Chapter 4: Types of Chemical Reactions and Solution Stoichiometry • Mr. Redmond
Aqueous Solutions • dissolved in water • Properties: Electrical Conductivity • Strong Electrolytes- conducts well • Weak Electrolytes- conducts little • Nonelectrolytes- does not conduct
Strong Electrolyte • Substances that completely ionize when dissolved in water • Types: • Soluble Salts • Strong Acids • Strong Bases
Soluble Salts • NaCl dissolved in water • Practically all of the sample becomes Na+ and Cl- ions
Acids (Sour) • Arrhenius states: an acid is a substance that produces H+ ions (protons) when it is dissolved in water • HCl, HNO3, and H2SO4 all virtually ionize when placed in water, therefore are considered strong acids.
Bases (Bitter) • When dissolved in water it produces OH-, hydroxide. • Strong bases: NaOH, KOH
Weak Electrolytes • When placed in water they produce few ions. • Weak Acid • Weak Base
Weak Acid • Acetic Acid, dissociates only to a slight extent in an aqueous solution. Only about 1% of its molecules ionize. • HC2H3O2(aq) H+(aq) + C2H3O2-(aq)
Weak Base • Ammonia solution is basic because it produces some OH- ions • NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)
Nonelectrolytes • Substances that dissolve but do not dissolve into ions that can conduct electricity • Ethanol, C2H5OH and sucrose, C12H22O11
Molarity • Molarity= moles of solute per volume of solution in liters • M = Molarity = (moles of solute)/(liters of solution) • Solute- a substance dissolved in a liquid • Solution- a homogeneous mixture
Sample Ex. 4.2 • You dissolve 1.56 g of gaseous HCl in enough water to make 26.8 mL of solution. Find the molarity.
Sample Ex. 4.2 cont. • First we calculate the number of moles of HCl...... • Change volume from mL to L....... • Now divide and find Molarity.......
Sample Ex. 4.4 • Calculate the number of moles of Cl- ions in 1.75 L of 1.0 x 10-3 M ZnCl2 • Formula: ZnCl2(s) Zn2+(aq) + 2Cl-
Sample Ex. 4.4 cont. • You have 1.0 x 10-3 M ZnCl2 • After it dissociates you have 1.0 x 10-3 M Zn2+ and 2.0 x 10-3 M Cl- • Use the known information to calculate moles of Cl-
Sample Ex. 4.5 • Typical blood serum is about 0.14 M NaCl. What volume of blood serum contains 1.0 mg NaCl?
Sample Ex. 4.5 cont. • How many moles of NaCl are in 1 mg NaCl? • What volume of 0.14 M NaCl solution contains the number of moles of NaCl in 1 mg NaCl?
Sample Ex. 4.6 • To analyze the alcohol content of a certain wine, a chemist needs 1.0 L of 0.200 M K2Cr2O7 (potassium dichromate) solution. How much solid K2Cr2O7 must be weighed out to make this solution?
Sample Ex. 4.6 cont. • Determine the moles of potassium dichromate required. • Convert moles into grams
Dilutions • Most times when you purchase chemicals for a lab they come in a concentrated form call stock solutions. • Water is added to these to give the desired molarity of the particular solution
Dilution • Important to understand that: moles of solute after dilution = moles of solute before dilution • For example: if we need 500 mL of 1.00 M acetic acid from a 17.4 M stock solution of acetic acid, we would need to dilute it.
Dilution • First, determine the number of moles of acetic acid in the final solution...... • We then use the volume of 17.4 M acetic acid that contains the calculated amount of moles • We then use this information to solve for the volume
Sample Ex. 4.7 • What volume of 16 M sulfuric acid must be used to prepare 1.5 L of a 0.10 M H2SO4 solution?
Sample Ex. 4.7 • Determine moles of H2SO4 in 1.5 L of a 0.10 M H2SO4 • Find the volume of 16 M H2SO4 that contains 0.15 mol H2SO4
Dilution • The equation: M1V1 = M2V2 , may help you remember that the moles before dilution is equal to the moles after dilution • Repeat the last example using this equation
Dilution • M1V1 = M2V2 • M1=16M, M2= 0.10M, V2=1.5 L • Solve for V1
Types of Reactions • Precipitation reactions • Acid-base reaction • Oxidation-reduction reaction
Precipitation Reactions • Sometimes when two solutions are mixed an insoluble substance is formed, this is called a precipitation reaction • The solid substance that separates from the solution is called the precipitate
Precipitation Reactions • Say we perform a precipitation reaction with an aqueous solution of potassium chromate K2CrO4(aq), which is yellow, and mix it with a colorless aqueous solution containing barium nitrate Ba2(NO3)2(aq) • When these are mixed a yellow precipitate forms
Precipitation Reactions What is the yellow solid forming?
