Class 11 Chemistry Notes Chapter 7 (Chapter 7) – Lab Manual (English) Book
Detailed Notes with MCQs of Chapter 7 from your Chemistry Lab Manual, which deals with Systematic Qualitative Analysis of Inorganic Salts. This is a crucial topic, not just for your practical exams, but also because questions based on the reactions, colours, and principles involved frequently appear in various government examinations.
Objective: To identify the cation (basic radical) and the anion (acidic radical) present in an unknown inorganic salt using systematic chemical analysis.
I. Basic Concepts
- Inorganic Salt: Composed of a positively charged ion (cation/basic radical, usually a metal ion or NH₄⁺) and a negatively charged ion (anion/acidic radical, derived from an acid).
- Qualitative Analysis: Determining the identity (quality) of the constituents, not the amount (quantity).
- Systematic Procedure: Analysis is done step-by-step, first for the anion and then for the cation, often involving preliminary tests followed by specific group analysis and confirmatory tests.
II. Preliminary Tests
These tests give preliminary clues about the nature of the salt but are not conclusive.
- Physical Examination (Colour and Appearance):
- Colour: Can suggest the presence of certain ions (e.g., Blue: Cu²⁺, Light Green: Fe²⁺, Dark Green: Ni²⁺, Pink: Co²⁺, Mn²⁺ (light pink), Brown: Fe³⁺, Yellow/Brownish-yellow: Fe³⁺). White salts usually indicate absence of these transition metal ions.
- Appearance: Crystalline or amorphous. Hygroscopic (absorbs moisture), Deliquescent (absorbs moisture and dissolves), Efflorescent (loses water of crystallization).
- Dry Heating Test: Heating a small amount of salt in a dry test tube. Observe changes like:
- Gas Evolution: Colourless, odourless (CO₂ from carbonates), Colourless with odour (NH₃ from ammonium salts, SO₂ pungent smell from sulfites), Coloured gas (NO₂ reddish-brown from nitrates, Br₂ reddish-brown from bromides, I₂ violet from iodides).
- Sublimation: White sublimate (Ammonium salts, HgCl₂), Grey sublimate (Hg), Violet sublimate (Iodine).
- Colour Change on Heating/Cooling: Zn salts (Yellow when hot, white when cold), Pb salts (Yellow/Buff when hot and cold).
- Decrepitation: Crackling sound (NaCl, Pb(NO₃)₂).
- Melting/Fusion: Alkali metal salts often fuse.
- Flame Test: Making a paste of the salt with conc. HCl on a clean platinum wire loop and introducing it to a non-luminous Bunsen flame. Characteristic colours indicate certain cations:
- Crimson Red: Strontium (Sr²⁺)
- Apple Green: Barium (Ba²⁺)
- Brick Red: Calcium (Ca²⁺)
- Golden Yellow: Sodium (Na⁺) (persistent)
- Lilac/Pale Violet: Potassium (K⁺) (viewed through blue glass)
- Green with Blue Centre: Copper (Cu²⁺)
- Note: Conc. HCl converts salts to more volatile chlorides.
- Borax Bead Test: Heating borax (Na₂B₄O₇·10H₂O) on a platinum loop forms a colourless glassy bead (Na₂B₄O₇ → 2NaBO₂ + B₂O₃). Touching the hot bead with a speck of salt and reheating in oxidizing (outer) and reducing (inner) flames gives coloured beads for certain transition metals (e.g., Cu: Blue in oxidizing, Red/opaque in reducing; Co: Blue in both; Ni: Brown/Violet in oxidizing, Grey in reducing; Fe: Yellow/Brown in oxidizing, Green in reducing; Mn: Violet/Pink in oxidizing, Colourless in reducing).
- Charcoal Cavity Test: Mixing salt with Na₂CO₃ and heating in a charcoal cavity using a blowpipe (reducing flame). Observe residue/incrustation:
- Yellow (hot & cold): Pb salts (residue: grey bead, incrustation: yellow)
- Yellow (hot), White (cold): Zn salts (incrustation)
- White: Ba, Sr, Ca, Mg, Al salts (infusible white residue)
- Metallic beads/scales: Ag (white bead), Cu (red scales), Pb (grey bead).
- Cobalt Nitrate Test: Used for salts leaving a white residue in the charcoal cavity test (Mg, Al, Zn). Moisten the residue with Co(NO₃)₂ solution and heat strongly.
- Pink Mass: Magnesium (Mg²⁺)
- Blue Mass: Aluminium (Al²⁺)
- Green Mass: Zinc (Zn²⁺)
III. Analysis of Anions (Acidic Radicals)
Performed by treating the salt/solution with dilute H₂SO₄, then concentrated H₂SO₄, followed by specific tests for anions not detected in the first two groups.
