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Class 10 Science chapter 2 Acids, Bases and Salts notes

CHAPTER-2 ACIDS, BASES AND SALTS

  • WHAT DO WE KNOW?

→Acids are sour and change the color of blue litmus to red.

→Bases are bitter and change the colour of the red litmus to blue.

•Natural indicators of acid-base.

→Litmus, turmeric, synthetic indicators methyl orange and phenolphthalein.

•Litmus solution is a dye, which is extorted from lichen plants, when the litmus solution is neither acidic nor basic its colour is purple.

•WHAT IS ACID?

A solution that has an excess of H+ ions Sour in taste.

COMMON ACIDS-

→Acetic acid (CH3-COOH); vinegar, acetate

→Carbonic acid (H2CO3): soft drinks

→   The citric acid (C6H8O7): citrus fruits

→ Hydrochloric acid (HCL): stomach acid

→Nitric acid (HNO3): fertilizer, explosives

→Sulfuric acid (H2SO4); car batteries

•WHAT ARE THE BASE?

→A solution that has an excess of OH- ions Or

→A substance that accepts H+ ions

→Bitter in taste and soapy in touch.

COMMON BASES-

•alkaline – sodium hydroxide (NaOH), potassium hydroxide (KOH).

(water-soluble bases are alkalis) H2O+H2O→H3O+OH-

→sodium carbonate (Na2CO3) dish detergent

→sodium bicarbonate/sodium hydrogen carbonate (NaHCO3);baking soda

CHEMICAL PROPERTIES OF ACIDS AND BASES ACID-BASE INDICATORS

→Litmus solution-natural Indicator, purple in colour, acids turn blue litmus red

Bases turn red litmus blue

→red cabbage leaves-acid-red, base-green, neutral-blue

→the turmeric-acid yellow colour of turmeric remains yellow, In bases, yellow turns red.

→The Onions-smell of onion diminishes in a base and remains as it is in acid.

→the vanilla essence-the odour of vanilla essence disappears when it is added to the base.

The odour of vanilla essence persists when it is added to an acid.

So there are some substances whose odour changes in acidic or basic media. These are called olfactory indicators like onion, vanilla essence, clove.

Note-water (H2O) can be both acid and a base i

It can be considered an acid in some reactions and a base in others. Water can also reacts with itself to form acids and base.

2. ACIDS AND BASE REACTS WITH METALS.

ACID+METALS→SALT + HYDROGEN GAS

→metals displace hydrogen from the acids and form salt and hydrogen gas. (displacement reaction)

So acids react with only those metals which are placed above hydrogen so that metals can displace hydrogen from acids.

Zn+H2SO4→ZnSO4+H2

*Bases reacts with some metals to form salt and hydrogen gas

Zn+2NaOH→NaZnO2+H2

(sodium zincate)

QUESTION-

1)Why should curd and sour substance not be kept in brass and copper vessels? Solution-

ACID +Cu→Salt+H2 (curd) (harmful salt )

3). Acids with metals carbonates and metal hydrogen carbonate Solution-

Na2CO3(s)+2HCL(aq) →2NaCL(Aq)+H2O+CO2 NaHCO3+HCL→NaCL+H2O+CO2

On passing the CO2 Gas evolved through lime water. Ca(OH2)+CO2→CaCO3+H2O

All metal carbonates and hydrogen carbonates react with acids to give a corresponding salts, carbon dioxide and water.

METALS CARBONATE/METALS HYDROGEN CARBONATE + ACIDS→ SALT+CO2+WATER

*base does not react with metal carbonates.

  • Acids and bases react with each other. Base +acid→salt +water

Solution-

The reaction between an acid and a base to give salt and water is known as a neutralization reaction.

NaOH +HCL→NaCl+water

  • Reaction of metallic oxides with acids Solution-

Metal oxides +acid → salt +water Metallic oxides are basic.

Therefore acids react with metallic oxides to form salt and water. Cuo+HCL→CuCL2+H2O

  • Reaction of a Non-metallic Oxide with base Solution-

Non-metallic oxides and acidic. Bases react with non-metallic oxides to form salt and water.

Non metal-oxide+ Base→Salt +water Conclusion – Nonmetallic oxides are acidic.

# COMMON TERMS IN ALL ACIDS AND ALL BASES.

  • All acid and base conduct Electricity
    • all acids generate hydrogen gas by reacting with metals.

-An acidic solution is the useful inflow of electric current through the solution. The Electric current is carried through the solution by ions.

Since the cation present in acids is h+ this suggests that acids produce hydrogen ions, H+ in solution which is responsible for their acidic properties.

*AN ACID OR BASE IN A WATER SOLUTION?[IMP ]

When acid is dissolved in an aqueous solution then hydrogen ions in Acid are produced in the presence of water.

The separation of H+ ions from Acid solution cannot occur in the absence of Water.

HCL+H2O→ H3O+ + CL-

Hydrogen ions cannot exist alone, but they exist after combining with water molecules. Thus hydrogen ions must always be shown as H+(aq) on hydronium ions

*When a base is dissolved in water.

NaOH(s) →Na+(aq)+OH- KOH →H2O→k++OH-

The base generates hydroxide ions in water bases which are soluble in water are called alkalis.

