Shanghai Edition Junior High School English Grade 9 Part 1: Chemical Labels in Daily Life: Understanding Acids, Bases, and Salts

Welcome to chemistry’s 'seasoning cabinet' and 'cleaning station'! From the tangy lemon to the slippery detergent, chemical 'labels' are everywhere in our daily lives.

1. Scientific Definition: Identifying Common Properties of Substances

Scientific Definition: Scientists discovered that despite their different uses, substances like tomato juice, vinegar, and even liquid from car batteries all contain a special class of compounds—acids. These substances exhibit similar chemical characteristics when dissolved in water.

2. Laboratory Observation: Physical 'Business Cards' of Acids and Bases

In the lab, we identify these substances through careful observation:

Acid Group (Concentrated Hydrochloric Acid, Concentrated Sulfuric Acid, Concentrated Nitric Acid): Observe color and state. When you open the reagent bottle cap, concentrated hydrochloric acid and nitric acid often producewhite fumes, due to their volatility.
Base Group (Sodium Hydroxide, Calcium Hydroxide, Ammonia Water): Solid sodium hydroxide (NaOH) has strong hygroscopic properties and absorbs moisture from the air, leading todeliquescence. Meanwhile, ammonia water emits a pungent, irritating odor.

3. Identification Tool: The Magic of Indicators

To safely identify acids and bases, we no longer taste them—we useindicators. By adding small amounts of solution to a spot plate and dropping in purple litmus or colorless phenolphthalein, we can observe remarkable color changes—clear visual evidence of a substance's chemical nature.

Safety Red Line

Never touch strong acids or bases directly during experiments! Sodium hydroxide is highly corrosive—if it contacts your skin, immediately rinse with plenty of water and follow your teacher’s instructions for further treatment.

QUESTION 1

Consult resources or product manuals to find out which household items contain acids?

Vinegar, lemon juice, car lead-acid batteries, carbonated drinks

Table salt, baking soda, dish soap, tap water

QUESTION 2

Tomato juice is acidic. Predict two observable properties of tomato juice.

1. Turns purple litmus blue; 2. Reacts with copper metal to produce bubbles

1. Turns purple litmus red; 2. May produce bubbles when reacting with zinc granules

QUESTION 3

In the kitchen, there are table salt (NaCl) and baking soda (Na₂CO₃) — two white solids. How can you distinguish them using only common kitchen items?

Take samples and add vinegar separately. The one producing bubbles is baking soda; the one showing no change is salt.

Take samples and add cold water separately. The one dissolving faster is baking soda; the slower one is salt.

QUESTION 4

Which of the following statements about dilute acids reacting with metals is correct?

Dilute acids can react with all metals to produce hydrogen gas

Dilute acids can react with reactive metals like magnesium, zinc, and iron, but not with copper or silver

QUESTION 5

Lime (main component: calcium hydroxide) is commonly used as a building material. What chemical property is being utilized?

Reacting with carbon dioxide to form hard calcium carbonate

Easily decomposes into calcium oxide when heated