⏱️ August 20, 2020
The second main type of reaction that you learn in this unit is the acid-base neutralization reaction🍊.
To recall, acids are proton donors while bases are proton acceptors. The species that donated the proton becomes the acid’s conjugate base. Similarly, the species that accepted the proton is now the conjugate acid.
Looking at a chemical equation, you should be able to tell what the acid-base pairs are, and picking out the conjugates.
For example🤔, H2O + H2S --> H3O+ + HS-.
First things first, what are the acid-base pairs?
First pair: H2O and H3O+
Second pair: H2S and HS-
Now, which are the acids and which are the bases. A quick way to know would be to figure out which compound in the pair has an extra hydrogen. Since H3O+ has one more hydrogen than H2O, it is the conjugate acid. This makes H2O the base.
Try the second pair on your own😊!
For more on this topic about the Bronsted-Lowry Definition:
📝Read: AP Chemistry - Titrations
There are also these weird agents🥴 called amphiprotic substances. They can both donate and accept protons! An example that you really, really know is H2O, but NH3- is also an amphiprotic substance.
💡Tip - H+ and H3O+ are used synonymously as a proton.
A neutralization reaction occurs when an acid and base react to often form an ionic salt and liquid water. The H+ ion from the acid combines with the OH- from the base to form H2O (l).
You often have to write out the chemical reaction. Let's say the two reactants are HNO3 (aq) and KOH (aq), what are the products💭?
To make things easier on yourself, automatically write out H2O (l)💧. Then, just combine the remaining ions, which would form the salt.
👉 HNO3 (aq) + KOH (aq) --> H2O (l) + KNO3
Using solubility rules, is KNO3 soluble? Or is it a precipitate?
Any compound with NO3 is soluble, so KNO3 is in the aqueous state. 👉 HNO3 (aq) + KOH (aq) --> H2O (l) + KNO3 (aq)
📝Read: AP Chemistry - Net Ionic Equation
When writing a net ionic equation for neutralization reactions, you have to be really careful⚠️ not to dissociate weak acids and bases. Luckily, HNO3 is a strong acid and KOH is a strong base, so we can dissociate both.
📝Read: AP Chemistry - Representation of Solutions for list of strong acids and bases
Complete Ionic Equation: H+ + NO3- + K+ + OH- --> H2O (l) + K+ + NO3-
Eliminate spectator ions, which are K+ and NO3-
👉Net Ionic Equation: H+ + OH- --> H2O (l)
With an acid-base neutralization reaction, you could also find the concentration of ions. With this chemical reaction, what are the concentrations of hydrogen ions and hydroxide ions?
💭In other words, what is [H+]? [OH-]?
Given Information: We have 0.250 M and 28.0 mL of HNO3 and 0.320 M and 53.0 mL of KOH.
Let's find the # of moles of HNO3 and KOH using:
HNO3: 0.250 M = x moles / 0.0280 L
x = 0.00700 moles of HNO3
KOH: 0.320 M = x moles / 0.0530 L
x = 0.0170 moles of KOH
The limiting reactant is the reactant that there is less of. In this case, since there is a one to one ratio for all compounds, HNO3 is the LR.
Concentration of 0?
Since H+ is in both the limiting reactant and H2O, it has a concentration of 0. The spectator ions cannot have a concentration of 0. Remember🤔, they just help the reaction take place.
Half the question is done🥳! [H+] = 0.
Finding the concentration of the excess compound is often the hardest part of the problem. First, we have to find the # of moles reacted by converting the LR into the product.
Again, since everything is one to one, the # of moles reacted is 0.00700.
Then we simply subtract from the number of excess moles we started with, which is 0.0170 moles of KOH.
0.0170 - 0.00700 = 0.010 moles unreacted.
Last but not least, we need a volume! 28.0mL + 53.00mL = 0.081 L
0.010 moles unreacted / 0.081 L = 0.12 M of OH-
[H+] = 0
[OH-] = 0.12
Practice, practice, practice! It's just a lottttt of stoichiometry🙃.