Group I: Anions detected by Dilute H₂SO₄ (React with dil. H₂SO₄ to evolve specific gases)
- Reagent: Dilute H₂SO₄
- Anions: CO₃²⁻, S²⁻, SO₃²⁻, NO₂⁻
- Procedure: Add dil. H₂SO₄ to a small amount of salt. Observe gas evolution (warm if necessary).
| Anion | Observation with Dil. H₂SO₄ | Confirmatory Test |
|---|---|---|
| CO₃²⁻ | Brisk effervescence, colourless, odourless gas (CO₂). | Gas turns lime water (Ca(OH)₂) milky (CaCO₃ ppt). Milky appearance disappears on passing excess gas (Ca(HCO₃)₂ formation - soluble). |
| S²⁻ | Colourless gas with rotten egg smell (H₂S). | Gas turns lead acetate paper black (PbS ppt). Gas turns sodium nitroprusside solution purple/violet. |
| SO₃²⁻ | Colourless gas with pungent smell like burning sulphur (SO₂). | Gas turns acidified K₂Cr₂O₇ paper green (Cr³⁺ formation). Gas decolourises acidified KMnO₄ solution. |
| NO₂⁻ | Brown fumes (NO₂) evolve (may need warming). Initially NO (colourless) forms, reacts with air O₂ to give brown NO₂. | Add KI solution and starch solution to salt solution, then acidify -> Blue/Black colour (I₂ liberated). Add FeSO₄ solution -> Brown ring test (less distinct than for NO₃⁻). |
Group II: Anions detected by Concentrated H₂SO₄ (React with conc. H₂SO₄, often on heating, to evolve characteristic gases)
- Reagent: Concentrated H₂SO₄
- Anions: Cl⁻, Br⁻, I⁻, NO₃⁻, CH₃COO⁻, C₂O₄²⁻ (Oxalate)
- Procedure: Add conc. H₂SO₄ to a small amount of salt. Observe gas evolution (warm if necessary).
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Q: The _________ is a large, leaf-shaped piece of cartilage that blocks the opening to the larynx during swallowing.
A: epiglottis
Q
A: ...
Q: The _________ is also known as the voice box because it contains the vocal cords.
A: larynx
Q: The _________ is located anterior to the esophagus and carries air to the bronchi.
A: trachea
Q: The ___________ is the largest cartilage of the larynx and the thyroid gland is located anterior to it.
A: thyroid cartilage
Q
A: ...
Q: The pharynx is also known as the throat.
A: True
Q: Which of the following is not a function of the respiratory system?
A: Regulation of blood pH
B. Producing vocal sounds
C. Filtration of air
D. Transport of gases
Q: The nasal cavity helps to warm and humidify the air breathed in through the nose.
A: True
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A: ...
Q: The trachea is located posterior to the esophagus.
A: False
Q: The bronchioles are the smallest airways in the respiratory system.
A: False
Q: The larynx is also known as the voice box because it contains the vocal cords.
A: True
Q: The epiglottis is a large, leaf-shaped piece of cartilage that blocks the opening to the larynx during swallowing.
A: True
Q: The lungs are the main organs of the respiratory system.
A: True
Q: The right lung has three lobes, while the left lung has two lobes.
A: True
Q: The alveoli are tiny air sacs in the lungs where gas exchange takes place.
A: True
Q: The diaphragm is a muscle located below the lungs that helps with breathing.
A: True
Q: The pleura is a thin membrane that lines the lungs and chest cavity.
A: True
Q: The respiratory system is responsible for taking in oxygen and removing carbon dioxide from the body.
A: True
Q: The trachea is also known as the windpipe.
A: True
Q: The bronchi are the main passageways that carry air into the lungs.
A: True
Q: The alveoli are surrounded by capillaries, which are tiny blood vessels.
A: True
Q: The exchange of gases between the air in the alveoli and the blood in the capillaries is called external respiration.
A: True
Q: The exchange of gases between the blood and the cells of the body is called internal respiration.
A: True
Q: The diaphragm contracts and flattens during inhalation, increasing the volume of the chest cavity.
A: True
Q: The diaphragm relaxes and moves upward during exhalation, decreasing the volume of the chest cavity.
A: True
Q: The intercostal muscles, located between the ribs, also help with breathing.
A: True
Q: The respiratory system is closely linked to the circulatory system, as oxygen is transported by the blood to the body's tissues.
A: True
Q: The respiratory system is controlled by the respiratory center in the brainstem.
A: True
Q: The respiratory rate is the number of breaths taken per minute.
A: True
Q: The average respiratory rate for an adult at rest is 12-20 breaths per minute.
A: True
Q: Factors such as exercise, stress, and illness can affect the respiratory rate.
A: True
Q: Common respiratory conditions include asthma, bronchitis, pneumonia, and emphysema.
A: True
Q: Smoking is a major risk factor for many respiratory diseases, including lung cancer.
A: True
Q: Allergies can trigger respiratory symptoms such as sneezing, coughing, and wheezing.
A: True
Q: Air pollution can also have negative effects on respiratory health.
A: True
Q: Regular exercise can help improve lung capacity and overall respiratory function.
A: True
Q: Deep breathing exercises can help reduce stress and promote relaxation.
A: True
Q: The respiratory system plays a role in maintaining the body's pH balance by regulating carbon dioxide levels.
A: True
Q: Sneezing and coughing are protective reflexes that help clear the airways of irritants.
A: True
Q: The sense of smell is closely linked to the respiratory system, as odor molecules are detected by receptors in the nasal cavity.
A: True
Q: The respiratory system works in coordination with the cardiovascular system to deliver oxygen to the body's tissues and remove carbon dioxide.
A: True