PROJ-CH-0065: Acids & Bases — 酸与碱 完整解答¶
状态: ✅ 已完成 创建日期: 2026-03-14 最后更新: 2026-03-14
Inquiry Question 探究问题¶
How can you identify various chemicals related to a fire at a chemical storage facility?
如何识别化学品仓库火灾后的各种化学品？
Manifest 清单上的化学品¶
在开始答题前，先对清单上的 10 种化学品进行分类：
| Chemical 化学品 | Type 类型 | Electrolyte 电解质 | Expected pH | Physical Form 物理形态 |
|---|---|---|---|---|
| C₆H₁₂O₆ (glucose 葡萄糖) | Molecular 分子化合物 | Non-electrolyte 非电解质 | ~5.5–6 (neutral) | White powdery solid 白色粉末固体 |
| CH₃OH (methanol 甲醇) | Molecular 分子化合物 | Non-electrolyte 非电解质 | ~5.5–6 (neutral) | Flammable liquid 易燃液体 |
| H₂SO₄ (sulphuric acid 硫酸) | Strong acid 强酸 | Strong electrolyte 强电解质 | < 1 | Dense, viscous liquid 浓稠液体 |
| H₂C₂O₄ (oxalic acid 草酸) | Weak acid 弱酸 (Ka₁ = 5.9×10⁻²) | Weak electrolyte 弱电解质 | ~1–3 | White crystalline solid 白色结晶固体，可燃 |
| HCN (hydrocyanic acid 氢氰酸) | Very weak acid 极弱酸 (Ka = 4.9×10⁻¹⁰) | Very weak electrolyte 极弱电解质 | ~4–5 | Flammable liquid 易燃液体 |
| NH₃ (ammonia 氨) | Weak base 弱碱 (Kb = 1.8×10⁻⁵) | Weak electrolyte 弱电解质 | ~8–9 | Sharp odour 刺鼻气味，溶于水 |
| NaOH (sodium hydroxide 氢氧化钠) | Strong base 强碱 | Strong electrolyte 强电解质 | ~13 | White crystalline solid，溶液滑腻 |
| Sr(OH)₂ (strontium hydroxide 氢氧化锶) | Strong base 强碱 (2 OH⁻) | Strong electrolyte 强电解质 | ~13.3 | White crystalline solid，溶液滑腻 |
| CaCl₂ (calcium chloride 氯化钙) | Neutral salt 中性盐 (3 ions) | Strong electrolyte 强电解质 | ~5.5–6 (neutral) | White crystalline solid |
| NaCl (sodium chloride 氯化钠) | Neutral salt 中性盐 (2 ions) | Strong electrolyte 强电解质 | ~5.5–6 (neutral) | White crystalline solid |
Q1¶
If the samples are all either liquids, or white crystalline solids, what tests could we use to begin their identification? (try to list 10 tests)
如果样品都是液体或白色结晶固体，我们可以使用哪些测试来开始识别？（列出 10 种）
Answer 答案:
- pH test (pH 测试) — Use pH paper or a pH meter to measure acidity/basicity of 0.10 M aqueous solutions.
- Electrical conductivity (电导率测试) — Measure how well each 0.10 M solution conducts electricity, indicating ionic content.
- Flame test (焰色反应) — Identify metal ions: Na⁺ gives yellow-orange, Ca²⁺ gives orange-red, Sr²⁺ gives bright red.
- Odour test (气味测试) — Carefully waft to detect characteristic smells (e.g., ammonia has a sharp pungent odour, HCN smells like bitter almonds).
- Physical state and appearance (物理状态和外观) — Note if the original sample is a solid, liquid, powder, or crystalline; note colour, viscosity.
- Solubility in water (水溶性) — All 10 are water-soluble, but rate and heat of dissolution may differ.
- Litmus paper test (石蕊试纸测试) — Quick acid/base classification: red litmus turns blue (base), blue litmus turns red (acid).
- Reaction with metals (与金属反应) — Acids react with active metals (e.g., Zn, Mg) to produce H₂ gas and bubbling.
