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NCERT Book Notes for Class 10th, Answers to Intext Questions All the questions and answers related to this lesson have been explained in detail. We will answer every question related to you.
Lesson = 2 acids, bases and salts.
Notes:-
acids and bases
• Acids are sour in taste and they turn blue litmus paper red.
• Alkalis are bitter in taste and they turn red litmus paper blue.
• Acids give hydrogen ions in aqueous solution whereas bases give hydroxide ions in aqueous solutions.
• Litmus paper is a natural indicator that identifies acids and bases.
• Synthetic indicator methyl orange gives red color in acidic medium whereas phenolphthalein gives pink color in alkaline medium.
• Litmus solution is a purple colored pigment which comes out from the lichen plant of Thallophyta group. It is neither an acid nor a base This solution is also used to identify acids and bases.
• Turmeric is also a natural indicator that identifies acids and bases. When vegetable stains on white cloth are cleaned with soap of alkaline nature, they do not get cleaned because those spots are of alkaline nature, so their effect can be reduced. To eliminate, acid is rubbed on the spots so that they are easily cleaned because acid and base neutralize the effect of each other.
• If a person is suffering from acidity then he should use banking soda for treatment as it is alkaline in nature which neutralizes the effect of acid.
• Some other natural substances like red cabbage, petunia and geranium like colored petals of flowers indicate the presence of acid and base in a solution, these are called acid-base indicator.
Natural sources of some acids:-
Citric acid is present in oranges and lemons.
• Vinegar contains acetic acid.
• Tomatoes contain oxalic acid.
• Tamarind contains tartaric acid.
• Yogurt contains lactic acid. Lactose sugar is present in milk, when it is converted into lactic acid, curd is formed.
• Ant and nettle stings contain methanoic acid.
The saliva released from the salivary glands in our mouth is alkaline in nature.
Following are the chemical properties of acids and bases:
1. odorant indicator
2. Reaction of acids and bases with metals
3.Reaction of metal carbonate and metal hydrogen carbonate with acid
4. Interaction between acids and bases
5. Reaction of Metallic Oxides with Acids
6. Reactions of non-metallic oxides with bases.
1. Aromatic Indicator:-
Substances whose odor changes in acidic or alkaline medium are called odorants.
2. Reaction of acids and bases with metals:-
Acids and bases react with metals to liberate hydrogen gas and form corresponding salts.
This reaction can be written as-
Acid or base + metal ---> salt + hydrogen gas!
acid and base reaction
Let us understand this through an experiment.
Remember that hydrogen gas burns with a bursting sound. 5ml dilute sulfuric acid is taken in a test tube, granular zinc is added to it, zinc granules react with sulfuric acid to release the gas, bubbles are formed when this gas is passed through soapy water. When a burning candle is taken near the bubbles, these bubbles burst with a bursting sound and the hydrogen gas starts burning, so it is clear that hydrogen gas was present in the bubbles. Similarly, alkalis also react with metals to liberate hydrogen gas, so it is clear that acids and bases react with metals to form corresponding salts and release hydrogen gas.
3.Reaction of metal carbonate and metal hydrogencarbonate with acid:-
Metal carbonate and metal hydrogencarbonate react with acids to form corresponding salts, carbon dioxide and water.
Reaction :-
Metal Carbonate / Metal Hydrogencarbonate --> Salt + Carbon Dioxide + Water
The products obtained are limestone, chalk and marble, various forms of calcium carbonate.
4. Interaction between acids and bases:-
Acid and base react with each other to form salt and water, this reaction is called neutralization reaction.
The neutralization reaction can be written as
Acid + Base --> Salt + Water
Acid and base react to form neutral solution by neutralizing each other's effect. Therefore, this reaction is called neutralization reaction. Do acids and bases actually neutralize each other's effect?
Interaction between acids and bases:-
Let us understand through an experiment-
Take 2ml of sodium hydroxide (alkali) solution in a test tube and add two drops of phenolphthalein solution to it. Phenolphthalein solution gives pink color in alkaline medium which indicates that it is a base. Now put a drop of dilute hydrochloric acid in this solution and see that the pink color starts disappearing i.e. the alkaline nature is less. Because hydrochloric acid reacts with sodium hydroxide to form sodium chloride and water. Now if a few more drops of sodium hydroxide are added to this solution, the pink color starts coming again, so it is clear that acid and base neutralize each other's effect.