The NOTE:

-All base does not dissolve in the water But an alkali is a base that dissolves in water.

#QUESTIONS

Que )Why does an aqueous solution of acid conduct electricity Soln) free ions helpful for flowing of electric currents.

Que 2) why does dry HCl gas not change the colour of the dry litmus paper?

Ans for acidic nature, a substance should have H+ free ion and fry HCL does not have H+ ion.

Que3)why do HCl, HNO3, etc show acidic characters in aq solution while the solution of compounds like alcohol and glucose do not have show acidic character?

Ans – Because of the H+ ion,

When HCL, HNO3 dissolve in water it separates H+ ions in a solution When alcohol and grouse are put in water it does not separate H+ ions.

#THE PROCESS OF DISSOLVING AN ACID OR BASE IN WATER IS A HIGHLY EXOTHERMIC.

So if water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns.

So the mixing of water slowly with constant stirring decrease the concentration of ions (H3O+/OH-) per unit volume such a process is called dilution.

#PH

STRENGTH OF ACID AND BASE

The strength of acids and bases depends on the number of H+ ions and OH- i ions produced, respectively.

A scale for measuring hydrogen ion concentration in a solution is called the pH scale.

The p in pH stands for ‘Potenz’ in German on the pH scale we can measure pH from0 to 14. 0-very acidic

14-very alkaline              pH-potential of Hydrogen

So pH is a number that indicates the acidic or basic nature of a solution.

A PH OF A NEUTRAL SOLUTION IS -7

A VALUE LESS THAN 7- AN ACIDIC SOLUTION VALUE MORE THAN 7-A BASIC SOLUTION

#PH IN EVERYDAY LIFE PLANTS AND ANIMALS –

Our body works within the pH range of 7.0 to 7.8. A living organism can survive only in a narrow range of pH changes.

When the pH of rainwater is less than 5.6 it is called acidic rain. When acid rain flows in rivers, it lowers the pH of river water and become difficult to survive aquatic life.

SOIL-

The optimum pH range for most plants is below 6 to 7.5

DIGESTIVE SYSTEM-

Our Stomach produces Hydrochloric acid (HCL).

It helps in the digestion of food without harming the stomach. During indigestion, the stomach produces too much acid and the causes incitation and pain.

To get rid of this pain, bases are used called. antacids. ( for neutralization) Eg: Antacids- Magnesium hydroxide (Mg(OH)2)

TOOTH DECAY-

Tooth decay starts when the pH of the month is lower than 5.5.

Bacteria present in the mouth produce acid by degradation of sugar and food particles remaining in the mouth after eating.

The best way to prevent this is to clean the mouth after eating food using toothpaste which are basic, and neutralize the excess acid and prevent tooth decay.

SELF DEFENSE BY ANIMALS AND PLANTS.

Bee-sting leaves an acid that causes pain and irritation. The use of mild bases like baking soda on the stung area gives relief.

Stinging hair of nettle leaves injects methanoic acid cause burring pain. Dock plant leaf works as a remedy

#COMMON SALT-

The common salts are contained in an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing soda, bleaching powder and many more.

1)* SODIUM HYDROXIDE (NAOH)

When electricity is passed through an aqueous solution of sodium chloride called brine, it decomposes to form sodium hydroxide. the process is called the chlor-alkali process because the products formed chlor for chlorine and alkali for sodium hydroxide.

2NaCL+2H2O→2NaOH +CL2 +H2

Chlorine gas is given off at the anode and hydrogen gas at the cathode and sodium hydroxide solution is formed near the cathode.

2.)* BLEACHING POWDER-

Bleaching powder is produced by the action of chlorine on dry slacked lime. Bleaching powder is represented as CaOCL2.

Ca(OH)2+Cl2→CaOCl2+H2O

USES Of BLEACHING POWDER

  1. for bleaching cotton and linen in the textile industry for bleaching wood pulp in paper factories and for bleaching washed clothes in the laundry.
  2. As an oxidizing agent in chemical industries.
  3. for disinfecting drinking water to make it free of germs.

3.)BAKING SODA –

The chemical name of the compound is sodium hydrogen carbonate (NaHCO3) produced from sodium chloride.

It works as a mild non-corrosive base.

The following reaction takes place when it is heated during cooking-

USE OF SODIUM HYDROGEN CARBONATE

For making baking powder, which is a mixture of baking soda and mild edible acid such as tartaric acid.

When baking powder is heated or mixed in water, the following reaction takes place-

NaHCO3+H+→CO2+H20+sodium salt of the acid

CO2 produced causes bread or cake to rise to make them soft and spongy. Baking soda is also an indigent in antacid being alkaline,

it neutralizes excess acid in the stomach and provides relief. So,Used in soda -fire extinguishers.

4.) WASHING SODA-

Chemical obtained from sodium chloride is Na2CO3.10H2O(washing soda) Crystallizing sodium carbonate gives washing soda.

It is also a basic salt.

Na2CO3+10H2O→Na2CO3.10H2O

(Washing soda)

USES OF WASHING SODA-

  • Sodium carbonate is used in glass, soap and paper industries.
  • It is used in the manufacture of sodium compound’s such as borax
  • Used as a cleaning agent for domestic purposes
  • Used for removing the permanent hardness of the water.

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