Precipitation Reactions • Remember in virtually every case, when a solid containing ions dissolves in water, the ions separate • From this we know that we have K+, CrO42-, Ba2+, and NO3-
Precipitation Reactions • The reaction is: K2CrO4(aq) + Ba(NO3)2(aq) product • It may be easier to see what is happening if we write the equation a little different 2K+(aq)+CrO42-(aq)+Ba2+(aq)+2NO3-(aq) product • What are the different ways these ions could combined?
Precipitation Reactions • Here are our choices: K2CrO4, KNO3, BaCrO4, or Ba(NO3)2 • We can quickly exclude K2CrO4 and Ba(NO3)2 since they are the reactants • It takes a little background knowledge to figure the rest out
Precipitation Reactions • K+ ion and the NO3- ion are both colorless, thus KNO3 would precipitate white. • CrO42- ion is yellow as noted earlier thus the yellow solid must be BaCrO4 • But what happened to K+ and NO3-?
Precipitation Reactions • The other ions are left dissolved in the solution. If we removed our precipitate and then dissolved the water we would find KNO3(s) left in the beaker
Sample Ex. 4.8 • Use the table just given to solve the problems. Predict what will happen when you mix the following pairs. • KNO3(aq) and BaCl2(aq) • Na2SO4(aq) and Pb(NO3)2(aq) • KOH(aq) and Fe(NO3)3(aq)
Sample Ex. 4.8 • Split up the ions and pair them. The table show that KCl and Ba(NO3)2 are soluble in water, thus no precipitate forms. • NaNO3 is soluble but PbSO4 is not. • K+ and NO3- salts are soluble but Fe(OH)3 is only slightly soluble, thus it will precipitate
Describing Reactions in Solutions • formula equation • complete ionic equation • net ionic equation
Formula Equation • The typical equation we normally write • K2CrO4(aq) + Ba(NO3)2(aq) BaCrO4(s) + 2KNO3(aq)
Complete Ionic Equation • In a complete ionic equation, all the substances that are strong electrolytes are represented as ions • 2K+(aq)+CrO42-(aq)+Ba2+(aq)+2NO3-(aq)BaCrO4(s) + 2K+ + 2NO3-
Net Ionic Equation • A net ionic equation only includes those solution components directly involved in the reaction. We do not write the spectator ions (K+ and NO3-) • Ba2+(aq) + CrO42-(aq) BaCrO4(s)
Sample Ex. 4.9 • For the following reaction, write the formula equation, the complete ionic equation, and the net ionic equation. • Aqueous potassium chloride is added to aqueous silver nitrate to form a silver chloride precipitate plus aqueous potassium nitrate
Stoichiometry of Precipitation Reaction • Just like in Chapter 3, we first convert all quantities into moles • Second, we form the proper molar ratio using the coefficients of the balanced equation • Use the limiting reactant when necessary
Stoichiometry of Precipitation Reaction • Special attention needs to be given to what reaction actually occurs. Use the complete ionic formula and your background knowledge of the reactants to determine the reaction • We must use the molarity and volume to determine the moles of reactant
Sample Ex. 4.10 • Calculate the mass of solid NaCl that must be added to 1.50 L of a 0.100 M AgNO3 solution to precipitate all the Ag+ ions in the form of AgCl.
Sample Ex. 4.10 • Write the complete ionic equation • Refer to the solubility table • Determine what the spectator ions are and what compound is the precipitate • Convert molarity and volume to moles • Use the proper molar ratio then convert to grams
Acid-Base Reactions • Arehenius’ concept of acids and bases • Acids produce H+ ions when dissolved in water • Bases produce OH- ions when dissolved in water • Not all acids or bases have H+ or OH- so a more general definition is needed
Acid-Base Reactions • Bronsted-Lowery Model • Acids are proton donors • Bases are proton acceptors • How do we predict acid-base reactions?
Acid-Base Reactions • Take the example of mixing solutions of HCl and NaOH. We know that HCl is a strong acid and NaOH is a strong base. • Write the ions that are present and look at the solubility table, will NaCl precipitate? • Because water is a nonelectrolyte, large quantities of H+ and OH- ions cannot coexist in the solution. What happens?