Notes of chapter -2 science chapter-2 Acids,Bases and salts

Acids,Bases and salts Notes class 10th Science

• These are the substances which have sour taste.

•They turn blue litmus solution to Red.

•They give H+ ions in aqueous solution.

•The term 'acid' has been derived from the Latin word , acids, which means sour.

Strong Acid:HCl, H²SO⁴, HNO³

Weak Acid:CH³COOH, oxalic acid, lactic acid.

Concentrated Acid:Having more amount of acid+less amount of water.

Dilute Acid:Having more amount of water+less amount of acid.

Bases:

•They are the substances which are bitter in taste and soapy in touch.

•They turn red litmus solution to blue.

•They give H- ions in aqueous solution.

Strong Bases:NaOH, KOH, Ca(OH)²

Weak Bases:Na⁴OH

Alkalis:These are bases which are soluble in water [NaOH, KOH, Ca(OH)²]

Salts:

These are Compound formed from reaction of acid and base.

Example:NaCl, KCl.

Indicator:These are the substance which change colour/smell in different types of substances.

               Type of Indicators

Natural Indicator:Formed in nature in plants, litmus red cabbage leaves extract, flowers of hydrangea plant, turmeric.

 Synthetic Indicators:They are chemical substances, Methyl orange, phenolphthalein.

Olfactory Indicators:These substances have different odour in acid and bases.

               Olfactory Indicator

Chemical Properties of Acids and Bases reaction of metals with acid

Acid+Metal→salt+hydrogen gas

Eg. 2HCL+Zn→ZnCl²+H²

 Reaction of metals with Bases

Base+Metal→salt+Hydrogen gas

Eg. 2NaOH+Zn→Na²ZnO²+H²↑

                               (sodium zincate)

•Hydrogen gas released can be tested by bringing burning candle near gas bubbles, it burst with pop sound.

Reaction of Metal carbonates/Metal Hydrogen carbonates with Acids:All metal carbonates and hydrogen carbonates react with acid to give a corresponding salt, carbon dioxide and water.

Acid+Metal carbonate/Metal carbonate→salt+Co²+H²0 Base+Metal carbonate/metal hydrogen carbonate

Eg 2HCl+Na²Co³→2Nacl+Co²+H²0→No reaction

HCl+NaHCo³→Nacl+Co²+H²0

• Co² can be tested by passing it through lime water.

Co(OH)²+Co²→CaCo³+H²0(lime water turn milky)

• whenn excess Co² is passed.

CaCo³+Co²+H²0→Ca(HC0)³(milkiness disappears).

Reaction of Acid and bases with Each other

Acid + Base→salt+H²0

Neutralisation Reaction:Reaction of acid with base is called as neutralisation reaction.eg HCl+NaOH→NaCl+H²0.

If

Strong acid+weak base→Acidic salt+H²0

Weak Acid+strong base→Basic salt+H²0

Strong Acid+strong base→Neutral salt+H²0

Weak Acid+weak base→Neutral salt+H²0

Reaction of Metallic oxides with Acids

Metallic oxide are basic in nature.

Eg. Cao, Mgo are basic oxides

Metallic oxide+Acid→salt+H²0

Cao+2HCl→CaCl²+H²0

Reaction of non-metallic oxides with bases 

Non-metallic oxides are acidic in nature.

Non-matallic oxide+ base→salt+H²0

Co²+Ca(OH)²→CaCo³+H²0

What Do All Acids are Bases have in common

•All acids have H+ ions in common.

•Acids produce H+ ions in solution which are responsible for their acidic properties.

•All bases have OH- [hydroxyl ions] in common.

Note: Acids→H+ ions

           Bases→OH- ions

Acid or base in water solution

•Acids produce H+ ions in presence of water.

•H+ ions cannot exist alone, they exist as H³0+[hydronium ions]

              H+ + H²0→H³0+

        HCl + H²0→H³0+ +Cl-

Bases when dissolved in water gives OH- ions.

NaOH      H²0   Na+ +OH-

              ––––––›

Mg(0H)²  H²O  Mg+ +20H-

              ––––––›

• Bases soluble in water are called alkali.

•while diluting acids , it is recommended that the acid should be added to water to acid because the process of dissolving an acid or a base in water is highly exothermic.

•If water is added to acid, the heat generated may cause the mixture to splash out and cause burns and the glass container may also break due to excessive local heating.

•Mixing an acid or a base with H²0 result in decrease of concentration of ions [H³0+/OH-] per unit volume. Such a process is called as dilution.

Strength of acid and Base

Strength of acid or base can be estimated using universal indicator.

Universal Indicator: Universal indicator is a mixture of several indicators.It shows different colours at different Concentrations of H+ ions in the solution.

