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NCERT Class 10 Science Textbook Chapter 2 With Answer PDF Free Download
Chapter 2: Acids, Bases, and Salts
You have learned in your previous classes that the sour and bitter tastes of food are due to acids and bases, respectively, present in them.
If someone in the family is suffering from a problem of acidity after overeating, which of the following would you suggest as a remedy– lemon juice, vinegar, or baking soda solution?
Which property did you think of while choosing the remedy? Surely you must have used your knowledge about the ability of acids and bases to nullify each other’s effect. Recall how we tested sour and bitter substances without tasting them.
You already know that acids are sour in taste and change the color of blue litmus to red, whereas, bases are bitter and change the color of the red litmus to blue. Litmus is a natural indicator, turmeric is another such indicator.
Have you noticed that a stain of curry on a white cloth becomes reddish-brown when soap, which is basic in nature, is scrubbed on it?
It turns yellow again when the cloth is washed with plenty of water. You can also use synthetic indicators such as methyl orange and phenolphthalein to test for acids and bases.
In this chapter, we will study the reactions of acids and bases, how acids and bases cancel out each other’s effects, and many more interesting things that we use and see in our day-to-day life.
2.2 What Do All Acids And All Bases Have In Common?
In Section 2.1 we have seen that all acids have similar chemical properties. What leads to this similarity in properties?
We saw in Activity 2.3 that all acids generate hydrogen gas on reacting with metals, so hydrogen seems to be common to all acids. Let us perform an Activity to investigate whether all compounds containing hydrogen are acidic.
|No. of Pages||20|
|PDF Size||4.3 MB|
NCERT Solutions Class 10 Science Chapter 2 Acids, Bases, and Salts
1. You are given three test tubes. The three test tubes contain distilled water, acidic solution, and the basic solution respectively. There is only red litmus paper available in order to identify what is there in each test tube. How will you find out what is in each of the test tubes?
Solution: We can identify the content in each of the test tubes using red litmus paper. This can be done by noticing the color change of the red litmus paper.
- On litmus paper, the three solutions in the test tubes are poured separately.
- The solution which turns red litmus to blue contains a basic solution.
- Divide the formed blue litmus paper into two parts.
- The solution from the test tube which turns blue litmus paper to red will be the acidic solution.
- Solution of the test tube which does not change either red or blue litmus paper contains water.
NOTE: After immediate distillation, distilled water has a pH of 7. However, just within a few hours after distillation, it absorbs carbon dioxide from the atmosphere and turns slightly acidic with a pH of 5.8.
1. Why should curd and sour substances not be kept in brass and copper vessels?
Solution: Curd and sour food substances contain acids; these acidic substances combine with metal. This reaction turns food into poison which damages people’s health.
2. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Solution: When an acid reacts with any metal, salt and hydrogen gas are formed.
Metal + Acid → Salt + Hydrogen gas
3. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Solution: As the metal compound released is Calcium Chloride the gas evolved here is CO2. Hence metal A should be Calcium Carbonate. Hence the reaction between Calcium Carbonate and HCl is
CaCO3 (s) + 2HCl (Aq) → CaCl2( Aq) + CO2 (g) + H2O (l)
intext questions set 3 Page number – 25
1. Why do HCl, HNO3, etc., show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Solution: Release of H+ ion in water will make a compound acidic or non-acidic. Acids are a substance that upon dissociating with water results in the production of hydrogen ions.
Some compounds show acidic character as they dissociate in the aqueous solution which results in the production of hydrogen ions (acids like HCl, HNO3).
Compounds similar to glucose or alcohol do contain hydrogen elements but they do not show signs of acidic nature. The fact that the hydrogen in them will not separate like the hydrogen in the acids. They will not separate to become hydrogen ions, on dissolving in the water.
2. Why does an aqueous solution of acid conduct electricity?
Solution: Charged particles are responsible for the conductance of electricity in an acid. These charged particles called ions are the reason behind the conductance of electricity in acid.
3. Why does dry HCl gas not change the color of the dry litmus paper?
Solution: HCl does not give out Hydrogen ions, therefore HCl does not show any acidic behavior, and color of the litmus paper remains the same in reaction with HCl gas.
4. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Solution: While diluting an acid, it is recommended that the acid should be added to water and not water to the acid because if water is added to a concentrated acid, it releases a huge amount of heat which may result in an explosion and can cause acid burns on the face, clothes and body parts. Hence it is safe to add acid to water but not water to acid.
5. How is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?
Solution: When acid is added to water there will be a fixed amount of hydronium present in the fixed volume of solution. If we dilute the solution hydronium ion per volume of solution decreases, this, in turn, decreases Hydronium concentration in the solution.
6. How is the concentration of hydroxide ions (OH–) affected when excess base is dissolved in a solution of sodium hydroxide?
Solution: When the base is dissolved in sodium hydroxide solution its hydroxide ions increase but it will reach saturation at some point. After saturation point hydroxide ion concentration is not affected even after adding base further.
Acids, Bases, and Salts NCERT Textbook With Solutions PDF Free Download