- Reaction with carbonates (与碳酸盐反应) — Acids react with Na₂CO₃ or NaHCO₃ to produce CO₂ gas (bubbles).
- Density and viscosity measurement (密度和粘度测量) — H₂SO₄ is notably dense (1.84 g/mL) and viscous; methanol is light and low-viscosity.
中文： 可用 pH 测试、电导率、焰色反应、气味测试、物理外观、水溶性、石蕊试纸、与金属反应、与碳酸盐反应、密度/粘度测量等方法来识别化学品。
Q2¶
List all of the 0.10 M species you would expect to conduct electricity well? Explain why.
列出所有预期导电性良好的 0.10 M 溶液，并解释原因。
Answer 答案:
The following species conduct electricity well as 0.10 M solutions:
- H₂SO₄ — Strong acid, fully dissociates: H₂SO₄ → 2H⁺ + SO₄²⁻ (produces many ions)
- NaOH — Strong base, fully dissociates: NaOH → Na⁺ + OH⁻
- Sr(OH)₂ — Strong base, fully dissociates: Sr(OH)₂ → Sr²⁺ + 2OH⁻ (3 ions per formula unit)
- CaCl₂ — Strong electrolyte salt, fully dissociates: CaCl₂ → Ca²⁺ + 2Cl⁻ (3 ions per formula unit)
- NaCl — Strong electrolyte salt, fully dissociates: NaCl → Na⁺ + Cl⁻
Why: Electrical conductivity in solution requires mobile charge carriers (ions). Strong electrolytes fully dissociate into ions, providing many free ions to carry electrical current. The more ions produced per formula unit, the higher the conductivity.
中文： H₂SO₄、NaOH、Sr(OH)₂、CaCl₂、NaCl 导电性良好，因为它们是强电解质，在水中完全电离产生大量自由移动的离子。离子越多，导电性越强。
Q3¶
Why might some samples conduct better than others?
为什么某些样品的导电性比其他的好？
Answer 答案:
Conductivity depends on three factors:
-
Degree of dissociation (电离程度): Strong electrolytes (fully dissociate) conduct much better than weak electrolytes (partially dissociate). Non-electrolytes (molecular compounds like glucose and methanol) hardly conduct at all.
-
Number of ions per formula unit (每个化学式单位产生的离子数): CaCl₂ and Sr(OH)₂ produce 3 ions each, while NaCl and NaOH produce only 2 ions. More ions = higher conductivity.
-
Charge of ions (离子电荷): Ions with higher charges (like Ca²⁺, Sr²⁺) carry more charge per ion, contributing more to conductivity than singly charged ions.
中文： 导电性取决于：① 电离程度（强电解质 > 弱电解质 > 非电解质）；② 每个化学式产生的离子数量（CaCl₂ 产生 3 个离子 > NaCl 产生 2 个）；③ 离子电荷（高价离子携带更多电荷）。
Q4¶
List all of the species that should have low pH?
列出所有应该具有低 pH 的物质。
Answer 答案:
- H₂SO₄ — Strong acid, completely dissociates, pH < 1 at 0.10 M
- H₂C₂O₄ — Moderate weak acid (Ka₁ = 5.9×10⁻²), pH ≈ 1–3 at 0.10 M
- HCN — Very weak acid (Ka = 4.9×10⁻¹⁰), pH ≈ 4–5 at 0.10 M (slightly acidic, but much higher than the above)
中文： H₂SO₄（强酸，pH < 1）、H₂C₂O₄（中等强度弱酸，pH ≈ 1–3）、HCN（极弱酸，pH ≈ 4–5）。其中 H₂SO₄ 的 pH 最低，HCN 的 pH 最接近中性。
Q5¶
List all of the species that should have neutral pH? Explain why.
列出所有应该具有中性 pH 的物质，并解释原因。
Answer 答案:
- C₆H₁₂O₆ (glucose) — Molecular compound, does not ionize in water, produces no H⁺ or OH⁻.
- CH₃OH (methanol) — Molecular compound, does not ionize in water (the OH group is covalently bonded to carbon, not an ionic hydroxide).
