Kerala SSLC Class 9 Solutions for Physical Sciences – Acids and Alkalis (English Medium) Part-2
Page No. 152:
Question 1:
Why is it necessary to reduce the acidity of the soil?
Solution :
Acidic property of soil is not suitable for cultivation of crops. To reduce this acidic property, quick lime is added to the field so as to neutralize the excess acid present in the soil for the proper growth and productivity of plants. Quick lime is used as an alkali.
Question 2:
How do we test acidity? Note down the methods you know.
Solution :
We test acidity
- By using indicators
- By checking the pH of the soil
Page No. 153:
Question 1:
Furnished below are certain statements. Examine them, find out those related to acid and ‘✓’ them in the box.
□ Reacts with metals to form hydrogen
□ Soapy to touch
□ Changes red litmus blue
□ Colourless when phenolphthalein is added
□ Changes blue litmus red
□ Carbon dioxide gas is evolved by reacting with the carbonates present in egg shell, marble, oyster shell etc.
□ Gives pink colour with phenolphthalein
□ Sour to taste
Solution :
✓ Reacts with metals to form hydrogen
□ Soapy to touch
□ Changes red litmus blue
□ Colourless when phenolphthalein is added
✓ Changes blue litmus red
✓ Carbon dioxide gas is evolved by reacting with the carbonates present in egg shell, marble, oyster shell etc.
✓ Gives pink colour with phenolphthalein
✓ Sour to taste
Question 2:
Plan some experiments to confirm that the statements you have selected are correct. (Please bear in mind that many acids and alkalis are corrosive and can cause burns on the body. So do not try to test them by either touching, smelling or tasting).
Solution :
Activity 1:
Aim: Acids react with metals to form hydrogen gas.
Materials: Zinc granules, dilute sulphuric acid, cork, delivery tube, thistle funnel, gas jar, soap solution.
Procedure:
- Take about 5 mL of dilute sulphuric acid in a test tube and add a few pieces of zinc granules to it.
- We will observe the formation of gas bubbles on the surface of zinc granules.
- Pass the gas being evolved through the soap solution.
- Gas filled bubbles are formed in the soap solution which rise into the air.
- Take a burning candle near a gas filled soap bubble.
- The gas present in soap bubble burns with a pop sound making a little explosion.
- Hydrogen gas has a unique property if burning with a pop sound.
- Repeat this Activity with some more acids like HCl, HNO3 and CH3COOH. The observation will be the same for all this acids.
Activity 2:
Aim: Acids react with metal carbonates to form carbon dioxide gas.
Materials: Sodium carbonate, dilute hydrochloric acid, test tube, delivery tube, cork.
Procedure:
- Take a boiling tube and put about sodium carbonate in it.
- Add about dilute hydrochloric acid in the boiling tube.
- We will observe that brisk effervescence of a gas is produced. Pass the gas through lime water.
- The lime water turns milky showing that it is carbon dioxide gas.
Question 3:
Examine the chemical formulae of the acids. What is the common factor seen in them?
Solution :
Hydrogen is the common factor present in all the acids. For example, H2SO4, HCl, HNO3, CH3COOH etc.
Question 4:
Examine the reaction of zinc with acids. Complete the chemical equations.
Zn + 2HCl → ZnCl2 + ……………..
Zn + H2SO4 → …………….. + ……………..
Solution :
Zn + 2HCl → ZnCl2 + H2↑
Zn + H2SO4 → ZnSO4 + H2↑
Question 5:
Butter milk, tamarind etc. are not kept in aluminum vessels. Why?
Solution :
Butter milk and tamarind are not kept in aluminum vessels because they contain acids which react with the aluminium metal to form poisonous metal compounds. These can cause food poisoning and health issues.
Question 6:
What is the substance used on farms to reduce the acidity of soil?
…………………………………………………………….
Solution :
Quick lime is used on farms to reduce the acidity of soil.
Question 7:
Is it possible to find out the characteristics of this substance using indicators? Which indicators can be used for this?
…………………………………………………………………….
Solution :
Yes. It is possible to find out the characteristics of this substance using indicators. Indicator like red litmus, blue litmus, methyl orange and phenolphthalein are used for this.
Page No. 154:
Question 1:
Examine the table given below containing substances that are alkaline in nature. Analyse the chemical formulae and fill up the common factor of alkalis, in the table.
