# Some Gases - Grade 10 (SEE) Science
## Complete Chapter Notes with All Exercises - NEB Curriculum
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## 🎯 Chapter Overview
**Gases are all around us, playing vital roles in our environment and industries.** This chapter, "Some Gases," focuses on two incredibly important gases: **Ammonia ($NH_3$)** and **Carbon Dioxide ($CO_2$)**. These detailed notes will guide you through their laboratory preparation, properties, and everyday uses in a simple and memorable way.
**This is a fundamental chemistry chapter with a strong presence in the SEE exam, especially the diagram-based questions.** We will break down each step of the lab preparations, explain the chemistry behind their properties, and solve every single exercise from your textbook. By the end, you'll be an expert on these essential gases.
**Weightage:** 8-10 marks in SEE examination
**Time Required:** 15-20 periods
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## 📚 Learning Objectives
After studying this chapter, you will be able to:
- Describe the laboratory preparation of Carbon Dioxide and Ammonia gas with labeled diagrams.
- Explain the principles and chemical reactions involved in their preparation.
- List the physical and chemical properties of both gases.
- Identify and test for Carbon Dioxide and Ammonia.
- State the conditions required for the industrial manufacture of Ammonia by Haber's Process.
- Explain the various uses of Carbon Dioxide and Ammonia in daily life and industries.
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## ⚫ Part A: Carbon Dioxide ($CO_2$)
Carbon Dioxide is a crucial gas for life on Earth, used by plants for photosynthesis. It's also a major greenhouse gas.

### 1. Laboratory Preparation of Carbon Dioxide

**Principle:** Carbon dioxide is prepared in the lab by the reaction of a metallic carbonate (usually Calcium Carbonate, $CaCO_3$) with a dilute mineral acid (like Hydrochloric Acid, HCl).

**Chemical Reaction:**
Calcium Carbonate + Hydrochloric Acid $\rightarrow$ Calcium Chloride + Water + Carbon Dioxide
$CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2 \uparrow$

**Procedure:**
1.  Marble chips or limestone pieces ($CaCO_3$) are placed in a Woulfe's bottle.
2.  A thistle funnel and a delivery tube are fitted into its two mouths. The thistle funnel must be dipped below the acid level to prevent the gas from escaping through it.
3.  Dilute HCl is poured into the bottle through the thistle funnel.
4.  A brisk effervescence occurs, and $CO_2$ gas is produced.
5.  The gas is collected in a gas jar by the **upward displacement of air**.



[Image of the laboratory preparation of Carbon Dioxide gas]


**Collection Method:** $CO_2$ is collected by **upward displacement of air** because it is about 1.5 times **heavier than air**. It cannot be collected over water as it is fairly soluble in it.

### 2. Physical and Chemical Properties of $CO_2$

**Physical Properties:**
- It is a **colorless** and **odorless** gas.
- It is **heavier than air**.
- It is fairly soluble in water.
- It can be easily liquefied and solidified. Solid $CO_2$ is called **Dry Ice**.

**Chemical Properties:**
- **Nature:** It is **acidic** in nature. It dissolves in water to form carbonic acid ($H_2CO_3$), which turns moist blue litmus paper red.
  $CO_2 + H_2O \rightarrow H_2CO_3$ (Carbonic Acid)
- **Combustibility:** It is **non-combustible** and a **non-supporter of combustion**. This is why it's used in fire extinguishers.
- **Reaction with Lime Water:**
  - **Short Time:** When passed through lime water ($Ca(OH)_2$) for a short time, it turns milky due to the formation of insoluble Calcium Carbonate.
    $Ca(OH)_2 + CO_2 \rightarrow CaCO_3 \downarrow + H_2O$
  - **Long Time:** If excess $CO_2$ is passed, the milkiness disappears due to the formation of soluble Calcium Bicarbonate.
    $CaCO_3 + H_2O + CO_2 \rightarrow Ca(HCO_3)_2$ (Soluble)
- **Reaction with Magnesium:** Although a non-supporter of burning, a burning magnesium ribbon continues to burn in a jar of $CO_2$ because the heat from Mg is enough to decompose $CO_2$.
  $2Mg + CO_2 \rightarrow 2MgO + C$

### 3. Uses of Carbon Dioxide
- **Photosynthesis:** Plants use $CO_2$ to make their food.
- **Fire Extinguishers:** Used to put out fires.
- **Soft Drinks:** To make carbonated beverages (soda, cola).
- **Dry Ice:** Used as a refrigerant to keep things cold (like ice cream).
- **Manufacturing:** Used to manufacture washing soda and urea.

