CHEM 119 Fall 2026 - Chapter 4 (10022026)
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Overview
Alicia Altemose reviews the Canvas/Excel grade calculator and course deadlines, then teaches CHEM 119 methods for predicting precipitation and acid-base reactions and writing net ionic equations. Examples including PbI2 formation, AgCl precipitation, strong and weak acid/base behavior, and ammonia illustrate which substances dissociate; the class closes with oxidation-number rules and OIL RIG.
Key takeaways
- A double-displacement equation predicts a precipitation reaction only when the solubility rules show that at least one product is an insoluble solid; otherwise, all aqueous ions remain spectators and there is no reaction.
- To write a net ionic equation, dissociate aqueous strong electrolytes, keep solids and liquids intact, and cancel only ions that appear unchanged on both sides.
- The net ionic equation for any strong acid-strong base neutralization is H+(aq) + OH-(aq) → H2O(l), because the soluble salt's ions cancel as spectators.
- Weak acids and bases remain molecular in ionic equations; for HCl reacting with NH3, chloride cancels and the net ionic reaction is H+(aq) + NH3(aq) → NH4+(aq).
- Oxidation numbers identify electron transfer: elemental substances have value 0, oxygen is usually -2, neutral compounds sum to 0, and OIL RIG links oxidation to electron loss and reduction to electron gain.
- The course grade calculator uses desktop Excel fields for current and projected scores; a final-exam score can replace the lowest exam, and participation above 70% counts as full credit.
Chapters
- Download the grade calculator from Canvas Student Resources and open it in desktop Microsoft Excel; yellow cells are the editable fields.
- Enter the mini-exam, Exam 1, lab, ALEKS homework, and participation percentages; participation is calculated from 34 possible points across listed activities.
- A final exam score higher than the lowest exam replaces that exam, and participation above 70% counts as 100%; email Alicia Altemose about suspected ALEKS score mismatches.
- Homework is due Monday night, while drop-in hours take place after class and SI sessions and the Learning Lab resume next week.
- Chapter 4 will finish Monday, followed by Chapter 7; Chapters 5 and 6 are being skipped, and Chapter 7 notes are due to be posted that day.
- Exam feedback and answer keys are expected by Wednesday next week, and a survey offers another opportunity for extra credit.
- In double-displacement reactions, ions exchange partners; HCl is a strong acid and dissociates completely in solution despite not being an ionic compound.
- Strong electrolytes dissociate 100% and include soluble ionic compounds, strong acids, and strong bases.
- The example HCl + NaOH forms soluble NaCl and liquid H2O; for this course, acid-base reactions generally produce water and are called neutralizations.
- A precipitate is an insoluble ionic compound that forms as a solid; mixing aqueous KI and Pb(NO3)2 produces yellow PbI2.
- Aqueous ionic reactants dissociate into K+, I-, Pb2+, and NO3-; two iodide ions combine with each Pb2+ to form PbI2.
- K+ and NO3- remain dissolved as spectator ions, while the PbI2 solid is best represented as an ionic lattice rather than separate PbI2 molecules.
- After swapping partners in NaCl + KI, both possible products, NaI and KCl, remain soluble according to the solubility chart.
- If mixing aqueous ionic compounds produces no solid or other driving product, the ions remain dissociated and no reaction occurs.
- When every species remains an unchanged aqueous ion, there is no net ionic equation because all ions are spectators.
- Mixing aqueous NaCl and AgNO3 forms insoluble AgCl(s) and soluble NaNO3(aq).
- The total ionic equation dissociates aqueous ionic compounds, including NaCl, AgNO3, and NaNO3, but leaves solid AgCl intact.
- Cancel unchanged Na+ and NO3- spectator ions to obtain Ag+(aq) + Cl-(aq) → AgCl(s); include charges and state symbols.
- For LiNO3(aq) and NaC2H3O2(aq), predict the exchanged products and check each against the solubility chart.
- The products remain aqueous, so the mixture has no precipitate, no reaction, and no net ionic equation.
- The practice emphasizes using solubility rather than merely writing balanced double-displacement products to decide whether a reaction occurs.
- Seven strong acids must be memorized because they dissociate completely; soluble ionic compounds and strong bases also appear as ions in total ionic equations.
- Weak acids and weak bases are weak electrolytes and stay together as aqueous molecules when writing ionic equations; HF is a notable weak acid despite containing hydrogen and a halogen.
- Strong bases such as NaOH release OH- by dissociation, while nitrogen-containing compounds are often clues to weak bases; a fluoride solubility-chart inconsistency with ALEKS is also noted.
- Weak base NH3 reacts only partly with water to form NH4+ and OH-; most ammonia remains molecular, so NH3 and liquid H2O are not dissociated.
- For KOH(aq) + HNO3(aq), K+ and NO3- are spectators and the net ionic equation is H+(aq) + OH-(aq) → H2O(l).
- The water-forming equation applies to strong acid-strong base neutralization because both reactants dissociate completely and the soluble salt remains aqueous.
- Strong acid HCl reacts with weak base NH3 to form soluble NH4Cl; Cl- is the spectator ion, leaving H+(aq) + NH3(aq) → NH4+(aq).
- For neutral compounds, oxidation numbers sum to zero; elemental forms have oxidation number 0, monatomic ions use their charge, and oxygen is usually -2.
- OIL RIG means oxidation is loss of electrons and raises oxidation number, while reduction is gain of electrons and lowers oxidation number.
Transcript excerpt
0:10 Howdy. Oh, good morning. Happy Friday. So, uh, I wanted to start before I go through the announcements. Does anybody want me to practice going through the grade calculator? Did you see my announcement? Okay, we'll practice going through it real quick. Mhm. So, if you didn't see my announcement, make sure you check the announcements on Canvas, but it is under the student resources. So, if you click on the grade calculator, and this is being recorded, so you could try it later if you can't keep up right now, which is okay. So, what you want to do is download it. So, it says download. And if your computer doesn't automatically open it in Excel, you'll
0:59 probably want to make sure that you like find it where in your downloads and click to open it with Excel. So, you do need the desktop version of Excel um to do it, which you can do on a Canvas computer if you want. You don't have to do it on the uh on your personal if you don't have it downloaded on your personal. So, at the top, you're going to put in your scores. So, I did not I did not program anything in here to replace your mini exam with your exam one score if it was higher. Um that was a little complicated. So, I didn't program that in here. Um but that will happen. I'm just waiting for everybody to take the
1:46 exam first before I change your mini exam scores. Um, but if it doesn't automatically like let you start editing, you might have to click like enable editing or like save a copy or whatever. Um, but say you got 14 out of 20 on the mini exam and on your uh on Canvas, I think I fixed it.
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Related notes
Summary, takeaways, and chapters were generated by AI from the video's transcript and may contain errors. The video belongs to its creator, Alicia Altemose.