Name | Chemical Name | Chemical formula | Common factor |
Lime | Calcium hydroxide | Ca(OH)2 | |
Caustic soda | Sodium hydroxide | NaOH | |
Caustic potash | Potassium hydroxide | KOH | |
Milk of Magnesia | Magnesium hydroxide | Mg(OH)2 |
Solution :
Name | Chemical Name | Chemical formula | Common factor |
Lime | Calcium hydroxide | Ca(OH)2 |
OH (Hydroxide) |
Caustic soda | Sodium hydroxide | NaOH | |
Caustic potash | Potassium hydroxide | KOH | |
Milk of Magnesia | Magnesium hydroxide | Mg(OH)2 |
Question 2:
In acid solutions does hydrogen exist as atoms or as ions?
Solution :
In acidic solutions, hydrogen exists as ions.
Question 3:
What about the OH group in alkalis?
Solution :
In alkalis, OH group exists as hydroxide ions.
Question 4:
The common factor acid is …………………
Solution :
The common factor in acid is H+.
Question 5:
The common factor in alkali is……………….
Solution :
The common factor in alkali is OH–.
Page No. 155:
Question 1:
What will happen when an acidic solution is mixed with an alkaline solution?
Solution :
Salt and water are formed when an acidic solution is mixed with an alkaline solution.
Question 2:
Gradually pour acid solution into sodium hydroxide solution to which a few drops of phenolphthalein are added, stirring it continuously till a visible change occurs. Observe it carefully.
What happened? Did the nature of the solution change? Test with litmus.
……………………………………………………………………………………………….
Solution :
he following changes takes place:
- Pink colour of the solution disappears.
- The solution becomes colourless.
- There is no change in the litmus.
From this we can conclude that solution is neutralized.
Question 3:
Test again after adding one or two drops of sodium hydroxide to the above solution.
What do you observe?
Solution :
Pink colour appears again.
Question 4:
Test after adding two drops of acid to the above solution. Note down your findings.
…………………………………………………………………………………………..
Solution :
Pink colour disappears and the solution becomes colourless.
Question 5:
In the activity which you performed, what happened when acid and alkali reacted with each other?
Solution :
Acid and alkali react with each other to form a neutral solution, i.e. a colourless solution.
Question 6:
Neutralization is the process in which acid and alkali react with each other to give a neutral solution.
Is it the same thing that could have happened when lime was added to the soil with acidity?
Solution :
Yes. It the same thing that could have happened when lime was added to the soil with acidity.
Question 7:
What would happen if lime is sprinkled in excess?
Solution :
If lime is sprinkled in excess to the soil, it will become alkaline in nature and will affect the crops. The soil will become too basic with a high pH. If the soil is too alkaline, then its alkalinity can be reduced by adding decaying organic matter (manure or compost) which contains acidic materials.
Question 8:
Do you know that sometimes the acidity of our stomach increases? How do you feel then? Is there any remedy for this?
Solution :
Yes, sometimes the acidity of our stomach increases.
If the quantity of acid increases, it produces a burning sensation in the stomach. Antacids are medicines used for reducing the acidity in the stomach.
Page No. 156:
Question 1:
Which acid was required in larger volume for neutralizing the same amount of alkali?
Solution :
Dilute acid is required in large volume for neutralizing the same amount of alkali.
Question 2:
If the same volumes of dilute and concentrated acids are taken, which one requires smaller volume of alkali for neutralisation?
Solution :
Concentrated acid will require smaller volume of alkali for neutralization.
Question 3:
Which is the stronger acid-vinegar or hydrochloric acid?
Solution :
Hydrochloric acid is the stronger than acid-vinegar.
Page No. 157:
Question 1:
Fill up the following.
- The pH value of acid is ………………. than 7 (less/ more)
- The pH value of alkali is …………….. than 7 (less/more)
- pH value …………. as the strength of the acid increases (increases/decreases)
- The acidity of a solution as its pH value increases (increases / decreases)
Solution :
- The pH value of acid is less than 7.
- The pH value of alkali is more than 7.
- pH value decreases as the strength of the acid increases.
- The acidity of a solution decreases as its pH value increases.
Question 2:
Find out the pH value of the following and classify them as acidic, basic or neutral.
Lemon water, milk, sugar solution, black coffee, soap solution, brine (table salt solution), baking soda solution.