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## ⚪ Part B: Ammonia ($NH_3$)
Ammonia is a colorless gas with a characteristic pungent smell. It is a vital industrial chemical, primarily used to make fertilizers.

### 1. Laboratory Preparation of Ammonia

**Principle:** Ammonia is prepared in the lab by heating an ammonium salt (like Ammonium Chloride, $NH_4Cl$) with a strong alkali (like Calcium Hydroxide, $Ca(OH)_2$).

**Chemical Reaction:**
Ammonium Chloride + Calcium Hydroxide $\xrightarrow{Heat}$ Calcium Chloride + Water + Ammonia
$2NH_4Cl + Ca(OH)_2 \xrightarrow{Heat} CaCl_2 + 2H_2O + 2NH_3 \uparrow$

**Procedure & Setup:**
1.  A mixture of $NH_4Cl$ and $Ca(OH)_2$ is taken in a hard glass test tube.
2.  The test tube is clamped in a slanted position with its **mouth tilted downwards**. This is crucial to prevent the water vapor produced from condensing and trickling back, which could crack the hot test tube.
3.  The gas produced is passed through a **drying tower** containing **Quicklime (CaO)** to remove moisture.
4.  The dry gas is collected in an inverted gas jar by the **downward displacement of air**.



[Image of the laboratory preparation of Ammonia gas]


**Drying & Collection:**
- **Drying Agent:** Only **Quicklime (CaO)** is used. Other agents like conc. $H_2SO_4$ (acid) or anhydrous $CaCl_2$ cannot be used because they react with ammonia (base).
- **Collection Method:** Ammonia is collected by **downward displacement of air** because it is **lighter than air**. It cannot be collected over water because it is **highly soluble in water**.

### 2. Industrial Manufacture: Haber's Process
Ammonia is manufactured on a large scale by the direct combination of Nitrogen and Hydrogen.

**Reaction:** $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) + Heat$

**Necessary Conditions for Maximum Yield:**
- **High Pressure:** 200 - 900 atmospheres.
- **Optimal Temperature:** 450°C - 500°C.
- **Catalyst:** Finely divided **Iron (Fe)**.
- **Promoter:** Traces of **Molybdenum (Mo)** to increase the efficiency of the catalyst.

### 3. Properties and Uses of Ammonia

**Physical Properties:**
- It is a **colorless** gas with a **strong, pungent smell**.
- It is **lighter than air**.
- It is **highly soluble in water**. A concentrated aqueous solution of ammonia is called **Liquor Ammonia** ($NH_4OH$).
- It is non-combustible.

**Chemical Properties:**
- **Nature:** It is **basic** in nature. It turns moist red litmus paper blue and phenolphthalein solution pink.
- **Reaction with Acids:** Being a base, it reacts with acids to form ammonium salts.
  - $NH_3 + HCl \rightarrow NH_4Cl$ (Ammonium Chloride)
  - $2NH_3 + H_2SO_4 \rightarrow (NH_4)_2SO_4$ (Ammonium Sulphate)

**Uses of Ammonia:**
- **Fertilizers:** Used to manufacture nitrogenous fertilizers like Urea and Ammonium Sulphate.
- **Refrigerant:** Used as a coolant in ice plants and refrigerators.
- **Cleaning Agent:** Its solution is used to remove grease and stains.
- **Industrial Chemicals:** Used to make nitric acid, washing soda, and explosives.

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## 📋 4. COMPLETE EXERCISE SOLUTIONS

### **1. Give Reasons:**
**a. Ammonia gas is collected by the downward displacement of air.**
**Answer:** Because ammonia is **lighter than air**, so it rises and fills the gas jar from top to bottom, pushing the heavier air downwards and out. Also, it cannot be collected over water because it is **highly soluble** in it.