- NaCl — Neutral salt formed from a strong acid (HCl) and a strong base (NaOH). Neither Na⁺ nor Cl⁻ undergoes hydrolysis, so the solution is neutral.
- CaCl₂ — Neutral salt formed from a strong acid (HCl) and a strong base (Ca(OH)₂). Neither Ca²⁺ nor Cl⁻ undergoes significant hydrolysis.
Why neutral? Molecular compounds don't produce ions. Salts from strong acid + strong base produce spectator ions that don't react with water, so pH stays near neutral.
中文： C₆H₁₂O₆ 和 CH₃OH 是分子化合物，不电离，不产生 H⁺ 或 OH⁻。NaCl 和 CaCl₂ 是强酸强碱盐，其离子不水解，溶液呈中性。
Q6¶
You notice some solutions are slippery on your fingers. Why might those samples have been slippery?
你注意到一些溶液在手指上感觉滑腻。为什么这些样品会滑腻？
Answer 答案:
The slippery samples are strong bases — NaOH and Sr(OH)₂. They feel slippery because:
- The high concentration of OH⁻ ions reacts with the oils and fats on skin through a process called saponification (皂化反应), converting them into soap-like substances.
- This soap-like layer between your fingers and the solution creates the slippery sensation.
This is why strong bases are sometimes described as feeling "soapy" — they are literally making soap from your skin oils!
⚠️ This is extremely dangerous and should never be done intentionally. Strong bases cause chemical burns.
中文： 滑腻的样品是强碱（NaOH 和 Sr(OH)₂）。OH⁻ 与皮肤上的油脂发生皂化反应，生成类似肥皂的物质，因此感觉滑腻。这非常危险，会造成化学灼伤。
Q7¶
List all of the chemical species from the manifest that you would expect to have high conductivities?
列出清单中预期具有高电导率的所有化学物质。
Answer 答案:
Highest conductivity (strongest electrolytes, most ions):
| Species | Ions produced at 0.10 M | Expected relative conductivity |
|---|---|---|
| Sr(OH)₂ | Sr²⁺ + 2OH⁻ (3 ions, divalent cation) | Very high |
| CaCl₂ | Ca²⁺ + 2Cl⁻ (3 ions, divalent cation) | Very high |
| H₂SO₄ | 2H⁺ + SO₄²⁻ (3 ions, H⁺ has exceptionally high mobility) | Very high |
| NaCl | Na⁺ + Cl⁻ (2 ions) | High |
| NaOH | Na⁺ + OH⁻ (2 ions, OH⁻ has high mobility) | High |
Note: H⁺ and OH⁻ have unusually high ionic mobilities due to the Grotthuss mechanism (proton hopping), so solutions of strong acids and strong bases tend to conduct particularly well.
中文： 预期高电导率的物质为：Sr(OH)₂、CaCl₂、H₂SO₄（产生 3 个离子）> NaCl、NaOH（产生 2 个离子）。H⁺ 和 OH⁻ 具有异常高的离子迁移率。
Q8 — Sample Identification 样品识别¶
Based on the data provided, what is the suggested identity of each sample?