5. Reaction of metallic oxides with acids:-
When acids react with metallic oxides, they form salts and water like the reaction of acids and bases. Since salt and water are formed by the reaction of base and acid, it can be concluded that metallic oxides are bases which react with acids to form salt and water.
6. Reactions of non-metallic oxides with bases:-
Non-metallic oxides react with bases to form salts and water, since the reaction of bases and acids forms salt and water, so it can be concluded that non-metallic oxides are acids.
Similarities between Acids and Bases:-
All acids react with metals to release hydrogen gas. Acidic solutions conduct electric current due to the presence of hydrogen positive ions in acids whereas alkaline solutions do not conduct current because they lack hydrogen cations.
Hence, it can be concluded that all the compounds in which hydrogen cations are present are acidic in nature.
How do acids and bases react in aqueous solutions?
Hydrogen cations cannot exist in a free state but can exist as H+ ions along with water molecules.
Hence it can be concluded that acids give hydrogen cation in aqueous solution.
The following reaction takes place when bases are dissolved in water:-
Bases give hydroxide ions to water. All bases do not dissolve in water Those bases which are soluble in water are called bases, they touch like soap. These should not be touched or tasted as they are highly harmful.
Since acids give hydrogen (H+) ions in aqueous solutions and bases give hydroxide (OH-) ions in aqueous solutions, the neutralization reaction can be written as -
Acid + Base --> Salt + Water
When an acid base is added to water, excessive heat is produced. Hence it is an exothermic process.
Is heat actually produced when an acid or a base is added to water, let's understand it through an experiment
Taking 10 ml of water in a beaker, while stirring it, slowly add a few drops of acid or base to it, then see that the glass beaker starts heating because heat is generated in the exothermic reaction, so it is an exothermic process.
On adding an acid or a base to water, the number of ions per unit volume decreases, this process is called dilution and in this process the acid or base is diluted.
Strength of solutions of acids and bases:-
Using indicators, we can find out whether a solution is an acid or a base but whether it is strong or weak, we cannot test it with the help of indicators.
A scale was developed to determine the concentration of hydrogen ions present in a solution called the pH scale. It is a combination of universal indicators. The pH scale displays different concentrations of hydrogen ions with different colors. Which shows whether a solution is strong or weak. pH has the symbol P which is a German word meaning power.
If the pH of a solution is less than 7 then the acidic pH of the solution is 7 and the pH is more than 7 then the solution is alkaline.
As the pH value decreases, the acidic nature increases and the alkaline nature decreases. The lower the pH value, the stronger the acid.
The alkaline nature increases as the pH value increases. And the acidic nature decreases. The higher the pH value, the stronger the alkali.
pH values of some major substances
The pH value of gastric juice is about 1.2. Hence it is a strong acid.
The pH value of lemon juice is about 2.2. Hence it is a weak acid.
Pure water has a pH of 7.4. So it's almost indifferent.
The pH value of blood is 7.4.
The pH value of Milk of Magnesia is 10. Hence it is a weak base.
The pH value of sodium hydroxide is 14. Hence it is a strong alkali.
pH value of salts:-
The pH value of salts depends on the strengths of the acids and bases participating in the reaction. If both the acid and the base participating in the reaction are strong, a neutral salt is formed. A salt formed by the reaction of a strong acid and a weak base is acidic. And the salt obtained by the action of strong base and weak acid is alkaline.
strength of acids and bases
The strength of acids and bases depends on the presence of hydrogen ions and hydroxide ions in the solution, respectively.
Acids which give more number of hydrogen ions in solution (water), are called strong acids and acids that give less number of hydrogen ions are called weak acids.
The bases which give more number of hydroxide ions in the solution are called strong bases and the bases which give less number of hydroxide ions are called weak bases.
