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Questions and Answers
How can you identify the contents of each test tube using only red litmus paper?
By dipping the red litmus paper into the solutions; if it turns blue, the solution is basic, if it remains red, the solution is acidic.
Why should curd and sour substances not be kept in brass and copper vessels?
They react with the metal, leading to the formation of harmful compounds.
Write a balanced chemical equation for the reaction of hydrochloric acid with sodium carbonate, if one of the compounds formed is calcium chloride.
Na2CO3 + 2 HCl → 2 NaCl + H2O + CO2
Which gas is usually liberated when an acid reacts with a metal?
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The reaction of an acid with a base can be summarized as: Base + Acid → ______ + ______.
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What color does phenolphthalein turn in the presence of a base?
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All acids produce hydroxide ions in water.
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What happens to copper oxide when it reacts with dilute hydrochloric acid?
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Which of the following is a common indicator used to test for acids and bases?
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What do bases generate in water?
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What is the common name of the compound CaOCl2?
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Name the substance which on treatment with chlorine yields bleaching powder.
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Name the sodium compound which is used for softening hard water.
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What will happen if a solution of sodium hydrogencarbonate 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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What is water of crystallisation?
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Which of the following types of medicines is used for treating indigestion?
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A neutral solution has a pH of exactly 7.
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What happens when dilute hydrochloric acid reacts with magnesium ribbon?
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Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9 respectively. Which solution is neutral?
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What happens to the pH of fresh milk as it turns into curd?
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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 color of 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: A (pH 6) or B (pH 8)?
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What effect does the concentration of H+(aq) ions have on the nature of the solution?
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Do basic solutions also have H+(aq) ions? If yes, then why are these basic?
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Under what soil conditions would a farmer treat the soil with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
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Which of the following acids is formed from vinegar?
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What is the salt formed by the combination of hydrochloric acid and sodium hydroxide?
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What chemical is commonly used as a remedy for excess stomach acid?
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Match the following naturally occurring acids with their natural sources:
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Study Notes
Acids, Bases, and Salts
- Acids contribute a sour taste, and bases contribute a bitter taste in foods.
- Lemon juice and baking soda can help alleviate acidity due to their neutralizing properties.
- Acids turn blue litmus red; bases turn red litmus blue.
- Indicators such as litmus, turmeric, methyl orange, and phenolphthalein are used to test for acidity or basicity.
Natural Indicators
- Litmus, derived from lichen, is purple in neutral solutions but changes color in the presence of acids or bases.
- Other natural indicators include red cabbage, turmeric, and flower petals.
Chemical Properties of Acids and Bases
- Common acids in labs include hydrochloric acid (HCl), sulfuric acid (H₂SO₄), and acetic acid (CH₃COOH).
- Testing involves observing color changes with indicators in acidic and basic environments.
- Olfactory indicators change odor in acidic or basic conditions, demonstrated with onion and vanilla essence in experiments.
Reactions of Acids and Bases
- Metals react with acids to displace hydrogen, producing hydrogen gas and a salt:
Acid + Metal → Salt + Hydrogen gas - Example: Zinc reacts with sulfuric acid, producing hydrogen gas observable by bubbles and testing with a burning candle.
Metal Carbonates and Acids
- Metal carbonates react with acids to produce a salt, water, and carbon dioxide: Metal carbonate/Metal hydrogencarbonate + Acid → Salt + Carbon dioxide + Water
- Passing CO₂ through lime water results in a white precipitate due to calcium carbonate formation.
Neutralization Reactions
- Acids and bases neutralize each other to form a salt and water: Base + Acid → Salt + Water
- Example: Sodium hydroxide and hydrochloric acid react to form sodium chloride and water.
Metallic Oxides and Acids
- Metallic oxides react with acids similarly to bases, producing a salt and water: Metal oxide + Acid → Salt + Water
- Copper oxide dissolves in hydrochloric acid, leading to a blue-green solution of copper(II) chloride.
Non-Metallic Oxides and Bases
- Non-metallic oxides (like CO₂) react with bases (like lime water) to form salts and water, indicating their acidic nature.
Characteristics of Acids
- Acids produce hydrogen ions (H⁺) in solution, influencing their chemical behavior and electrical conductivity.
- Not all hydrogen-containing compounds are acidic; only those producing H⁺ ions in solution are classified as acids.
Behavior of Acids and Bases in Water
- Acids dissolve in water to release H⁺ ions, while bases furnish hydroxide (OH⁻) ions, leading to electrical conductivity.
- Mixing concentrated acids with water is highly exothermic; always add acid to water, never the reverse, to prevent splashing or container breakage.
Safety Precautions
- Concentrated acids should be handled with care, utilizing appropriate protective measures.
Summary of Key Reactions
- Summary of common reactions involving acids, bases, metals, and carbonates for quick reference.
- Practice writing balanced chemical equations for various acid-base reactions as part of studying these reactions comprehensively.### Dilution and Ion Concentration
- Diluting an acid or base with water decreases the concentration of ions (H3O+/OH–) per unit volume.
- The process of adding water to an acid or base is called dilution.
Acidic Character in Solutions
- Compounds like HCl and HNO3 show acidic characteristics in aqueous solutions due to their ionization to produce H+ ions.
- Compounds like alcohol and glucose do not exhibit acidic behavior in water because they do not dissociate to release H+ ions.
Conductivity of Acidic Solutions
- Aqueous solutions of acids conduct electricity due to the presence of free-moving ions, primarily H+ ions.
