酸和碱的浓度
At the end of this lab, students should know...
什么是阿伦尼乌斯酸和碱？
阿伦尼乌斯酸是指在水中溶解时发生解离并产生氢离子的酸，而阿伦尼乌斯碱则是在水中溶解时产生氢氧根离子的碱。
什么是pH，以及如何计算pH？
pH是衡量溶液酸性或碱性强弱的指标。其值等于溶液中氢离子或水合氢离子浓度以10为底的负对数。
如何确定酸和碱的强度？
酸或碱的强度由其在水中解离为共轭离子的能力决定。强酸和强碱在水中完全解离，而弱酸和弱碱则不能完全解离。酸强度可通过解离常数 Ka 来计算，但更常用的是 Ka 的以10为底的负对数，即 pKa。pKa 值越低，酸性越强。
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50 mL 玻璃滴定管5
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60 mL 塑料滴定管，带双阀系统5
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250 mL 锥形瓶15
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10 mL 量筒5
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50 mL 量筒5
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100 mL 烧杯5
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250 mL 烧杯5
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400 mL 烧杯5
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玻璃搅拌棒5
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戒指架5
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中型 2 叉夹5
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滴定管夹5
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1 mL 移液器5
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1 mL 移液器吸头75
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500 mL 带盖聚乙烯瓶5
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掉落计数器5
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pH传感器探头附件5
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pH 7.00 校准缓冲液-1 取决于实验室规模
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pH 10.00 校准缓冲液-1 取决于实验室规模
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手持式数据采集设备5
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闪存驱动器5
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搅拌板5
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搅拌棒5
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NaOH 颗粒30 g
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14.8 M 磷酸1 mL
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酚酞0.1 g
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乙醇5 mL
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KHP20 g
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粉末漏斗3
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150 mL 烧杯1
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125 mL 锥形瓶1
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25 mL 量筒1
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石蜡膜1 卷
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125 mL 聚乙烯瓶2
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1 mL 容量移液管1
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25 mL 容量瓶1
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5 mL 移液器2
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25 mL 锥形瓶1
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抹刀2
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100 mL 烧杯1
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塑料吸管/吸管1
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滴管瓶1
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200 mL 带盖玻璃罐1
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烤箱1
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移液器1
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称量船（至少 10 个）-1 取决于实验室规模
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余额（至少 1）-1 取决于实验室规模
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去离子水-1 取决于实验室规模
来源：美国马里兰州约翰斯·霍普金斯大学 Smaa Koraym
- 试剂的配制
此处展示的是供10名学生（两人一组）实验使用的试剂制备方案，并包含一定余量。请根据实际需要调整用量。
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配制25 mL质量分数为50%的NaOH溶液。称取25 g NaOH颗粒，加入至125 mL锥形瓶中。
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量取25 mL去离子水，并加入该锥形瓶中。
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加入磁力搅拌子，在搅拌器上搅拌溶液直至其外观均匀。混合完成后，用石蜡膜封住瓶口。注意：该溶液在溶解过程中会放热，因此在操作前需使其冷却至室温。
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待溶液冷却后，使用粉末漏斗将其转移至贴有“50% w/w NaOH”标签的聚乙烯瓶中。将溶液储存于腐蚀性化学品专用储存柜中，待后续使用。
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配制25 mL浓度为0.5 M的磷酸溶液。使用1 mL移液管准确量取0.85 mL浓度为14.8 M的浓磷酸原液，加入25 mL容量瓶中。
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用去离子水定容至刻度线。加入磁力搅拌子，搅拌至溶液均匀。
