Unit 07 · Acids, Bases & Solutions

Paper investigation sequence and exact evidence record

Scope and safety: All new cases are paper/data investigations, not laboratory procedures. Any physical exercise requires prior educator and safety approval, an approved protocol, suitable facilities and accessibility provisions. Do not improvise acid/base, electrolysis, gas, high-voltage, combustion, toxic-substance or unknown-substance experiments from these tables. Supplied records do not demonstrate hands-on technique or performed lab hours.

Materials and preparation

• [acid-base-intro] Use the two supplied symbolic/data tables, the replacement volumes and concentrations, and the assigned classification/pH sections only.
• [weak-acid] Use weak-acid, acid-structure, the 1e-8 M strong-acid challenge and the dilution transfer; all work is on paper.
• [buffer-capacity] Use buffer-capacity and its fixed final-volume model plus the given base transfer; no real acid, base or buffer preparation is required.
• [titration-solubility] Use titration-solubility, endpoint-records and solubility-records plus the given monoprotic and diprotic equations; no chemicals or apparatus are assigned.

Procedure and schedule

1. [acid-base-intro] Question: When does a proton-transfer mixture leave acid or base in excess, and what evidence distinguishes it from precipitation or weak equilibrium? Prerequisites: Understand mole concentration, mL-to-L conversion, signed ionic charge and acid/base definitions; logarithms are used only after the amount ledger.
2. [acid-base-intro] Design: Change acid and base equivalent amounts; record limiting species, excess concentration and conditional final pH. Controls: Keep monoprotic/monohydroxide stoichiometry, full dissociation, final 25 C and additive-volume assumptions explicit. Replication: Independently check moles, charge and the limiting comparison; recalculation is not a replicate titration or sensor reading.
3. [acid-base-intro] Analysis procedure: Write the net ionic equation, calculate both amounts, subtract the limiting equivalent, divide by total volume and apply the appropriate pH relation. Record: Retain equations, proton donor/acceptor labels, spectator and excess ledgers, units, final volume, assumptions, source/date, weak-base critique and transfer.
4. [weak-acid] Question: At what dilution does a convenient weak-acid approximation contradict material balance, and when must water be included? Prerequisites: Conjugate pairs, logarithms, Ka/Kb/Kw, molarity, quadratic roots and material/charge balance.
5. [weak-acid] Design: Change analytical concentration while holding Ka and temperature fixed; calculate free H3O+, pH and percent ionization. Controls: State the activity approximation, initial conjugate-base amount and when water autoionization is negligible. Replication: Verify physical roots by substitution and compare two solution methods; no actual solution or repeated pH measurement is supplied.
6. [weak-acid] Analysis procedure: Solve the equilibrium, compare sqrt and exact roots, test depletion and autoionization, and distinguish structural strength from concentration. Record: Retain C/Ka/Kw, both roots or rejected root explanation, units, pH/percent chains, approximation checks, structure argument, source/date and transfer.
7. [buffer-capacity] Question: Can two buffers with the same starting ratio respond very differently to the same acid-equivalent challenge? Prerequisites: Moles, strong neutralization, conjugate pairs, logarithms and the weak-acid equilibrium assumptions.
8. [buffer-capacity] Design: Vary total conjugate-pair reserve or sign of added equivalents; compare residual amounts and calculated pH. Controls: Keep Ka, temperature, final volume and ratio-model assumptions explicit; do not confuse matched pH with matched capacity. Replication: Compare independent mole ledgers; four scenarios are not replicate titrations and supply no laboratory repeatability claim.
9. [buffer-capacity] Analysis procedure: Neutralize, check whether both partners remain, select ratio or excess-strong-ion model and assess the neglected weak contribution. Record: Retain initial/change/final moles, final volume, pKa and pH, exhaustion verdict, approximation assessment, source/date and reversed-challenge transfer.
10. [titration-solubility] Question: Which equilibrium model applies in each titration region, and how do endpoint bias and common ions change the interpretation? Prerequisites: Moles, balanced acid/base stoichiometry, Ka/Kb, buffer conditions, hydrolysis, molarity after mixing and solubility powers.
11. [titration-solubility] Design: Base-equivalent amount varies in the curve; added common ion varies separately in the solubility comparison. Controls: Keep temperature, initial acid amount, base concentration and stated activity/speciation approximations explicit; compute each final volume. Replication: Three constructed endpoint volumes illustrate repeatability only. Their mean remains biased relative to the supplied stoichiometric reference.
12. [titration-solubility] Analysis procedure: Build a mole ledger for each volume, select its pH model, graph labeled regions, compute endpoint bias and diluted Qsp, then evaluate assumption failures. Record: Retain curve points with regime labels, neutralization/hydrolysis work, volumes, endpoint mean/range and bias, solubility/Qsp chains, source/date and MX2 transfer.