Data Table 数据表¶
| Sample | Conductivity (S/cm) | pH | Other Characteristics |
|---|---|---|---|
| Tap water | 7.5×10⁻⁵ | 6.52 | — |
| Distilled water | 2.7×10⁻⁶ | 5.54 | "Neutral" pH reference |
| 1 | 3.1×10⁻³ | 5.61 | White crystalline solid |
| 2 | 4.9×10⁻³ | 0.98 | Dense, viscous liquid, turns paper black |
| 3 | 3.8×10⁻⁶ | 5.73 | Flammable, low viscosity liquid |
| 4 | 2.9×10⁻³ | 13.21 | White crystalline solid, slippery on skin |
| 5 | 4.7×10⁻³ | 5.62 | White crystalline solid |
| 6 | 4.6×10⁻⁴ | 8.27 | Sharp odour, white crystalline solid |
| 7 | 7.6×10⁻⁴ | 2.91 | Flammable, white crystalline solid |
| 8 | 4.3×10⁻⁵ | 5.70 | Flammable, white powdery solid |
| 9 | 3.8×10⁻⁴ | 4.06 | Flammable, low viscosity liquid |
| 10 | 5.2×10⁻³ | 13.48 | White crystalline solid, slippery on skin |
Answer 答案¶
Identification reasoning — step by step:
Step 1: Identify by extreme pH (最极端的 pH 先确定)¶
Sample 2 → H₂SO₄ (sulphuric acid 硫酸) - pH 0.98 → extremely acidic, only a strong acid gives pH < 1 - Dense, viscous liquid → concentrated H₂SO₄ is famously dense (1.84 g/mL) and viscous - Turns paper black → H₂SO₄ is a powerful dehydrating agent that chars organic materials (removes H₂O from cellulose) - Conductivity 4.9×10⁻³ → very high (strong electrolyte, 3 ions: 2H⁺ + SO₄²⁻)
Step 2: Identify the strong bases (识别强碱)¶
Sample 10 → Sr(OH)₂ (strontium hydroxide 氢氧化锶) - pH 13.48 → highest pH, very basic - Conductivity 5.2×10⁻³ → highest of all samples - Sr(OH)₂ → Sr²⁺ + 2OH⁻ produces 3 ions per formula unit AND 0.20 M OH⁻, giving higher pH and conductivity than NaOH - White crystalline solid, slippery on skin → strong base saponification
Sample 4 → NaOH (sodium hydroxide 氢氧化钠) - pH 13.21 → very basic but lower than Sample 10 - Conductivity 2.9×10⁻³ → high but lower than Sample 10 - NaOH → Na⁺ + OH⁻ produces only 2 ions and 0.10 M OH⁻ (less than Sr(OH)₂) - White crystalline solid, slippery on skin → strong base
Step 3: Identify the weak base (识别弱碱)¶
Sample 6 → NH₃ (ammonia 氨) - pH 8.27 → mildly basic (weak base, only partially ionizes) - Sharp odour → ammonia has a very distinctive pungent/sharp smell — this is the KEY identifier - Conductivity 4.6×10⁻⁴ → moderate (weak electrolyte, partial ionization) - NH₃ + H₂O ⇌ NH₄⁺ + OH⁻ (Kb = 1.8×10⁻⁵)
Step 4: Identify the weak acids (识别弱酸)¶
Sample 7 → H₂C₂O₄ (oxalic acid 草酸) - pH 2.91 → acidic (the most acidic after H₂SO₄) - Flammable, white crystalline solid → oxalic acid is an organic white crystalline solid, flammable - Conductivity 7.6×10⁻⁴ → moderate (weak electrolyte, but Ka₁ = 5.9×10⁻² is relatively large for a weak acid) - H₂C₂O₄ ⇌ H⁺ + HC₂O₄⁻
Sample 9 → HCN (hydrocyanic acid 氢氰酸) - pH 4.06 → mildly acidic - Flammable, low viscosity liquid → HCN is a volatile, flammable liquid (bp 26°C) - Conductivity 3.8×10⁻⁴ → low-moderate (very weak electrolyte, Ka = 4.9×10⁻¹⁰) - The only remaining flammable liquid that is acidic
Step 5: Identify the neutral salts (识别中性盐)¶
Sample 5 → CaCl₂ (calcium chloride 氯化钙) - pH 5.62 → neutral - Conductivity 4.7×10⁻³ → very high (highest among neutral-pH samples) - White crystalline solid - CaCl₂ → Ca²⁺ + 2Cl⁻ produces 3 ions per formula unit, hence highest conductivity among salts
Sample 1 → NaCl (sodium chloride 氯化钠) - pH 5.61 → neutral - Conductivity 3.1×10⁻³ → high but lower than Sample 5 - White crystalline solid - NaCl → Na⁺ + Cl⁻ produces only 2 ions, hence lower conductivity than CaCl₂
