【PEP Edition】Grade 9 Chemistry (Vol. 2): Chemistry at the Table — Life Activities and the Six Essential Nutrients

Enter the Micro Chemistry Lab: Your Dining Table

Welcome to the opening of this course! Have you ever realized that every meal is actually a complexexchange of chemical substances? To sustain life, we need to obtain six essential nutrients from food:proteins, carbohydrates, fats, vitamins, minerals, and water.

From a chemical perspective, the first four are generally complexorganic compounds, while water and minerals are inorganic substances. These materials are not only the "building blocks" of the body (like proteins) but also the "fuel" that powers the engine of life (like carbohydrates and fats).

Core Experiment: From Seawater to Table Salt

Among all mineral salts, table salt (sodium chloride) is the most typical. Therefined salton our tables is obtained by purifyingcrude salt. This is not just a physical separation, but a process of removing harmful impurities. We evaluate the experimental results by calculating the yield of refined salt:

Core Formula: $Refined\ Salt\ Yield = \frac{Mass\ of\ Refined\ Salt}{Mass\ of\ Crude\ Salt} \times 100\%$

Common Mistakes

Stirring:During evaporation, continuously stir with a glass rod to prevent localized overheating that may cause splattering.
Residual Heat:When a significant amount of solid appears in the evaporating dish, stop heating and let the residual heat dry it completely.
Safety:After heating, place the evaporating dish on a wire gauze to cool; do not place it directly on the lab bench.

QUESTION 1

Among the six essential nutrients, which two are generally not classified as organic compounds?

Proteins and carbohydrates

Fats and vitamins

Minerals and water

Carbohydrates and minerals

QUESTION 2

Regarding the crude salt purification experiment, which of the following operations is correct?

During filtration, the liquid level should be above the edge of the filter paper

During evaporation, keep heating until all water has completely disappeared

The evaporating dish can be placed directly on a platform balance for weighing

When a significant amount of solid appears in the evaporating dish, stop heating and let residual heat dry it

QUESTION 3

Hemoglobin has a relative molecular mass of approximately 68,000. What substance is it primarily responsible for transporting in the human body?

Glucose

Oxygen

Amino acids

Minerals

QUESTION 4

Which nutrient deficiency can lead to night blindness in humans?

Vitamin A

Vitamin C

Vitamin D

Proteins

QUESTION 5

What is the main physiological function of fats in the human body?

Basic life substance and repair material

Primary and direct energy source for the body

Maintaining vision and regulating metabolism

Reserve energy source and maintaining body temperature

Comprehensive Inquiry: Food Labels and Lab Skills

Analyzing Chemicals at the Dining Table

A student bought a bag of soda crackers. The ingredient list includes: wheat flour, white sugar, refined vegetable oil, fresh eggs, milk powder, and salt. The student then conducted a simulated purification experiment on the salt in the lab.

1. [Short Answer] What properties of sodium chloride are utilized by the method used in this experiment? Considering the source of crude salt, determine whether the purified salt is a pure substance, and design an experiment to verify your conclusion.

Answer:
Sample Answer: (1) Properties utilized: Sodium chloride is readily soluble in water, its solubility is only slightly affected by temperature, it is stable, and does not easily decompose when heated. (2) Purity: The purified salt is not a pure substance, as it may still contain soluble impurities such as calcium chloride and magnesium chloride. (3) Verification experiment: Dissolve a small amount of the purified salt in water, and add a sodium carbonate solution. If a white precipitate forms, it indicates the presence of calcium ions (impurities), proving the salt is not pure.

2. [Fill in the blanks] Proteins are extremely complex compounds composed of many ______. Hemoglobin binding with ______ can lead to carbon monoxide poisoning. Carbohydrates are compounds made up of the three elements ______, ______, and ______. The main carbohydrate found in rice and flour is ______, which is converted by the catalytic action of ______ in the human digestive system into ______ (chemical formula $C_6H_{12}O_6$).

Answer:
Sample Answer: amino acids; carbon monoxide (CO); carbon, hydrogen, oxygen (C, H, O); starch; enzymes; glucose.

3. [Short Answer] Conduct a group debate on the topic "Pros and Cons of Using Plastics."

Answer:
Sample Answer: [Pros] Low cost, lightweight, and corrosion-resistant; widely used in food packaging, medical devices, and aerospace materials, greatly improving our quality of life. [Cons] Waste plastics are difficult to decompose; long-term accumulation damages soil structure and harms marine life; incineration releases harmful gases, contributing to "white pollution." [Conclusion] We should reduce the use of single-use plastics, actively sort and recycle, and develop new biodegradable polymer materials.