Record: Label every page with case and dataset IDs, selected readiness level, date and source section. Preserve the independent first attempt, units, assumptions, calculations, uncertainty, feedback and transfer. Cite the specific science criterion; do not sign a practical observation that did not occur. The course-map inventory connects every case to these exact records.

Foundation: typically grades 7-8

• [acid-base-intro] Use the symbolic reactions to identify the proton donor and acceptor in strong neutralization and in ammonia reacting with water. Explain why the silver/chloride contrast is precipitation rather than the listed proton-transfer reaction.
• [weak-acid] Using Relative Strengths of Acids and Bases, identify the conjugate pair and write the HA equilibrium. Explain strength versus concentration, then use the supplied quadratic x to compute pH and percent ionization.
• [buffer-capacity] From Buffers, name the pair that consumes H+ and complete the before/change/after mole ledger for B1. Explain why pKa is not automatically the pH after an unequal pair ratio develops.
• [titration-solubility] Using Acid-Base Titrations, calculate initial acid moles and equivalence volume, assign a model to each titration-solubility row and explain endpoint versus equivalence without using the color change as the definition of chemical equality.

High-school core: typically grades 9-10

• [acid-base-intro] Calculate acid and base amounts from the two solutions, keep a before/after ionic ledger, and find the final excess concentration and pH. Explain what happens to spectator ions and why the result need not be pH 7.
• [weak-acid] Solve the weak-acid quadratic independently and test the square-root/5% approximation. Apply the parallel method to a hypothetical base with Kb = 1.8e-5 and C = 0.1000 M at 25 degrees C, identifying what x now represents.
• [buffer-capacity] Calculate B1 pH from the updated amounts, then compare the high-reserve and low-reserve cases after the same 0.002 mol acid challenge. Explain why similar starting pH does not mean similar capacity.
• [titration-solubility] Calculate the half-equivalence, equivalence and post-equivalence pH values, retaining final volumes. Compare mean endpoint with the true model equivalence, then calculate AgCl solubility with and without added chloride.

Honors extension: typically grades 11-12

• [acid-base-intro] Explain why the ammonia/water equation cannot be treated as complete neutralization with the same shortcut. Identify what extra quantitative information and checks would be needed for its pH, and distinguish that issue from the presence of spectators.
• [weak-acid] Use pH and pOH to derive the charge-balance correction for a 1e-8 M strong acid. Contrast bond-strength and resonance arguments in acid-structure and state why the earlier square-root screen is not a general certification of accuracy.
• [buffer-capacity] Evaluate the exhausted case without taking a logarithm of a negative or zero base amount. Derive the formal HA concentration from the supplied total HA plus A- and final volume, then estimate further dissociation in the remaining strong H+ and assess the leading pH approximation.
• [titration-solubility] Use Precipitation and Dissolution to calculate Qsp after equal-volume mixing and assess pH effects for a salt with a basic anion versus AgCl. For 20.0 mL 0.0500 M H2A titrated to its second equivalence with 0.1000 M OH-, use the balanced two-proton stoichiometry.

History, reading, and writing connection

Use the buffer and titration readings to evaluate a public claim that one pH or one color change establishes a product’s strength, capacity or environmental safety. Cite the relevant section, explain the quantitative limit and avoid testing household or unknown substances.