Step 6: Identify the non-electrolytes (识别非电解质)¶
Sample 3 → CH₃OH (methanol 甲醇) - pH 5.73 → neutral - Conductivity 3.8×10⁻⁶ → essentially same as distilled water (2.7×10⁻⁶) — non-electrolyte - Flammable, low viscosity liquid → methanol is a classic flammable, light liquid - Molecular compound, does not ionize at all
Sample 8 → C₆H₁₂O₆ (glucose 葡萄糖) - pH 5.70 → neutral - Conductivity 4.3×10⁻⁵ → very low (slightly above distilled water due to trace impurities) - Flammable, white powdery solid → glucose is a white powder - Molecular compound, does not ionize
Final Answer Summary 最终答案汇总¶
| Sample | Identity | Evidence 关键证据 |
|---|---|---|
| 1 | NaCl | Neutral pH (5.61), high conductivity (3.1×10⁻³), white crystalline solid, 2 ions per formula unit |
| 2 | H₂SO₄ | Extremely low pH (0.98), dense viscous liquid, dehydrates paper (turns black), very high conductivity |
| 3 | CH₃OH | Neutral pH (5.73), near-zero conductivity (3.8×10⁻⁶), flammable low-viscosity liquid, non-electrolyte |
| 4 | NaOH | Very high pH (13.21), high conductivity, white crystalline solid, slippery on skin (strong base) |
| 5 | CaCl₂ | Neutral pH (5.62), highest conductivity among neutral samples (4.7×10⁻³), 3 ions per formula unit |
| 6 | NH₃ | Mildly basic pH (8.27), sharp/pungent odour (key identifier), moderate conductivity (weak base) |
| 7 | H₂C₂O₄ | Acidic pH (2.91), flammable white crystalline solid, moderate conductivity (moderate Ka₁) |
| 8 | C₆H₁₂O₆ | Neutral pH (5.70), very low conductivity (4.3×10⁻⁵), flammable white powdery solid, non-electrolyte |
| 9 | HCN | Mildly acidic pH (4.06), flammable low-viscosity liquid, low conductivity (very weak acid) |
| 10 | Sr(OH)₂ | Highest pH (13.48), highest conductivity (5.2×10⁻³), slippery on skin, 3 ions incl. 2 OH⁻ |
Conductivity Ranking 电导率排名¶
| Rank | Sample | Identity | Conductivity | Category |
|---|---|---|---|---|
| 1 | 10 | Sr(OH)₂ | 5.2×10⁻³ | Strong electrolyte (3 ions) |
| 2 | 2 | H₂SO₄ | 4.9×10⁻³ | Strong electrolyte (3 ions, H⁺ high mobility) |
| 3 | 5 | CaCl₂ | 4.7×10⁻³ | Strong electrolyte (3 ions) |
| 4 | 1 | NaCl | 3.1×10⁻³ | Strong electrolyte (2 ions) |
| 5 | 4 | NaOH | 2.9×10⁻³ | Strong electrolyte (2 ions) |
| 6 | 7 | H₂C₂O₄ | 7.6×10⁻⁴ | Weak electrolyte (moderate Ka) |
| 7 | 6 | NH₃ | 4.6×10⁻⁴ | Weak electrolyte (weak base) |
| 8 | 9 | HCN | 3.8×10⁻⁴ | Weak electrolyte (very weak acid) |
| 9 | 8 | C₆H₁₂O₆ | 4.3×10⁻⁵ | Non-electrolyte |
| 10 | 3 | CH₃OH | 3.8×10⁻⁶ | Non-electrolyte |
术语表 | Terminology¶
| English 英文 | Chinese 中文 | Definition 定义 |
|---|---|---|
| Strong Electrolyte | 强电解质 | Substance that fully dissociates into ions in water |
| Weak Electrolyte | 弱电解质 | Substance that partially dissociates into ions in water |
| Non-electrolyte | 非电解质 | Substance that does not produce ions in water |
| Conductivity | 电导率 | Measure of a solution's ability to carry electric current |
| Saponification | 皂化反应 | Reaction of a base with fats/oils to produce soap |
| Dehydrating Agent | 脱水剂 | Substance that removes water from other compounds |
| Hydrolysis | 水解 | Reaction of an ion with water to produce H⁺ or OH⁻ |
| Grotthuss Mechanism | 格罗特斯机制 | Proton hopping mechanism giving H⁺ and OH⁻ high mobility |