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使用粉末漏斗将溶液转移至贴有“0.5 M H3PO4”标签的聚乙烯瓶中。将溶液储存于腐蚀性化学品专用储存柜中，待后续使用。
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配制5 mL浓度为1%的酚酞溶液。使用移液管将2.5 mL乙醇转移至一个锥形瓶中。
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称取0.05 g酚酞，加入乙醇中。用少量乙醇冲洗称量舟，以转移残留的酚酞。
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加入搅拌子，搅拌至酚酞完全溶解，溶液呈均匀状态。
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向锥形瓶中再加入2.5 mL去离子水，继续搅拌。待溶液充分混匀后，转移至已贴标签的滴瓶中。
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准备干燥的邻苯二甲酸氢钾（KHP）。称取约20 g的KHP原品，放入带盖的玻璃容器中。
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将未加盖的玻璃容器置于125 °F的烘箱中，过夜干燥KHP。
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KHP干燥后，盖紧容器盖子，并将其放置在天平旁冷却至室温。
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确保配备干净且干燥的药匙、若干称量舟，以及一个贴有“过量”标签的150 mL烧杯。
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- 实验室准备
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在每个实验台放置以下玻璃器皿和设备（建议学生两人一组进行实验）：
1 50 mL玻璃滴定管 1 带双阀系统的60 mL塑料滴定管 3 250 mL锥形瓶 1 10 mL量筒 1 50 mL量筒 1 100 mL烧杯 1 250 mL烧杯 1 400 mL烧杯 1 玻璃搅拌棒 1 铁架台 1 中号双夹头夹具 1 滴定管夹 1 1 mL移液枪 15 1 mL移液枪头 1 带盖的500 mL聚乙烯瓶 1 滴数计数器 1 pH传感器探头 1 搅拌器 1 搅拌子 1 数据采集系统 1 U盘
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Q1: How do you prepare a 50% w/w NaOH solution in the laboratory?
Weigh 25 g of NaOH pellets and add them to a 125-mL Erlenmeyer flask. Measure 25 mL of deionized water and add it to the flask. Mix on a stir plate with a magnetic stir bar until homogeneous. The solution generates heat, so allow it to cool before transferring to a labeled polyethylene bottle for storage in a corrosive storage cabinet.
Q2: What is the procedure for diluting stock phosphoric acid to 0.5 M concentration?
Use a 1-mL volumetric pipette to measure 0.85 mL of stock 14.8 M phosphoric acid and add it to a 25-mL volumetric flask. Fill the flask with deionized water to the volume marking. Mix with a magnetic stir bar until homogeneous, then transfer to a labeled polyethylene bottle and store in a corrosive storage cabinet.
Q3: How is phenolphthalein indicator solution prepared for titration experiments?
Transfer 2.5 mL of ethanol into an Erlenmeyer flask and add 0.05 g of phenolphthalein. Stir until dissolved, then rinse the weigh boat with ethanol to transfer residual phenolphthalein. Add 2.5 mL of deionized water and mix until homogeneous. Transfer the solution to a labeled dropper bottle for use.
Q4: Why is potassium hydrogen phthalate dried before use in acid-base titrations?
Potassium hydrogen phthalate (KHP) is dried overnight in an oven at 125 °F to remove moisture that could affect the accuracy of titration calculations. Dry KHP serves as a reliable primary standard for standardizing base solutions. Once dried, the container is sealed and cooled at room temperature before use.
Q5: What glassware and equipment are essential for each student pair in an acid-base titration lab?
Each station requires a 50-mL glass burette, 60-mL plastic burette, three 250-mL Erlenmeyer flasks, graduated cylinders, beakers of various sizes, a glass stirring rod, ring stand with clamps, pipettes, a pH sensor probe, stir plate with magnetic stir bar, and a data acquisition system to record measurements.
Q6: How should corrosive reagents like NaOH and phosphoric acid be stored after preparation?
Both NaOH and phosphoric acid solutions must be transferred to labeled polyethylene bottles and stored in a corrosive storage cabinet. Polyethylene containers resist chemical degradation from strong acids and bases, preventing leaks and contamination. Proper labeling ensures safe identification and prevents accidental misuse.
Q7: What precautions should be taken when preparing concentrated NaOH solutions?
When dissolving NaOH pellets in water, the reaction is highly exothermic and produces significant heat. Cover the flask with paraffin film during mixing and allow the solution to cool completely before handling or transferring. This prevents burns and ensures safe handling of the caustic reagent.