Importance of pH in our daily life
Following are the importance of pH in our daily life-
1. Sensitivity to pH of Plants and Animals
The pH value of our body is around 7 to 7.8. We see some unusual symptoms when the value of pH decreases or increases. And the actions taking place in our body have the opposite effect.
If the pH value of rain water is less than 5.6, then such rain is called acid rain. The survival of the living beings becomes difficult due to this rain water. And aquatic creatures also get death.
2. pH of Garden Soil
Plants require a specific pH range for good yield. Neutral soil is suitable for the growth and development of plants.
3. The pH of our Digestive System
Hydrochloric acid (strong acid) comes out from our stomach. Which helps in the digestion of food without causing any harm. In the case of indigestion, the stomach (stomach) produces hydrochloric acid in excess. Due to which pain and burning starts in the abdomen. To get rid of this pain, alkalis like antacids are used.
4. Tooth decay due to pH:-
Tooth decay occurs when the pH of the mouth is less than 5.5. Tooth enamel is made of calcium phosphate, which does not dissolve in water, it is the hardest substance in the body. The bacteria present in the mouth decompose the residues and sugars left in the mouth after meals and produce acid due to which the pH value of the mouth starts falling below 5.5, in which case tooth decay starts. Tooth decay can be prevented with alkaline nature toothpaste. (Cleaning the teeth after a meal cleans the residue, so acids also do not produce bacteria. Hence, tooth decay does not occur.)
5. Self defense against chemicals produced by animals and plants
The sting of a bee releases an acid. Which causes pain. Rubbing a weak base like banking soda on the stung area provides relief.
Chemicals from common salt:-
The chemical formula of common salt is NaCl. It is a salt. Which is obtained by the reaction of hydrochloric acid and sodium hydroxide. Salt was an important symbol in India's freedom struggle.
Salt is a raw material for the manufacture of many substances used in our daily life like sodium hydroxide, baking soda, washing soda, bleaching powder etc.
Past Question Answer :-
1. Which sodium compound is used to soften hard water?
Sodium carbonate is used to soften hard water.
2. Name the substance which reacts with chlorine to form bleaching powder?
Calcium oxide reacts with chlorine to form bleaching powder.
3. Which gas is released when an acid reacts with a metal?
When an acid reacts with a metal, hydrogen gas is released.
4. Phenolphthalein gives pink color in solution of which nature?
Phenolphthalein gives pink color in solutions of basic nature.
5. Who is called Brine?
A concentrated aqueous solution of sodium chloride is called brine.
6. A liquid substance reacts with the ground shell of an egg to produce a gas which turns lime water milky, what will be the name of this liquid substance?
HCl acid. The name of the gas released in the reaction will be carbon dioxide.
7. What is the reason that the pH value of saliva is higher before meals and lower after meals?
The pH value of saliva is 7.4 before a meal and 5.8 after a meal. Because the bacteria present in the mouth after a meal decompose the residues and sugars to produce acid, which increases the acidic nature of saliva and decreases the pH value.
8. Name the indicator which gives red color in acidic solution.
An indicator called methyl orange gives red color in acidic solution.
9. Name the acid found in the hair or sting of nettle.
Methanoic acid or formic acid is found in the sting of the nettle.
10. Milky color disappears when more carbon dioxide is passed through lime water, why?
When a large amount of CO2 gas is passed through lime water, calcium hydrogen carbonate is formed, which removes the milkiness of lime water and purifies the solution.
11. What is the change in the color of litmus paper by alkali and acid?
Acids turn blue litmus paper red. And alkalis turn red litmus paper blue.
12. Why does the pH decrease when curd is formed?
The pH of fresh milk is 6. But when curd is formed, the pH becomes less than 6 due to the formation of lactic acid.
13. What is Universal Indicator?
Universal indicator is a combination of many different indicators. Universal indicator sheet gives different colors for different pH values of the entire pH scale. Its color is dark red for 0, green for 7 and its color for 14 is purple.
14. What is the pH of a salt made up of a strong acid and a weak base?
The pH value of a salt made of a strong acid and a weak base is less than 7 because whichever of the acid or base is stronger, the nature of the salt will also be acidic or alkaline accordingly. A salt formed from a strong acid and a strong base shows a neutral nature.
