an ionic compound

Molarity

the number of moles of solute per liter of solution

How are strong electrolyte chemical reactions typically represented?

with a single arrow because they tend to only go forward (no recombining of ions)