Write the net ionic equation of a reaction between HNO3 and Al(OH)3.
Here are the steps you should take:
Write out the products: H2O + Al(NO3)3
Balance the equation: 3HNO3 + Al(OH)3 --> 3H2O + Al(NO3)3
Write out the states of matter using solubility rules: 3HNO3 (aq) + Al(OH)3 (s) --> 3H2O (l) + Al(NO3)3 (aq)
Al(OH)3 is insoluble! We cannot dissociate it in the next step
Dissociate aqueous substances: 3H+ (aq) + 3NO3 (aq) + Al(OH)3 (s) --> 3H2O (l) + Al+3 (aq) + 3NO3- (aq)
Identify spectator ions: 3H+ (aq) + 3NO3 (aq) + Al(OH)3 (s) --> 3H2O (l) + Al+3 (aq) + 3NO3- (aq)
Cross out spectator ions: 3H+ (aq) + Al(OH)3 (s) --> 3H2O (l) + Al+3 (aq)
✍️ Free Response Questions
AP Chemistry Free Response Questions
⚛️ Unit 1: Atomic Structure and Properties
1.1Moles and Molar Mass
1.2Mass Spectroscopy of Elements
1.3Elemental Composition of Pure Substances
1.4Composition of Mixtures
1.5Atomic Structure and Electron Configurations
1.6Photoelectron Spectroscopy & Graph Interp.
🤓 Unit 2: Molecular and Ionic Compound Structures and Properties
2.0Unit 2 Overview: Molecular and Ionic Bonding
2.1Types of Chemical Bonds
2.2Intramolecular Force and Potential Energy
2.3Ionic Bonding and Ionic Solids
2.4Metallic Bonding and Alloys
2.5Lewis Dot Diagrams
2.6Resonance and Formal Charge
🌀 Unit 3: Intermolecular Forces and Properties
3.0Unit 3 Overview: Intermolecular Forces and Properties
3.2Properties of Solids
3.3Solids, Liquids, and Gases
3.4The Ideal Gas Law
3.5The Kinetic Molecular Theory of Gases
3.6Deviations from the Ideal Gas Law
3.7Mixtures and Solutions
3.8Representations of Solutions
3.9Separation of Solids/Mixtures
3.10Solubility and Solubility Rules
3.11Spectroscopy and the Electromagnetic Spectrum
3.12Quantum Mechanics and the Photoelectric Effect
🧪 Unit 4: Chemical Reactions
4.0Unit 4 Overview: Chemical Reactions
4.1Recognizing Chemical Reactions
4.2Net Ionic Equations
4.4Physical vs. Chemical Changes
4.5Stoichiometry & Calculations
4.6Titrations - Intro and Calculations
4.8Intro to Acid-Base Neutralization Reactions
👟 Unit 5: Kinetics
5.0Unit 5 Overview: Kinetics
5.1Defining Rate of Reaction
5.2Introduction to Rate Laws
5.3Rate and Concentration Change
5.4Writing Rate Laws
5.5Collision Model of Kinetics
5.6Reaction Energy and Graphs w/ Energy
5.7Reaction Mechanisms and Elementary Steps
5.8Writing Rate Laws Using Mechanisms
🔥 Unit 6: Thermodynamics
6.0 Unit 6 Overview: Thermochemistry and Reaction Thermodynamics
6.1Endothermic Processes vs. Exothermic Processes
6.2Energy Diagrams of Reactions
6.3Kinetic Energy, Heat Transfer, and Thermal Equilibrium
6.4Heat Capacity and Coffee-Cup Calorimetry
6.5Phase Changes and Energy
6.6Introduction to Enthalpy of Reaction
6.7Bond Enthalpy and Bond Dissociation Energy
6.8Enthalpies of Formation
⚖️ Unit 7: Equilibrium
🍊 Unit 8: Acids and Bases
8.0Unit 8 Overview: Acids and Bases
8.1Introduction to Acids and Bases
Unit 9: Applications of Thermodynamics
🤺 AP Chemistry Essentials
🧐 Multiple Choice Questions
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