PH scale:A scale for measuring H+ ions concentration in a solution.P is stands for 'potency a German word which means power.

PH less than 7→ acidic solution

PH more than7→Basic solution

Ph=7 → neutral solution

                  Weak Acid and Base

On diluting an acid:Ph increase↑

On diluting a Base:Ph decreases↓

   Acid nature increase

<———————————     

  Basic nature increases

——————————— >  

0------------------------|--------------------------- 14

                        Natural

increase in H+ ion

<————————

Decrease in H+ ion

  ————————>

Importance of Ph in everyday life

1.Plants and animals are oh sensitive

• Our body works within the ph range of 7-7.8.

• when ph of rain water is less than 5.6,it is called acid rain.

2.Ph of the soil 

• Plants require a specific ph range for their healthy growth.

3.Ph in our digestive system

•Our stomach produces HCl acid which help in digestion.

•During indigestion, stomach produces more acid and cause pain and irritation.

•To get rid of this , pain, people uses antacid (mid base) like milk of magnesia [Mg(OH)²] to neutralise excess acid.

4.Ph change as cause of tooth decay

•Tooth decay starts when ph of mouth is lower than 5.5.

•Tooth enamel made up of calcium phosphate(hardest substance in body )

Does not dissolve in water but corrodes when ph is lower than 5.5 due to acids produced by degradation of food particles by bacteria.

•Using toothpase (generally basic) tooth decay can be prevented.

5.Self defence by animals and pop plants through chemical warfare.

(a) Bee strong leaves an acid which cause pain and irritation.Use of a mild base like baking soda on strung area gives relief.

(b)Stringing hair of nettle leaves inject mechanic acid causing burning sensation or pain .Rubbing with leaf of dock plant give Relief.

Ph of salts:

(I) Strong Acid+strong    Base→Neutral salt:ph=7

(II) Salt of strong acid +weak base→Acidic salt: Ph<7

(III) Salt of strong Base+weak acid→Basic salt:Ph>7

 Chemical from common salt (NaCl)

1.Sodium Hydroxide(NaCl)

2.Bleaching Powder (CaoCl²)

3.Baking soda (NaHCo³)

4.Washing soda (Na²Co³.10H²O)

5.Plaster Of Paris(CaSo⁴.1/2H²O)

(i)Sodium hydroxide(NaOH):when electricity is passed through an aqueous solution of NaCl (brine) , it decompose to form NaOH (chlor-alkali process).

     2NaCl+2H²O→2NaOH+Cl²+H²

At anode:Cl² gas

At Cathode:H² gas

Near Cathode:NaOH sodium is formed.

Uses:

   

H²: Fuels, Margarine

Cl²:water treatment, PVC,CFC's

HCl:Cleaning steels, medicines.

NaOH:Degreasing metals, soaps and paper making Cl²+NaOH→Bleach:Household beaches, bleaching fabrics

(ii)Bleaching Powder:(CaoCl²):It is produced by the action of chlorine on dry slaked line.

Cl²+Ca(OH)²→CaoCl²+H²O

Uses:

(a)Bleaching cotton and line in textile industry.

(b)Bleaching wood pulp in paper factories.

(c)Oxidizing agent in chemical industries.

(d)Disinfecting drinking water.

 

(iii)Baking soda(sodium hydrogen carbonate)(NaHCO³):

It is obtained by the reaction of carbon dioxide with saturated solution of ammonical brine.

•It is mild non-corrosive base.

•when it is heated during cooking.

       2NaHCo³→Na²Co³+H²0+Co²

Uses:

(a)For making baking powder (mixture of baking soda and tartaric acid).when , Co² is produced which causes bread and cake to rise making them soft and spongy.

(b)An ingredient in antacid.

(c)used in soda acids, fire extinguishers.

(IV)Washing soda(Na²Co³.10H²0):Recrystallization of sodium carbonate gives washing soda.It is a basic salt.

      Na²Co³+10H²0→Na²Co³.10H²0

Uses:

(a)In glass, soap and paper industry.

(b)Manufacture of borax.

(C)Cleaning agent for domestic purpose.

(d)For removing permanent hardness of water.

(V)Plaster of Paris (calcium sulphate hemihydrates) (CaSo⁴.1/2H²0):On heating gypsum

(CaSo⁴.2H²0) at 373k, it loses water molecules and become plaster of Paris (pop) it is a white powder and on mixing with water it changes to gypsum.

CaSo⁴.1/2H²0+0ne and half H²0→CaSo⁴.2H²0

Uses:

(a)Doctors use pop for supporting fractured bones.

(b)for making toyes, material for decoration.

(c)For making surfaces smooth.

Water of crystallization : It is a fixed number of water molecules present in one formula unit of a salt.