Write in your own words or use an approved accessible equivalent. Cite a specific assigned section or figure, identify its evidence, and state one limitation or counterargument. Use the AI practice contract only for permitted coaching, never to invent observations or write the assessed response.

Transfer to a new case

[acid-base-intro] Replace the original inputs with 10.0 mL of 0.100 M HCl and 15.0 mL of 0.100 M NaOH. At the same ideal additive-volume and 25 C assumptions, identify the excess species, its concentration and the resulting pH. [weak-acid] Dilute the same HA model to C = 1.00e-5 M at unchanged Ka and temperature. Compare sqrt(KaC) with the total concentration, solve the quadratic and check whether water can still be neglected to a useful first approximation. [buffer-capacity] Start again from B0, but use 0.00300 mol strong OH- instead of H+, at the same 0.100 L final volume. Calculate post-neutralization pair amounts and approximate pH, then state the condition that permits using the ratio. [titration-solubility] Replace AgCl with a hypothetical MX2(s) <-> M2+ + 2X- having Ksp = 4.00e-12 in ideal pure water, without protonation or complexes. Derive molar solubility and explain why sqrt(Ksp) would use the wrong stoichiometry.

Calibration: [acid-base-intro] The amounts are 1.0 mmol acid and 1.5 mmol hydroxide, leaving 0.5 mmol OH- in 25.0 mL: 0.0200 M. pOH is 1.698970 and pH is 12.301030. Recalculate the limiting equivalent and final volume rather than carrying the earlier acid-excess answer forward. [weak-acid] sqrt(1.8e-5 × 1e-5) = 1.34164e-5 M exceeds C, so the shortcut is impossible. The physical quadratic gives h about 7.15549e-6 M, pH 5.145360 and about 71.55% ionization. Kw/h is about 1.40e-9 M, much smaller than h, so neglecting water is still reasonable here even though ignoring acid depletion is not. [buffer-capacity] OH- consumes HA, leaving 0.00700 mol HA and making 0.01300 mol A-. pH approximately 4.744727 + log10(0.013/0.007) = 5.013573. Both conjugate partners remain appreciable and small equilibrium changes are assumed; neither a negative remainder nor exhaustion may be inserted into this formula. [titration-solubility] If s dissolves, [M2+] = s and [X-] = 2s, so Ksp = s(2s)^2 = 4s^3. Thus s = (4e-12/4)^(1/3) = 1.00e-4 M. A square root assumes a one-to-one dissolution and would fail both the coefficient powers and the particle balance.

Evidence to retain

[acid-base-intro] Science criteria 1, 2 and 3: classify proton transfer, balance atoms/charge, retain molarity-to-amount and final-volume steps, distinguish spectators from excess, and solve the fresh base-excess case. A calculated mixture does not demonstrate a performed titration or an observed endpoint. [weak-acid] Science criteria 1, 2 and 4: retain the equilibrium equation, analytical-versus-free concentration labels, positive quadratic root, depletion check, molecular explanation and water-correction challenge. No calculation establishes safe preparation or actual acid/base handling. [buffer-capacity] Science criteria 1–4: retain neutralization stoichiometry before equilibrium, pKa/ratio calculation, explicit remaining amounts, capacity comparison and the rejected exhausted-buffer shortcut. This reasoning is separate from integration and does not show hands-on solution preparation. [titration-solubility] Criteria 1–4: preserve regime selection, balanced neutralization, all final volumes, endpoint bias and Qsp/Ksp with approximation checks. Criterion 5 may retain repeatability analysis but still needs a separate educator-approved observed titration or formally approved assessment alternative; synthetic endpoints are not performed technique.

Record units, calculations, source/date, uncertainty, and what is measured versus inferred. A simulation or supplied dataset must stay labeled as such. All new cases are paper/data investigations, not laboratory procedures. Any physical exercise requires prior educator and safety approval, an approved protocol, suitable facilities and accessibility provisions. Do not improvise acid/base, electrolysis, gas, high-voltage, combustion, toxic-substance or unknown-substance experiments from these tables. Supplied records do not demonstrate hands-on technique or performed lab hours.