15. Why should sour food items not be kept in copper and brass utensils?
Sour substances are not kept in brass, copper or other metal utensils because the acids present in sour substances react with metal utensils to form toxic metal compounds. Which can cause harm to our health by causing food poisoning.
16. Compounds like HCl, HNO3 etc. show acidic properties in aqueous solution whereas glucose and alcohol do not. Why?
Compounds like HCl, HNO3 etc. give hydrogen cation (H+) ions in aqueous solution, so they are kept in the category of acids, whereas alcohol and glucose are not kept in the category of acids even though they contain hydrogen, because these compounds in aqueous solution are kept in the category of acids. Hydrogen does not give cation.
17. Why does dry HCl gas not change the color of dry litmus paper?
Dry hydrochloric gas does not change the color of dry litmus paper because HCl gas does not show acidic behavior in the absence of water. In dry state HCl gas does not give H+(aq) ion and we know that H+(aq) ion is necessary to change the color of litmus paper. Therefore, dry HCl gas does not change the color of litmus paper, but if litmus paper is taken wet or dry HCl gas is dissolved in water, it exhibits acidic properties by changing the color of litmus paper from blue to red.
18. What are acids called? Write the names of any two strong acids. Write the properties of acids?
Acids are those which give H+(aq) ions in aqueous solution and turn blue litmus red.
Examples of strong acids - HCl, H2SO4
Properties of acids
1. Acids react with metals to give hydrogen gas.
Acid + Metal → Salt + Hydrogen Gas
2. Acids react with a metal carbonate and a metal hydrogen carbonate to give carbon dioxide gas.
Acid + Metal Carbonate or Metal Hydrogen Carbonate → Salt + Carbon Dioxide + Water
19. Write the name and use of CaOCl2 compound?
CaOCl2 compound is a bleaching powder. Which is used for bleaching cotton and linen in the textile industry, wood pulp in the paper factory and bleaching of clothes in the laundry, as an auxiliaries in industries, as a disinfectant to make drinking water free from bacteria, etc. is done.
Other important questions:-
1. Name two compounds which contain hydrogen but are not acids and do not conduct electricity in their solution. Alcohols (C2H5OH) and Glucose (C6H12O6)
2. The method of measuring the concentration of hydrogen ion was given by which scientist?
Sorenson.
3. What is the pH of tomato juice?
Tomato juice is acidic. Its pH value is 4.0-4.4.
4. Give the value of pH of human urine.
5.5-7.5
5. When Zn is treated with NaOH solution, H2 gas is obtained. Its equation will be
Zn(s) + 2NaOH(aq) = Na2ZnO2(aq) + H2
6. What is the general nature of oxides of metals? Give two examples.
Oxides of metals are generally basic in nature, e.g. CaO, MgO.
7. Give two examples of strong acids.
HCl (hydrochloric acid), H2SO4 (sulfuric acid)
8. Give two examples of strong bases.
NaOH (Sodium Hydroxide), KOH (Potassium Hydroxide)
9. Give two examples each of weak acids and weak bases.
Weak acid- CH3COOH, HCN
Weak base - NH4OH, Mg(OH)2
10. What are universal/universal indicators? write |
These are a combination of several indicators. They show different concentrations of H+ ions in a solution in different colors.
11. What is the pH of gastric juice?
The pH of gastric juice is about 1.2.
12. Which acid is found in tomato?
Oxalic acid is found in tomato.
13. Name four salts of sodium group.
Sodium sulfate, sodium chloride, sodium nitrate, sodium carbonate.
14. Aqueous solution of sodium acetate is basic. Why?
Sodium acetate (CH3COONa) is a salt made up of a weak acid (CH3COOH) and a strong base (NaOH), so its aqueous solution will be basic.
15. Which gas is obtained at cathode and anode when electricity is passed through an aqueous solution of sodium chloride?
On passing electricity through an aqueous solution of sodium chloride, H2 gas is formed at the cathode and Cl2 gas at the anode.
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1 टिप्पणियाँ
Very nice
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