Eg Cuso⁴.5H²0 has 5water molecules.

Na²Co³.10H²0 has 10 water molecules.

Caso⁴.2H²0 has 2 water molecules.

NCERT Solution of Class 10th Science 

Textbook Questions and Solutions

1. What are acids and bases? Provide examples.

• Solution:
• Acids: Substances that release hydrogen ions (H⁺) in water. They have a sour taste.
  • Examples: Hydrochloric acid (HCl), Sulphuric acid (H₂SO₄).
• Bases: Substances that release hydroxide ions (OH⁻) in water. They have a bitter taste and feel slippery.
• Examples: Sodium hydroxide (NaOH), Potassium hydroxide (KOH).

2. Why do HCl, HNO₃, etc., show acidic characters in aqueous solutions while alcohol and glucose do not?

• Solution:
• HCl and HNO₃ ionise in water to produce hydrogen ions (H⁺), which is responsible for the acidic nature.
• Alcohol and glucose do not ionise in water to release H⁺ ions; therefore, they do not exhibit acidic properties in aqueous solutions.

3. Why does an aqueous solution of an acid conduct electricity?

• Solution: Acids in aqueous solutions ionise to produce free ions, which can move freely and conduct electricity. For example, hydrochloric acid (HCl) dissociates as HCl → H⁺ + Cl⁻.

4. Why should curd and sour substances not be kept in brass and copper vessels?

• Solution: Curd and sour substances contain acids that can react with brass and copper, releasing toxic compounds, which makes the food harmful. This is due to a chemical reaction between the acids and the metals.

5. What is the reaction between acids and metals? Give an example.

• Solution: Acids react with metals to produce salt and hydrogen gas.
• Example: $\text{2HCl} + \text{Zn} \rightarrow \text{ZnCl}_2 + \text{H}_2$ (Zinc chloride and hydrogen gas).

6. What do you observe when an acid or a base is added to water? Explain.

• Solution: When an acid or base is added to water, it dissociates into ions. This ionisation makes the solution conduct electricity. For instance, when HCl is added to water, it releases H⁺ ions. This process is exothermic and releases heat.

7. Why do dry HCl gas and HCl solution in water have different properties?

• Solution: Dry HCl gas does not release H⁺ ions, so it doesn’t show acidic properties. In an aqueous solution, HCl dissociates to release H⁺ ions, displaying acidic properties.

8. What happens when an acid reacts with a base?

• Solution: When an acid reacts with a base, it forms salt and water. This is known as a neutralisation reaction.
• Example: $\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}$.

9. What are salts?

• Solution: Salts are compounds formed when acids react with bases. They consist of a positive ion (from a base) and a negative ion (from an acid). Examples include sodium chloride (NaCl) and potassium nitrate (KNO₃).

10. What is pH and its importance?

• Solution: pH is a scale to measure the acidity or alkalinity of a solution. It ranges from 0 to 14:
• pH < 7: Acidic.
• pH = 7: Neutral.
• pH > 7: Basic.
• The pH of substances in our body, like blood and digestive juices, affects biological processes, making pH regulation crucial.

11. Explain the importance of pH in everyday life.

• Solution:
• Human Body: pH of blood is around 7.4; any major change can lead to illness.
• Agriculture: Soil pH affects crop growth; certain plants grow better in specific pH levels.
• Medicines: pH affects the effectiveness of medications.
• Food: Acidity in food influences preservation and taste.

12. What is a neutralisation reaction? Give an example.

• Solution: A neutralisation reaction occurs when an acid reacts with a base to form salt and water.
• Example: $\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + \text{H}_2\text{O}$.

13. How do metal carbonates and metal hydrogen carbonates react with acids?

• Solution: Metal carbonates and metal hydrogen carbonates react with acids to produce salt, water, and carbon dioxide.
  • Example: $\text{Na}_2\text{CO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + \text{H}_2\text{O} + \text{CO}_2$​

14. What happens when an acid reacts with a metal oxide?

• Solution: Acids react with metal oxides to produce salt and water, as metal oxides are basic in nature.
• Example: $\text{CuO} + \text{H}_2\text{SO}_4 \rightarrow \text{CuSO}_4 + \text{H}_2\text{O}$

15. What happens when a base reacts with a non-metal oxide?

• Solution: Bases react with non-metal oxides to produce salt and water. Non-metal oxides are acidic in nature.
• Example: $\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}$

16. Why is plaster of Paris written as CaSO₄·½H₂O? How is it different from gypsum (CaSO₄·2H₂O)?

• Solution: Plaster of Paris (CaSO₄·½H₂O) contains half a molecule of water of crystallisation. It is obtained by heating gypsum (CaSO₄·2H₂O) at 373 K, losing water and forming plaster of Paris.