Questions and Answers
What is the common name of the compound CaOCl2?
Bleaching powder
Name the substance which on treatment with chlorine yields bleaching powder.
Calcium hydroxide
Name the sodium compound which is used for softening hard water.
Sodium carbonate
What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
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Write an equation to show the reaction between Plaster of Paris and water.
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Compounds such as alcohols and glucose contain hydrogen but are not categorised as acids. Why is this?
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Why does distilled water not conduct electricity, whereas rainwater does?
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Why do acids not show acidic behaviour in the absence of water?
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Five solutions A, B, C, D, and E exhibit pH values of 4, 1, 11, 7, and 9, respectively. Which solution is neutral?
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Which type of medicine is used for treating indigestion?
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What is water of crystallisation?
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What happens to the color of copper sulphate when heated?
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Match the following compounds with their uses:
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Which of the following would you suggest as a remedy for acidity: lemon juice, vinegar or baking soda solution?
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What taste do acids have?
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What color does blue litmus paper turn in the presence of an acid?
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What is the effect of bases on red litmus paper?
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What is litmus solution extracted from?
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Litmus solution appears __________ when it is neutral.
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What happens to a fabric stained with curry when washed with a basic substance?
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What gas is usually released when an acid reacts with a metal?
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Which of these can be used as olfactory indicators based on the activities tested?
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What happens when sodium carbonate reacts with hydrochloric acid?
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Acid + Metal → __________ + Hydrogen gas.
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What is the general reaction for neutralization?
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What should not be kept in brass or copper vessels?
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What indicates that a compound is acidic during the conductivity test?
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Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
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Why does an aqueous solution of an acid conduct electricity?
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Why does dry HCl gas not change the colour of the dry litmus paper?
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While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
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How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?
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How is the concentration of hydroxide ions (OH–) affected when excess base is dissolved in a solution of sodium hydroxide?
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Which solution has more hydrogen ion concentration: solution A with pH 6 or solution B with pH 8?
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Do basic solutions also have H+ ions? If yes, then why are these basic?
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Under what soil condition do you think a farmer would treat the soil of his fields with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
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What is the process of dissolving an acid or a base in water called?
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Which acid is produced by the stomach to aid digestion?
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Which of the following is a strong acid?
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What is the pH of a neutral solution?
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Study Notes
Acids, Bases, and Indicators
Acids taste sour and turn blue litmus paper red; bases taste bitter and turn red litmus paper blue.
Natural indicators include litmus (derived from lichen), turmeric, and synthetic indicators such as methyl orange and phenolphthalein.
Turmeric stain turns reddish-brown when exposed to a base and turns yellow in neutral or acidic conditions.
The color of litmus solution is purple when neutral; it changes with acidity or basicity.
Characteristics of Acids and Bases
Acids and bases neutralize each other, forming salts and water in a reaction.
Common laboratory acids: hydrochloric acid (HCl), sulfuric acid (H₂SO₄), nitric acid (HNO₃), and acetic acid (CH₃COOH).
Common laboratory bases: sodium hydroxide (NaOH), calcium hydroxide (Ca(OH)₂), potassium hydroxide (KOH), magnesium hydroxide (Mg(OH)₂).
Reactions of Acids and Bases with Metals
When metals react with acids, hydrogen gas is liberated, forming a salt (e.g., Zn + H₂SO₄ → ZnSO₄ + H₂).
The general reaction for metal and acid: Acid + Metal → Salt + Hydrogen gas.
Activity involving zinc granules in acid evolves hydrogen gas, which can be tested with a burning candle (will ignite).
Reactions of Metal Carbonates and Hydrogencarbonates with Acids
Metal carbonates (e.g., Na₂CO₃) and metal hydrogencarbonates (e.g., NaHCO₃) react with acids, producing carbon dioxide, water, and salt.
The reactions yield a gas that can turn lime water milky (indicating CO₂ presence).
Neutralization Reactions
The neutralization reaction can be summarized as: Base + Acid → Salt + Water.
An example reaction is NaOH + HCl → NaCl + H₂O, where phenolphthalein changes color to indicate pH.
Reactions of Metallic Oxides with Acids
Metallic oxides react with acids to form salts and water, similar to base reactions, e.g., Copper oxide + HCl → Copper(II) chloride + Water.
Non-metallic Oxides with Bases
Carbon dioxide reacts with calcium hydroxide (limewater) to produce a salt and water, indicating non-metallic oxides can behave as acids.
Properties Common to All Acids and Bases
All acids generate hydrogen ions (H⁺) in solution, while bases generate hydroxide ions (OH⁻).
Solutions of acids conduct electricity (due to ionization), while sugars and alcohols do not conduct electricity.
Acid-Base Reactions in Water
The presence of water is essential for acids and bases to produce ions (e.g., HCl + H₂O → H₃O⁺ + Cl⁻).
Bases dissolve in water, yielding hydroxide ions; not all bases are alkalis (which are soluble in water).
Safety and Exothermic Reactions
Dissolving acids and bases in water is exothermic; concentrated acids should always be added to water slowly to avoid splashing and potential burns.
A procedure involving concentrated H₂SO₄ and water demonstrates this exothermic reaction, which can cause temperature increases.
Observations and Experimental Activities
Document color changes of indicators in acid/base reactions.
Conduct tests to identify acid/base properties using olfactory indicators (e.g., onion or vanilla essence) and observe changes in odor.
Perform additional activities involving reactions with metals and carbonates to deepen understanding of acid-base chemistry concepts.### Acid-Base Characteristics
Acids like HCl and HNO3 exhibit acidic properties in aqueous solutions due to the presence of hydronium ions (H3O+).
Compounds such as alcohol and glucose do not show acidic properties as they do not dissociate to release H3O+ in solution.