**b. Concentrated $H_2SO_4$ is not used to dry ammonia gas.**
**Answer:** Because ammonia ($NH_3$) is a basic gas and concentrated sulphuric acid ($H_2SO_4$) is an acid. They react with each other to form ammonium sulphate.
$2NH_3 + H_2SO_4 \rightarrow (NH_4)_2SO_4$

**c. Carbon dioxide is used in fire extinguishers.**
**Answer:** Because carbon dioxide is a **non-combustible gas** and a **non-supporter of combustion**. Being heavier than air, it displaces oxygen and cuts off the oxygen supply to the fire, thus extinguishing it.

**d. The mouth of the test tube is tilted downwards during the lab preparation of ammonia.**
**Answer:** Water is produced as a byproduct in the reaction. Tilting the test tube downwards allows this water vapor to flow out of the tube. This prevents it from condensing, trickling back onto the hot glass, and **cracking the test tube**.

**e. A burning magnesium ribbon continues to burn in a jar of $CO_2$.**
**Answer:** The intense heat from the burning magnesium is sufficient to break down the carbon dioxide molecule into carbon and oxygen. The oxygen released then supports the continued burning of the magnesium.
$2Mg + CO_2 \rightarrow 2MgO + C$

### **2. Answer the following questions:**
**a. What is Dry Ice? What is its use?**
**Answer:** Dry ice is the solid form of carbon dioxide ($CO_2$), which forms at -78°C. It is used as a **refrigerant** for preserving food and in theatrical productions to create fog effects.

**b. What happens when $CO_2$ is passed through lime water for a long time? Give a balanced equation.**
**Answer:** First, the lime water turns milky due to the formation of insoluble calcium carbonate. When excess $CO_2$ is passed for a long time, the milkiness disappears due to the formation of water-soluble calcium bicarbonate.
**Equation:** $CaCO_3 + H_2O + CO_2 \rightarrow Ca(HCO_3)_2$

**c. What is liquor ammonia? Name the compound formed in a gas jar of ammonia if the jar is moist.**
**Answer:** Liquor ammonia is a concentrated aqueous solution of ammonia. If the gas jar is moist, ammonia gas will react with water ($H_2O$) to form **Ammonium Hydroxide ($NH_4OH$)**.
**Equation:** $NH_3 + H_2O \rightarrow NH_4OH$

### **3. Diagrammatic Questions:**
**Study the given figure for the lab preparation of $CO_2$ and answer:**

**i. Find the mistake in the apparatus.**
**Ans:** The thistle funnel is too short; its end must be **dipped inside the acid** to prevent the gas from escaping through it.
**ii. What happens if quicklime is replaced by Conc. $H_2SO_4$ in the drying tower for ammonia prep?**
**Ans:** Ammonia gas will react with the sulphuric acid to form ammonium sulphate. Therefore, the ammonia gas will not be collected.
**Equation:** $2NH_3 + H_2SO_4 \rightarrow (NH_4)_2SO_4$

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## ✅ 5. CHAPTER CHECKLIST & EXAM TIPS
**Exam Hotspots 🔥:**
-   **Lab Prep Diagrams:** The labeled diagrams for both $CO_2$ and $NH_3$ preparation are extremely important. Practice drawing them.
-   **Give Reasons:** Questions about collection methods, drying agents, and the tilted test tube are very frequently asked.
-   **Haber's Process:** Memorize the five necessary conditions for the industrial production of ammonia.
-   **Lime Water Test:** Be prepared to write both reactions (for a short time and a long time).

**Your Pre-Exam Checklist:**
- [ ] I can draw and label the lab preparation for both $CO_2$ and $NH_3$.
- [ ] I can explain why $CO_2$ is collected by upward displacement of air.
- [ ] I can explain why $NH_3$ is collected by downward displacement of air.
- [ ] I can list all the conditions for Haber's process.
- [ ] I can write the balanced equations for the lime water test.
- [ ] I know the main uses of both gases.
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## 🎊 CONCLUSION
Carbon Dioxide and Ammonia are two gases with contrasting properties but equal importance in our world. From the fizz in your soda to the fertilizer that grows your food, their chemistry is at work all around us. Mastering their preparation and properties is a key step in understanding practical chemistry.
**Key to Success:** Practice the Diagrams + Master the 'Give Reasons' + Memorize the Reactions = Excellent Marks!