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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?

Hydrogen gas. Signup and view all the answers

The reaction of an acid with a base can be summarized as: Base + Acid → + .

Salt + Water Signup and view all the answers

What color does phenolphthalein turn in the presence of a base?

Pink Signup and view all the answers

All acids produce hydroxide ions in water.

False Signup and view all the answers

What happens to copper oxide when it reacts with dilute hydrochloric acid?

It dissolves, turning the solution blue-green due to the formation of copper(II) chloride. Signup and view all the answers

Which of the following is a common indicator used to test for acids and bases?

All of the above Signup and view all the answers

What do bases generate in water?

Hydroxide ions (OH–). Signup and view all the answers

What is the common name of the compound CaOCl2?

Bleaching powder Signup and view all the answers

Name the substance which on treatment with chlorine yields bleaching powder.

Calcium hydroxide Signup and view all the answers

Name the sodium compound which is used for softening hard water.

Sodium carbonate Signup and view all the answers

What will happen if a solution of sodium hydrogencarbonate is heated? Give the equation of the reaction involved.

It decomposes to form sodium carbonate, water, and carbon dioxide. The reaction is: NaHCO3 → Na2CO3 + H2O + CO2 Signup and view all the answers

Write an equation to show the reaction between Plaster of Paris and water.

CaSO4.H2O + H2O → CaSO4.2H2O Signup and view all the answers

What is water of crystallisation?

The fixed number of water molecules present in one formula unit of a salt. Signup and view all the answers

Which of the following types of medicines is used for treating indigestion?

Antacid Signup and view all the answers

A neutral solution has a pH of exactly 7.

True Signup and view all the answers

What happens when dilute hydrochloric acid reacts with magnesium ribbon?

Reacts vigorously and produces hydrogen gas. Signup and view all the answers

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?

Solution D Signup and view all the answers

What happens to the pH of fresh milk as it turns into curd?

Decreases Signup and view all the answers

Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?

HCl, HNO3, and similar acids dissociate in water to release H+ ions, while alcohol and glucose do not dissociate into ions. Signup and view all the answers

Why does an aqueous solution of an acid conduct electricity?

An aqueous solution of an acid conducts electricity due to the presence of free-moving ions. Signup and view all the answers

Why does dry HCl gas not change the color of dry litmus paper?

Dry HCl gas does not change the color of dry litmus paper because it does not release ions in its gaseous state. Signup and view all the answers

While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

Acid should be added to water to prevent exothermic reactions that could cause splattering and burns. Signup and view all the answers

How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?

The concentration of hydronium ions (H3O+) decreases when a solution of an acid is diluted. Signup and view all the answers

How is the concentration of hydroxide ions (OH−) affected when excess base is dissolved in a solution of sodium hydroxide?

The concentration of hydroxide ions (OH−) increases when excess base is dissolved in a solution of sodium hydroxide. Signup and view all the answers

Which solution has more hydrogen ion concentration: A (pH 6) or B (pH 8)?

Solution A has more hydrogen ion concentration. Signup and view all the answers

What effect does the concentration of H+(aq) ions have on the nature of the solution?

The concentration of H+(aq) ions determines whether the solution is acidic, basic, or neutral. Signup and view all the answers

Do basic solutions also have H+(aq) ions? If yes, then why are these basic?

Yes, basic solutions also have H+(aq) ions; they are basic because they have a higher concentration of OH− ions. Signup and view all the answers

Under what soil conditions would a farmer treat the soil with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?

A farmer would treat the soil if it is too acidic. Signup and view all the answers

Which of the following acids is formed from vinegar?

Acetic acid Signup and view all the answers

What is the salt formed by the combination of hydrochloric acid and sodium hydroxide?

Sodium chloride Signup and view all the answers

What chemical is commonly used as a remedy for excess stomach acid?

Magnesium hydroxide, commonly known as Milk of Magnesia. Signup and view all the answers

Match the following naturally occurring acids with their natural sources:

Vinegar = Acetic acid Orange = Citric acid Sour milk (Curd) = Lactic acid Lemon = Citric acid Ant sting = Methanoic acid Nettle sting = Methanoic acid Signup and view all the answers

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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