课程思政背景下分析化学辩证元素探索及教学实践

doi:10.3866/PKU.DXHX202001020

Abstract

Abstract:

In the university, analytical chemistry is an important basic course for junior college students. There is a variety of dialectical views, rules, and relationships of materialism in analytical chemistry. Fully excavating these dialectical elements and infiltrating them into the classroom teaching process is necessary. This will not only help students deeply understand the subject knowledge, but also cultivate their dialectical thinking mode, establish the correct worldview and scientific methodology. This is conducive to the same resonance frequency between knowledge education and thinking education, and fits the current course ideological and political education. In the present paper, combining many years of teaching practice, the author briefly explains the integration of dialectical elements in analytical chemistry with the corresponding teaching content.

Key words: Analytical chemistry, Dialectics, Course ideology and politics, Classroom teaching

MSC2000:

Yunqing Duan, Zhiqing Duan. Exploration and Teaching Practice of Dialectics in Analytical Chemistry under the Background of Course Ideology and Politics[J].University Chemistry, 2020, 35(12): 150-157.

Figures/Tables 5

序号	实践中的问题	理论解答	理论知识联系
1	标定时基准物质的选择及称取质量有何要求？	H₂C₂O₄与KHP皆可用来标定NaOH浓度，但采用后者时称量误差更小。根据所配NaOH的近似浓度以及液体用量不少于20 mL (以20–30 mL为宜)，计算需称量的KHP质量	基准物质测量误差的减免基准物质质量计算
2	为何不用直接滴定方式？	因为NH₄⁺的酸性太弱(cK_a < 10⁻⁸)，故不能直接滴定，而用置换滴定方式，将其转化成能被准确定滴定的强酸	弱酸准确滴定判据的应用滴定方式的拓展应用
3	滴定时选用何种指示剂？	化学计量点时，溶液为六次甲基四胺的水溶液，pH约为9.0，选用酚酞(8.0–9.6)作为指示剂。与标定实验所用指示剂相同，体现标定和测定尽量选用同一指示剂，以降低实验过程中CO₂的影响，减小实验误差	酸碱溶液pH计算指示剂的选择误差减免CO₂影响
4	铵盐试样中若存在游离酸对测定有何影响？若需预先中和，选用何种指示剂？中和所用V_NaOH是否需要准确计量？	铵盐中的游离酸会使V_NaOH增大，产生正误差，故需预先中和。由于滴定终点时为铵盐溶液，pH约为5.1，故选用甲基红(4.2–6.2)指示终点。中和所用V_NaOH需要准确计量，并在结果中予以扣除	误差分析酸碱溶液pH计算指示剂的选择原则误差减免
5	甲醛中的游离酸对测定有何影响？中和时，选用何种指示剂？中和所用V_NaOH是否要准确计量？	甲醛中的游离酸也会使V_NaOH增大而产生正误差，须预先进行中和。因为中和后的甲醛要加入试液中，故中和时宜选用酚酞指示终点(与测定时的指示剂相同，以免干扰滴定终点的颜色判断)。中和所用V_NaOH不需准确计量	误差分析分析以降低系统不确定度为目的误差减免
6	甲醛用量是否需要准确计量？	相对于铵盐，甲醛须过量，故不需准确计量。但是，若标定的c_NaOH偏高，则可适当加大试样取样量，同时，甲醛也应作相应调整，保证过量	滴定分析对化学反应的要求之一——定量联系实际