Solution :
Substance | Acid/Basic/ Neutral | pH Value |
Lemon water | Acid | 2.5 |
milk | Acid | 6.5 |
sugar solution | Neutral | 7.0 |
black coffee | Acid | 5.0 |
soap solution | Basic (alkaline) | 10 |
brine (table salt solution) | Neutral | 7.0 |
baking soda solution | Basic (alkaline) | 8.5 |
Question 3:
What happened when acid was added to the alkali containing phenolphthalein?
Solution :
When acid was added to the alkali containing phenolphthalein, it was observed that the pink colour disappeared and the solution became colourless.
Question 4:
Why did acid and alkali neutralise each other?
Solution :
The common factor H+ ions in acid and OH– ions in alkali combine to form water molecule. After that the solution has no taste of acid or alkali.
Question 5:
Is it possible to neutralise any acid by using any alkali?
Solution :
Yes. It possible to neutralise any acid by using any alkali.
Question 6:
Is the presence of common factors the reason for all acids being able to neutralise all alkalis?
Solution :
Yes, the presence of common factor is the reason for all acids being able to neutralise all alkalis. The ability to neutralise mutually depends upon their pH.
Question 7:
Try to neutralise sodium hydroxide using different acids.
Try KOH instead of NaOH. Record your findings
Solution :
The reaction is given as
HNO3 + KOH → KNO3 + H2O
Potassium hydroxide and nitric acid react and neutralise to form potassium nitrate.
Question 8:
Write the chemical equations for neutralization reactions.
- NaOH+ HCl → NaCl + H2O
Solution :
Following are the chemical equations for neutralization reactions.
NaOH + HCI → NaCI + H2O
KOH + HNO3→ KNO3 +H2O
2NaOH + H2SO4→ Na2SO4 +2H2O Ca(OH)2 + 2HCI → CaCI2 + 2H2O
2KOH + H2SO4 → K2SO4 + 2H2O
Question 9:
Table shows the components of a few acids and alkalis. Fill up the table.
Alkali | Common Factor | Acid | Common Factor | Compound formed by combination of common factors | Compound formed by combination of remaining parts | |||
Chemical Formula | Ions | Chemical Formula | Ions | |||||
HCl | H+ | Cl– | NaOH | OH– |
…….. |
|||
H2SO4 | H+ | Mg(OH)2 | OH– | MgSO4 | ||||
HNO3 | H+ | Ca(OH)2 | OH– | Ca(NO3)2 | ||||
H2CO3 | H+ | KOH | OH– | K2CO3 |
Solution :
Alkali | Common Factor | Acid | Common Factor | Compound formed by combination of common factors | Compound formed by combination of remaining parts | |||
Chemical Formula | Ions | Chemical Formula | Ions | |||||
HCl | H+ | Cl– |
H+ |
NaOH | OH– |
OH– |
H2O | NaCl |
H2SO4 | H+ | Mg(OH)2 | OH– | H2O | MgSO4 | |||
HNO3 | H+ | Ca(OH)2 | OH– | H2O | Ca(NO3)2 | |||
H2CO3 | H+ | KOH | OH– | H2O | K2CO3 |
Question 10:
Name the salts that we use in our day-to-day life. Fill up the following table.
Salt | Uses |
• Sodium chloride • Potassium chloride • …………………… • …………………… • …………………… • …………………… • …………………… |
………………………………………………. Substitute for common salt for blood pressure patients, as fertilizer Nitrogen fertilizers |
Solution :
Salt | Uses |
• Sodium chloride • Potassium chloride
• Ammonium sulphate
• Sodium carbonate
• Sodium hydroxide |
To give taste to food materials and acts as a preservative Substitute for common salt for blood pressure patients, as fertilizer
Nitrogen fertilizers
To remove the permanent hardness of water for the manufacture of soap, glass.
For the manufacture of detergents, soaps. |
Page No. 158:
Question 1:
Take a look at the cations and anions of the salts given in table. Examine the numbers of each one.
Salt | Cation | Numbers | Anion | Numbers |
KCl | K+ | 1 | Cl– | 1 |
CaCO3 | Ca2+ | 1 | 1 | |
Na2SO4 | Na+ | 2 | 1 |
- Is it possible to recognize the acid and alkali from which a salt is derived, by studying its chemical formula?
- Which is the acid that contains Cl–?
- Which is the alkali that contains K+?
- Identify the acids and alkalis from which the salts given in the above table are formed.
Solution :
- Yes. It is possible to recognize the acid and alkali from which a salt is derived, by studying its chemical formula.
- HCl is the acid containing Cl– ion.
- KOH is the alkali containing K+ ion.
