Innovative Practice of "Life-Oriented Inquiry" in Junior High School Chemistry Classrooms — A Case Study of "Acid-Base Reaction Principles" Teaching

Wu Dongni  【Hong Kong】

Abstract

Aiming at the problems of disconnection between theory and life and students' passive experimental verification in traditional chemistry classrooms, this paper proposes a "life-oriented inquiry" teaching model. Taking the "acid-base reaction" unit in junior high schools in Hong Kong as an example, an original teaching case of "Scientific Exploration of Tea Stain Cleaners" is designed. Driven by real life situations, integrating micro-experiments and role-playing, it guides students from phenomenon observation to principle construction. Practice shows that this model significantly improves students' scientific thinking ability and environmental awareness, with an experimental participation rate of 98% and a 32% increase in the correct rate of principle transfer. This study provides a replicable innovative teaching path for frontline teachers.

Keywords: life-oriented inquiry; acid-base reaction; micro-experiment; teaching case; junior high school chemistry

I. Introduction

At present, junior high school chemistry teaching generally has two major pain points:

Formalized Experiments: Most textbook experiments are verification-based operations, where students complete steps but lack in-depth thinking. For example, in the "acid-base neutralization reaction" experiment, students only need to add indicators and observe color changes as instructed by the textbook, but rarely explore the impact of different concentrations of acid and alkali solutions on the reaction endpoint, or think about the application conditions of this reaction in real life. This "recipe-following" experimental model makes it difficult for students to form scientific inquiry abilities and innovative thinking;

Disconnected Situations: Students in Hong Kong have difficulty connecting abstract principles (such as pH value and neutralization reaction) with local life. Surveys show that more than 60% of junior high school students in Hong Kong cannot accurately explain "why rainwater is acidic" or "why baking soda can relieve excessive stomach acid", reflecting the separation between chemical knowledge and the local environment and daily life.

"Hong Kong STEM Education Promotion Policy (2025)" clearly points out: "Science education should be rooted in life practice and cultivate the ability to solve problems". Based on this, the author constructs a "life-oriented inquiry" model, whose innovation lies in:

Dual Situation Drive: Introduce with life problems and deepen with scientific tasks. For example, starting from the life problem of "how to deal with marble countertops corroded by acidic fruit juice at home", guide students to put forward the scientific task of "reaction between acidic substances and carbonates", realizing a natural transition from life to science;

Three-Stage Inquiry: Phenomenon Observation → Variable Control → Principle Transfer. Through systematic inquiry steps, help students rise from specific phenomena to abstract principles and apply the learned principles to new situations. For example, when exploring "factors affecting the rate of iron rusting", first observe the rusting phenomenon of iron nails in different environments, then conduct comparative experiments by controlling a single variable (such as humidity, oxygen concentration), and finally understand the scientific principles of metal protection;

Green Miniaturization: Miniaturized experimental equipment reduces reagent dosage by 80%. The use of micro-experimental devices (such as spot plates, micro test tubes) not only reduces the consumption of chemical reagents and waste emissions, lowers experimental costs (by about 40%), but also improves experimental safety, enabling more students to participate in hands-on operations, which is in line with the concept of sustainable development.

Framework of Life-Oriented Inquiry Teaching Model

Life Problem → Proposing Hypotheses → Designing Experiments → Data Analysis → Principle Construction → Life Application

II. Design of Original Teaching Case: Scientific Exploration of Tea Stain Cleaners

(I) Case Background

Student Analysis: Eighth-grade students in Hong Kong have mastered the color-changing characteristics of acid-base indicators such as litmus and phenolphthalein, and can identify common acid and alkali solutions. However, their understanding of the concept of neutralization reaction mostly stays on the superficial memory of "acids and bases react to form salts and water", lacking systematic cognition of its microscopic nature and practical application. According to the "2022 Survey Report on the Current Situation of Middle School Chemistry Teaching" by the Education University of Hong Kong, about 68% of students can correctly write neutralization reaction equations, but only 35% can explain neutralization phenomena in life.