知识点	知识内容描述	蕴含的辩证关系
EDTA的性质	常用的胺羧配合剂，本身是四元酸，水中溶解度小。在酸性溶液中还可接受两个质子，成为六元酸，故溶液中有7种型体，只有Y⁴⁻能与M有效配合	普遍联系
EDTA与M配合的特点	配位能力强：有6个可供配位的原子；稳定性强：能形成5个五元环结构；M无色则MY无色，M有色则MY同色	普遍性
	广泛性：能与几乎所有金属离子相配合，要选择适宜实验条件提高选择性	对立统一事物的两面性
	绝大多数配位比为1 : 1，个别除外，如Mo : Y = 2 : 1	普遍性与特殊性
配位平衡	动态平衡副反应酸效应系数与分布系数	绝对与相对事物的两面性事物的普遍联系
滴定过程中溶液颜色变化	MIn + Y = MY + In (指示剂变色原理) 开始时溶液呈现MIn的颜色，终点时为指示剂In的颜色；若金属离子有色，则终点前后分别为MIn + M及In + MY(M)的混合色	现象与本质
指示剂的封闭与僵化	若K_f(MIn) > K_f(MY)，置换反应不发生，指示剂封闭；若K_f(MIn)只是略小于K_f(MY)，则发生指示剂僵化现象	原因与结果现象与本质
滴定过程	滴定前半段pM逐渐增大，在计量点附近pM发生骤然跃升，形成突跃，颜色发生变化	量变与质变
pH范围	由于Y的酸效应，须使用缓冲溶液稳定溶液的pH；适宜pH范围既要考虑M允许的最低pH (对于易水解的金属离子，还要考虑允许的最高pH)，又要综合指示剂的适宜pH，具体要通过试验确定	理论联系实际
准确滴定M的判据	lg(cK_f’) > 6 若溶液pH高于M允许滴定的最低pH，可准确定滴定M；若低于该pH，则不能准确滴定；酸效应曲线	可能性与现实性理论联系实际
提高滴定选择性	合理应用其他胺羧配合剂与金属离子形成配合物稳定性的差异提高滴定选择性。如用EDTA滴定Cu²⁺时Zn²⁺、Cd²⁺、Mn²⁺有干扰，而EDTP可以选择性滴定Cu²⁺，此时Zn²⁺、Cd²⁺、Mn²⁺不产生干扰^[6]	普遍性与特殊性普遍联系、永恒发展
选择性滴定的判据	要准确滴定M (E_r = ±0.1%)，则要求ΔlgK_f + lg(c_M/c_N) ≥ 6。若c_M = c_N，则ΔlgK_f = lgK_f(MY) − lgK_f(NY) ≥ 6；若c_M = 10c_N，则lgK_f(MY) − lgK_f(NY) ≥ 5即可。而准确度的要求不同，对判别式的要求也就不同。如若E_r = ±0.3%，则选择性滴定判据就变成ΔlgK_f + lg(c_M/c_N) ≥ 5	绝对与相对原因与结果

滴定法	滴定基本反应	平衡常数及影响	共性与个性的体现
酸碱滴定	H⁺ + OH⁻ = H₂O (强强互滴) H⁺ + A⁻ = HA (强酸滴弱碱) OH⁻ + HA = A⁻ + H₂O (强碱滴弱酸)	酸(碱)的K_a (K_b)越大，酸(碱)性越强，突跃范围越大	除沉淀滴定(个性)外，其他皆与平衡常数呈正相关(共性)
配位滴定	M + Y = MY	配合物的K_f越大，突跃范围越大
氧化还原滴定	n₂O₁ + n₁R₂ = n₂R₁ + n₁O₂	反应的平衡常数K越大，反应完全程度越高，突跃范围越大
沉淀滴定	Ag⁺ + X⁻ = AgX	沉淀的K_sp越大，突跃范围越小

授课时间	授课专业	授课方式	上课人数	不同得分率人数(占上课人数的比例)					成绩直方图
授课时间	授课专业	授课方式	上课人数	90%−100%	80%−89%	70%−79%	60%−69%	0−59%	成绩直方图
2019–2020 学年秋季学期	公共农科专业	多元素融合授课	134	37 (27.6%)	45 (33.6%)	32 (23.9%)	15 (11.2%)	5 (3.7%)
	公共农科专业	对照	139	25 (18.8%)	48 (34.8%)	34 (24.6%)	18 (13.0%)	12 (8.7%)
	应用化学专业	多元素融合授课	69	13 (18.9%)	22 (31.9%)	18 (26.1%)	12 (17.4%)	4 (4.3%)

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Exploration and Teaching Practice of Dialectics in Analytical Chemistry under the Background of Course Ideology and Politics

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