Salt | Acids | Alkalis |
KCl | HCl | KOH |
CaCO3 | H2CO3 | Ca(OH)2 |
Na2SO4 | H2SO4 | NaOH |
Question 2:
Find out the chemical formulae of more salts and write down their acids and alkalis in the science diary.
Solution :
Name of Salt | Chemical Formula | Alkali | Acid |
Calcium sulphate Potassium sulphate Magnesium sulphate Sodium chloride Ammonium chloride Sodium nitrate Copper sulphate Sodium carbonate |
CaSO4 K2SO4MgSO4 NaCl NH4Cl NaNO3CuSO4Na2CO3 | Ca(OH)2KOH Mg(OH)2NaOH NH4OH NaOH
Cu(OH)2NaOH |
H2SO4H2SO4H2SO4 HCl HCl HNO3H2SO4 H2CO3 |
Question 3:
In the chemical formula, where is the digit indicating the charge of the ions placed?
Solution :
The charge of the ions is written at the top right above the chemical formula.
Question 4:
While writing the chemical formula which is to be written first cation or anion?
Solution :
While writing the chemical formula, cation is to be written first.
Question 5:
Examine the chemical formula CaCl2.
Solution :
Formula of Calcium chloride
Therefore, the molecular formula of Calcium chloride is CaCl2.
Question 6:
Examine the chemical formula CaCO3.
Solution :
Formula of Calcium carbonate
Therefore, the molecular formula of Calcium chloride is CaCO3.
Page No. 159:
Question 1:
Are any of the compounds formed above used as fertilizers?
Solution :
Yes. Compounds such as ammonium sulphate, calcium phosphate, ammonium phosphate, potassium chloride, potassium sulphate are used as fertilizers.
Question 2:
In what circumstances are fertilizers used for plants?
Solution :
- Plants require a number of elements for growth.
- They get these elements from soil.
- The soil should be fertile enough if these elements are to be available.
- Crops take up nutrient elements from the soil. The tremendous growth in crops creates lack of certain nutrients in the soil.
- To avoid this we must add fertilizer to the field to replenish soil with nutrients.
Question 3:
Write down the names of chemical fertilizers and organic fertilizers you know.
Solution :
Chemical fertilizers: Urea, NPK mixtures, rock phosphate, ammonia, muriate of potash
Organic fertilizers: Cow dung, green manure, fish manure, bone powder, compost, vermicompost
Question 4:
Following are some of the salts used as chemical fertilizers.
- Ammonium sulphate – (NH4)2SO4
- Potassium chloride , KCl
- Sodium nitrate – NaNO3
Solution :
- Ammonium sulphate – (NH4)2SO4
- Potassium chloride , KCl
- Sodium nitrate – NaNO3
- Calcium phosphate Ca3(PO)2
- Potassium sulphate K2SO4
Page No. 160:
Question 1:
In what manner is the application of chemical fertilizers linked to irrigation?
Solution :
- Proper irrigation is necessary for the absorption of fertilizers.
- Excessive irrigation will extend the growth of plants.
- During the application of fertilizers there must be sufficient water in the soil.
- The insufficiency of water will affect the growth of plants.
Question 2:
How does excessive application of fertilizers affect soil?
- Microbes
- pH value
Solution :
- Excessive use of fertilizers adversely affects the nature of soil.
- The pH value of the soil is an important factor for the growth of plants.
- The use of salts such as urea, sulphate, ammonia increases the acidity of the soil.
- Excessive use of fertilizers destroys the useful microorganisms in the soil and it also upsets the composition of soil.
Question 3:
What are the indigenous methods adopted by the farmers in our county to reduce and control the changes in the nature of soil?
Solution :
The indigenous methods adopted by the farmers
- Quick lime is sprayed in the field to maintain the pH of the soil and increase the microbial activity.
- Azolla is a water plant which is allowed to grow in the paddy fields to increase the nitrogen content in the soil.
- The farmers use organic fertilizers and chemical fertilizers in proper concentration.
Question 4:
What are the aspects to be looked into when fertilizers are applied and when substances like lime are sprinkled in the soil? Discuss with friends and arrive at practical suggestions.
Solution :
- Care should be taken while applying fertilizers which should not destroy the organisms beneficial to the nature.
- The use of manures does not destroy the natural organic factors.
- One must know about the organic factors present in the soil before manuring.
- Alkaline fertilizers should be used in the excess acidic soil.
- If the soil is having too much of alkalinity fertilizers having acidic property should be used.