Behavior of HCl Gas
- Dry HCl gas does not change the color of dry litmus paper because it does not release ions until it is dissolved in water.
Dilution Recommendations
- When diluting an acid, it is safer to add acid to water to avoid violent reactions due to exothermic heat and splashing.
Effect of Dilution on H3O+ Concentration
- The concentration of hydronium ions (H3O+) decreases when an acid solution is diluted.
Impact of Excess Base on OH– Concentration
- Adding excess base to a sodium hydroxide solution increases the concentration of hydroxide ions (OH–).
pH Scale and Indicator
- pH scale ranges from 0 (very acidic) to 14 (very alkaline), with 7 being neutral.
- Universal indicators show varying colors based on hydrogen ion concentration, aiding in identifying acidic or basic substances.
Strength of Acids and Bases
- Strong acids produce more H+ ions compared to weak acids at the same concentration, while strong bases yield more OH– ions compared to weak bases.
Importance of pH in Daily Life
- Most living organisms function optimally within a pH range of 7.0 to 7.8.
- Acid rain, with a pH below 5.6, can harm aquatic ecosystems by lowering river water pH.
Role of pH in the Digestive System
- The stomach produces hydrochloric acid for digestion, which operates effectively at the body's natural pH range.
- Antacids, which are bases, help neutralize excess stomach acid during indigestion.
Tooth Decay and pH
- Tooth decay begins when the mouth's pH drops below 5.5, corroding tooth enamel, which is essential for dental health.
Chemical Warfare in Nature
- Bee stings and stinging nettles inject acid that causes pain; mild bases can alleviate these effects and counteract acid.
Salts and Their Classification
- Salts are formed from the reaction of acids and bases, and they can be classified based on their acidic or basic nature.
- Neutral salts form from strong acids and bases, while salts derived from weak bases or acids are either acidic or basic.
Properties of Common Salts
- Sodium chloride is a neutral salt obtained from hydrochloric acid and sodium hydroxide.
- Common salt serves as a raw material for various chemical products, such as sodium hydroxide, baking soda, and bleaching powder.
Chlor-Alkali Process
- Passing electricity through brine (aqueous sodium chloride) produces sodium hydroxide, chlorine, and hydrogen gases.
Uses of Bleaching Powder
- Bleaching powder is produced from the reaction of chlorine with dry slaked lime and is used in textile, paper industries, and for disinfecting water.
Baking Soda Functions
- Sodium hydrogencarbonate (baking soda) is useful as an antacid and in cooking, releasing carbon dioxide when heated, which helps in leavening.
Washing Soda Applications
- Sodium carbonate (washing soda) is utilized in glass, soap, and chemical manufacturing, as well as in treating hard water.
Water of Crystallization
- Many salts, like copper sulfate, contain water of crystallization, which can be removed through heating; when rehydrated, the original properties can be restored.
Plaster of Paris
- Heating gypsum produces plaster of Paris, used in medicine for immobilizing broken bones, showcasing the transformation of materials upon heating.### Chemical Reactions Involving Calcium Sulfate
- Calcium sulfate hemihydrate (CaSO4·0.5H2O) is known as Plaster of Paris, while its dihydrate form (CaSO4·2H2O) is referred to as Gypsum.
- The formula indicates that two units of CaSO4 share one water molecule; hence, half a water molecule is represented.
- Plaster of Paris is extensively used for making toys, decor materials, and for smoothing surfaces.
Key Compounds and Reactions
- Calcium oxychloride (Ca(OCl)2) is commonly known as bleaching powder.
- Calcium hydroxide mixed with chlorine produces bleaching powder.
- Sodium carbonate (soda ash) is used for softening hard water.
- Heating sodium bicarbonate leads to decomposition, producing sodium carbonate, carbon dioxide, and water:
- NaHCO3 → Na2CO3 + CO2 ↑ + H2O
Properties of Acids, Bases, and Salts
- Acid-base indicators are dyes that signify the presence of acids or bases.
- Acids produce H+ ions, while bases generate OH- ions in solution.
- Reaction between acids and metals yields hydrogen gas and salts.
- Acid + Carbonate → Salt + CO2 + H2O.
- Both acids and bases can conduct electricity due to ion production in water.
pH Scale and Neutralization
- pH scale ranges from 0 to 14; a pH of 7 indicates neutrality, below 7 is acidic, and above 7 is basic.
- Factors affecting metabolic activities in living beings relate to the optimal pH range.
- Neutralization: Acids react with bases to form salts and water, a principle applied in various chemical applications.
Additional Notes on Water and Acids
- Water of crystallization refers to water molecules integrated into the structure of a salt.
- Distilled water, being pure, does not conduct electricity due to the absence of dissolved ions, unlike rainwater, which contains impurities.
Synthesis and Observations
- Mixing concentrated acids or bases with water is exothermic, liberating heat.
- Natural compounds can serve as indicators of acidity. For example, beetroot juice changes color in different pH environments.
- Fire extinguishers utilize reactions between acids and metal hydrogencarbonates to produce carbon dioxide, demonstrating an effective method for fire control.
Practical Applications
- Plaster of Paris should be kept dry, as it is hydrophilic and can react with moisture to revert to gypsum.
- Understanding reactions and principles of acid-base interactions is critical for applications in industries and everyday life.
Group Activities
- Students can engage in activities like preparing natural indicators and creating a soda-acid fire extinguisher, enhancing hands-on learning and understanding of concepts.
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