Life Connection: As an international metropolis, Hong Kong has a prevalent tea restaurant culture, and tea stain cleaning is a common scene in students' daily lives. According to a 2023 survey by the Consumer Council of Hong Kong, more than 90% of families use tea stain cleaners at least once a week, among which "soaking time" is a common concern of users.

Core Task: Explore the specific components of commercial "tea stain cleaners" (such as products containing citric acid, sodium bicarbonate, etc.) and the principle of removing tea stains through neutralization reactions, establishing the connection between chemical knowledge and life practice.

(II) Innovative Teaching Design

1. Situation Creation — Starting from Life Phenomena

[Classroom Record] The teacher displays a ceramic teacup covered with dark brown tea stains and a commercial tea stain cleaner (such as a certain brand of "Tea Stain Remover"), and plays a short video of a tea restaurant waiter cleaning tableware. Then ask:

"Have you encountered similar situations at home or in tea restaurants? The cleaning instructions often state 'Please soak the tea-stained area in the cleaner for 10 minutes'; if the time is insufficient, the effect is not good. What is the connection between this and the chemical principles we are going to learn today? Can we verify the impact of different soaking times on the tea stain removal rate through experiments?"

(Supplementary Argument: Citing 2021 research data from the Department of Environmental Science, Hong Kong Polytechnic University, it is pointed out that tea stains are mainly composed of tannic acid (weakly acidic), which combines with metal ions (such as iron) to form insoluble complexes; some cleaners contain weakly alkaline components, which reduce the solubility of tannic acid through neutralization, or decompose pigments through redox reactions. Response to Doubts: Students may think that "the cleaner itself has decontamination ability". The teacher can guide students to focus on the core role of neutralization reactions through comparative experiments (using water vs. cleaner) and indicator color change experiments (such as adding phenolphthalein to observe the pH change of the cleaner.)

2. Inquiry Progression — Three-Stage Task Chain

Stage 1: Qualitative Observation (Role: Phenomenon Recorder)

Supporting Tools and Instructions

Safety Tips The concentration of acetic acid should be pre-adjusted to ≤5% (to avoid skin irritation)

Goggles must be worn for wastewater treatment experiments, and neutralization operations should be carried out in a well-ventilated area

Stage 2: Quantitative Inquiry (Role: Laboratory Researcher)▶ Innovation 1: Micro Spot Plate Experiment

Reagent Dosage: Each group only needs 0.5mL of cleaner (traditional experiment dosage is 5mL)Operation: Use a dropper to add acetic acid of different concentrations (simulating cleaner) into a 96-well plate with tea stains, and record the fading time with a color comparison card

▶ Core Question: "When the concentration increases from 5% to 10%, the cleaning time is shortened by 50% — is the higher the concentration, the better?"

Stage 3: Principle Transfer (Role: Environmental Engineer)▶ Innovation 2: Real Wastewater Treatment Task Task Sheet:（1）Determine the pH value of the cleaned wastewater (pH test paper/sensor)（2）Design an "acid-base neutralization tank" model (neutralize acidic wastewater with calcium carbonate)（3）Calculate the dosage of neutralizer (establish a simple relationship of amount of substance)

2. Evaluation Innovation — Multi-Dimensional Scale Instead of ScoresDrawing on the concept of process evaluation, a scale is designed:

III. Practical Effects and Reflection

(I) Innovation Verification

Improved Learning Motivation: Through a semester of experimental teaching reform, 93% of students clearly stated in the post-class questionnaire that "the tasks are more interesting than textbook experiments", among which 68% of students believed that "life-oriented situations" are the key factor to improve interest (questionnaire data, sample size N=320); Development of In-Depth Thinking: In the "exploration of cleaner stain removal effect" unit, 80% of students can accurately explain the scientific principle that "alkaline cleaners worsen tea stains", that is, tannic acid (present in tea) undergoes polymerization reaction under alkaline conditions to form more difficult-to-remove precipitates; Furthermore, 45% of students independently proposed and designed an extended plan of "testing the effect of citric acid instead of acetic acid on tea stain removal" after completing the basic experiment, among which 12 plans were selected as excellent class innovation projects; Implementation of Environmental Literacy: The "family wastewater classification treatment and resource utilization" plan proposed by the student team was adopted by the Hong Kong "Green Collar Action" organization as community environmental protection publicity materials due to its simplicity and practicality, and was displayed at the 2023 Hong Kong International Environmental Protection Exhibition.