Dilution Process
Mixing an acid or base with water leads to dilution, reducing ion concentration (H3O+/OH–).
Dilution is crucial for safe handling and utilization of concentrated acids or bases.
Electrical Conductivity
Aqueous solutions of acids can conduct electricity due to the dissociation into ions that facilitate the flow of electric current.
Dry HCl and Litmus Paper
Dry HCl gas does not change the color of dry litmus paper as it requires a solvent (water) to ionize and demonstrate acidic properties.
Acid Dilution Protocol
When diluting an acid, it is essential to add acid to water to prevent exothermic reactions that can lead to splattering of concentrated acid.
Ion Concentration Changes
Diluting an acid decreases the concentration of hydronium ions (H3O+), making the solution less acidic.
Adding excess base to a sodium hydroxide solution increases the concentration of hydroxide ions (OH–).
pH Scale and Measurement
The pH scale ranges from 0 (very acidic) to 14 (very alkaline), with a neutral pH of 7.
Universal indicators are employed to visually represent pH levels through color changes, indicative of ion concentration.
Acids and Bases Strength
Strong acids release a greater number of H+ ions compared to weak acids, defining their strength.
Similarly, strong bases release more OH– ions than weak bases.
pH Sensitivity in Life
Living organisms function optimally within a narrow pH range (7.0 to 7.8).
Acid rain (pH < 5.6) negatively impacts aquatic ecosystems by lowering river water pH.
Tooth Decay Risk
Tooth decay risks arise when mouth pH falls below 5.5, as lower pH levels corrode tooth enamel.
Neutralization Reactions
Antacids, often basic substances, neutralize excess stomach acid to alleviate indigestion.
Natural Acids and Their Sources
Common natural acids include acetic acid (vinegar), citric acid (orange, lemon), and lactic acid (sour milk).
Family of Salts
Salts are categorized based on their ions; salts with similar positive or negative radicals form families (e.g., NaCl with Na2SO4).
pH of Salts
Salts derived from strong acids and strong bases are neutral (pH = 7).
Salts from strong acids and weak bases are acidic (pH < 7), while those from strong bases and weak acids are basic (pH > 7).
Chlor-Alkali Process
Sodium chloride reacts in an electrolysis process to produce sodium hydroxide (NaOH), chlorine gas (Cl2), and hydrogen gas (H2).
This process is fundamental in producing several everyday chemicals, highlighting the importance of common salt.
Uses of Important Chemicals
Bleaching Powder: Produced from chlorine and slaked lime; used for bleaching and purifying water.
Baking Soda (Sodium Bicarbonate): Utilized in cooking and as an antacid; neutralizes excess stomach acid.
Washing Soda: Derived from sodium carbonate; used in various industries and to soften water.
Water of Crystallization
Many salts contain fixed water molecules within their structure, known as water of crystallization, affecting their characteristics and behavior when heated.
Example: Copper sulfate (CuSO4·5H2O) changes color when heated, indicating the loss of water of crystallization.
Plaster of Paris
Formed from heating gypsum, it is used in construction and arts, showcasing the importance of hydrated salts in various applications.### Plaster of Paris
Plaster of Paris is a white powder made from calcium sulfate hemihydrate (CaSO₄·1/2H₂O).
When mixed with water, it hardens into gypsum (CaSO₄·2H₂O) through a reaction:
CaSO₄·1/2H₂O + H₂O → CaSO₄·2H₂O
The term "half a water molecule" refers to the sharing of water in the structure of calcium sulfate.
Uses of Plaster of Paris
Commonly used in medicine for immobilizing fractured bones.
Employed in crafting toys and decorative materials.
Utilized to create smooth surfaces in construction.
Acid-Base Chemistry
Acid-base indicators are dyes that signal the presence of acids and bases.
Acids release H⁺ ions in an aqueous solution, while bases release OH⁻ ions.
Reactions between acids and metals produce hydrogen gas and salts.
Reaction of acids with carbonates produces salts, water, and carbon dioxide.
pH Scale
The pH scale ranges from 0 (strongly acidic) to 14 (strongly alkaline), with 7 being neutral.
Optimal pH is essential for metabolism in living organisms.
A neutral solution has a pH of exactly 7; solutions with lower pH are acidic and those with higher pH are basic.
Electrical Conductivity
Acidic and basic solutions conduct electricity due to the ions they release in water.
Neutralization Reactions
Acids and bases neutralize each other, forming salts and water.
Example reactions include:
Strong acid + base → salt + water
Water of Crystallization
Refers to fixed numbers of water molecules in a salt's formula unit.
Distilled Water vs Rain Water
Distilled water does not conduct electricity because it lacks ions, while rainwater contains dissolved minerals that make it conductive.
Storage of Plaster of Paris
Must be stored in a moisture-proof container to prevent premature hardening due to water absorption.
Experimental Activities
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Prepare Natural Indicators:
- Use beetroot or other natural materials for pH testing.
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Soda-Acid Fire Extinguisher:
- Combine sodium hydrogencarbonate with dilute sulfuric acid to release carbon dioxide, demonstrating a practical application of acid-base reactions.
Questions for Review
- Common name of CaOCl₂ is bleaching powder.
- Sodium carbonate used for softening hard water.
- Heating sodium bicarbonate releases carbon dioxide.
- Reaction of Plaster of Paris with water can be represented with a chemical equation.
Practical Applications
- Important uses of washing soda and baking soda in household cleaning and cooking.
Studying That Suits You
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Description
Test your understanding of acids, bases, and salts with this quiz on Chapter 2. Explore concepts such as taste, remedies for acidity, and properties of substances. Perfect for reinforcing key ideas in chemistry.