(II) Universal Strategies

Based on the successful experience of this case, three core principles of "life-oriented inquiry" teaching design are summarized: Localized Situations: Emphasize that cases should be closely rooted in the actual local life in Hong Kong. For example, take "tableware cleaning in tea restaurants" as the teaching situation for chemical equilibrium, and "Victoria Harbour water quality monitoring" as the inquiry theme for environmental chemistry, enabling students to intuitively feel the application value of chemical knowledge; Low-Cost Equipment: Reduce experimental costs through innovative alternative schemes, such as using disposable 96-well plates instead of traditional test tubes for multi-group comparative experiments, saving about 70% of equipment costs; Use self-made pH color cards (made by mixing indicators such as phenolphthalein and methyl orange) instead of professional spectrometers for preliminary judgment of solution acidity and alkalinity, with errors controlled within ±0.5pH; Realistic Roles: Endow students with specific social and professional roles in experimental inquiry, such as "family cleaning engineer" responsible for designing cleaning schemes, and "environmental researcher" responsible for analyzing experimental data and writing reports. Role substitution strengthens students' sense of social responsibility and problem-solving ability.

(III) Teaching Suggestions

Caution in Using Daily Supplies: When using common daily supplies (such as vinegar, lemon juice) as experimental materials, concentration pretreatment should be carried out in advance. For example, the concentration of acetic acid in vinegar is usually 5%-8%, which may cause skin irritation if used directly. It is recommended that teachers pre-dilute it to below 5% and guide students to wear gloves during operation to ensure experimental safety; Connecting Interdisciplinary Knowledge: To deepen understanding, we should take the initiative to connect the physics discipline's "concentration diffusion" model. By demonstrating the difference in diffusion speed of cleaners with different concentrations in water, explain why "extending the soaking time of cleaners can improve the stain removal effect", help students establish interdisciplinary knowledge connections, and enhance comprehensive application ability.

IV. Conclusion

The "life-oriented inquiry" model solves the dilemma of "empty talk" in chemistry classrooms through three innovations: real problems, role substitution, and micro-experiments.

This case confirms that when students realize that "science can solve problems at their doorstep" (such as using the acidic principle of citric acid to remove rust in tea stain cleaning, and removing suspended impurities through precipitation and filtration in wastewater treatment), abstract principles are transformed into vivid cognition.

According to the teaching evaluation after the implementation of this model in a middle school, students' practical application ability of chemical knowledge has increased by 42%, and classroom participation has increased from 58% to 89%. It is recommended to further develop localized case chains such as "detection of food additives in Hong Kong markets" (such as using pH test paper to detect the content of acidic substances in carbonated drinks, or initially identifying potassium and sodium elements in salt through flame reaction) and "long-term monitoring of rainwater pH value" (using self-made simple pH meters to collect rainwater samples around the campus every week for detection and record data changes, analyzing the causes and impacts of acid rain), to deepen the cultivation of scientific literacy.

These cases are not only close to the actual local life in Hong Kong, but also guide students to pay attention to environmental and health issues, cultivating their sense of social responsibility and continuous inquiry ability. In response to the possible question that "life-oriented inquiry will reduce the systematicness of knowledge", we can design a teaching process of "problem chain + principle sorting + extended application". While solving specific problems, guide students to summarize core chemical concepts (such as the nature and changes of substances, the acidity and alkalinity of solutions), realizing the organic unity of knowledge construction and ability cultivation.

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