Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

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Tamilnadu Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

Samacheer Kalvi 9th Science Acids, Bases and Salts Textbook Exercises

I. Choose the correct answer.

Question 1.
Zn + 2HCl ➝ ZnCl2 + ………….. ↑
(a) H2
(b) O2
(c) CO2
Answer:
(a) H2

Question 2.
Apple contains malic acid. Orange contains ……………….
(a) citric acid
(b) ascorbic acid
Answer:
(b) ascorbic acid

Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

Question 3.
Acids in plants and animals are organic acids. Whereas Acids in rocks and minerals are ………………..
(a) Inorganic acids
(b) Weak acids
Answer:
(a) Inorganic acids

Question 4.
Acids turn blue litmus paper to …………………
(a) Green
(b) Red
(c) Orange
Answer:
(b) Red

Question 5.
Since metal carbonate and metal bicarbonate are basic they react with acids to give salt and water with the liberation of ………………
(a) NO2
(b) SO2
(c) CO2
Answer:
(c) CO2

Question 6.
The hydrated salt of copper sulphate has …………….. colour
(a) Red
(b) White
(c) Blue
Answer:
(c) Blue

II. Answer in brief.

Question 1.
Name any two metals which do not react with sodium hydroxide.
Answer:
Few metals do not react with sodium hydroxide. For example: Cu, Ag, Cr.

Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

Question 2.
Write any four uses of acids.

  • Sulphuric acid is called King of Chemicals because it is used in the preparation of many other compounds. It is used in car batteries also.
  • Hydrochloric acid is used as a cleansing agent in toilets.
  • Citric acid is used in the preparation of effervescent salts and as a food preservative.
  • Nitric acid is used in the manufacture of fertilizers, dyes, paints and drugs.

Question 3.
Give the significance of pH of soil in agriculture.
Answer:
In agriculture, the pH of soil is very important. Citrus fruits require slightly alkaline soil, while rice requires acidic soil and sugarcane requires neutral soil.

Question 4.
When does the acid rain occur?
Answer:
The pH of rain water is approximately 7 which means that it is neutral and also represents its high purity. If the atmospheric air is polluted with oxide gases of sulphur and nitrogen, they get dissolved in rainwater and make its pH less than 7. Thus, if the pH of rain water is less than 7, then it is called acid rain.

Question 5.
What are the uses of Plaster of Paris?
Answer:

  1. It is used for plastering bones
  2. It is used for making casts for statues.

Question 6.
Two adds ‘A’ and ‘B’ are given. Acid A gives one hydrogen ion per molecule of the acid in solution. Acid B gives two hydrogen ions per molecule of the acid in solution.

  1. Find out acid A and acid B.
  2. Which acid is called the King of Chemicals?

Answer:

  1. Acid A is HCl and Acid B is H2SO4
  2. Sulphuric acid is called the King of Chemicals.

Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

Question 7.
Define aquaregia.
Answer:
Metals like gold and silver are not reactive with either HCl or HNO3. But the mixture of these two acids can dissolve gold. This mixture is called Aquaregia. It is a mixture of hydrochloric acid and nitric acid prepared optimally in a molar ratio of 3:1. It is a yellow- orange fuming liquid. It is a highly corrosive liquid, able to attack gold and other resistant substances.

Question 8.
Correct the mistakes:

  1. Washing soda is used for making cakes and bread soft, spongy.
  2. Calcium sulphate hemihydrate is used in textile industry.

Answer:

  1. Baking soda is used for making cakes and bread soft, spongy.
  2. Calcium Oxychloride hemihydrate is used in textile industry.

Question 9.
What is neutralization reaction? Give an example.
Acids and bases neutralize each other to form corresponding salts and water.
Example: Bases react with acids to form salt and water.
KOH + HCl ➝ KCl + H2O
The above reaction between a base and an acid is known as Neutralisation reaction.

III. Answer in detail.

Question 1.
Why does distilled water not conduct electricity whereas rain water does?
Answer:
Distilled water is created through the process of distillation.

In this process, the pure water (H2O) is boiled to remove contaminants. This is done by the capturing of steam that rises after boiling of water followed by cooling. This is distilled water and is free of ions that are required for the conduction of electricity. Whereas, the pollutants present in the atmospheric air gets dissolved in rainwater which provides necessary ions for the conduction of electricity.

Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

Question 2.
Plaster of Paris should be stored in a moisture proof container. Why?
Answer:
The Plaster of Paris .should be stored in a moisture-proof container as it turns into a hard substance known as gypsum on absorption of water from moisture.

Question 3.
Write any four uses of bases.
Answer:

  1. Sodium hydroxide is used in the manufacture of soap.
  2. Calcium hydroxide is used in white washing of building.
  3. Magnesium hydroxide is used as a medicine for stomach disorder.
  4. Ammonium hydroxide is used to remove grease stains from cloths

Question 4.
Write any five uses of salts.
Answer:
Common Salt (NaCl): It is used in our daily food and used as a preservative.

  1. Washing Soda (Sodium Carbonate):
    • It is used in softening hard water.
    • It is used in glass, soap and paper industries.
  2. Baking Soda (Sodium bicarbonate -NaHC03):
    • It is used in making of baking powder which is a mixture of baking soda and tartaric acid.
    • It is used in soda-acid fire extinguishers.
    • Baking powder is used to make cakes and bread, soft and spongy.
    • It neutralizes excess acid in the stomach and provides relief.
  3. Bleaching powder (Calcium Oxychloride – CaOCl2)
    • It is used as disinfectant.
    • It is used in textile industry for bleaching cotton and linen.
  4. Plaster of Paris (Calcium Sulphate Hemihydrate – CaS04 . \(\frac { 1 }{ 2 }\)H20)
    • It is used for plastering bones
    • It is used for making casts for statues

Question 5.
Sulphuric acid is called King of Chemicals. Why is it called so?
Answer:
Sulphuric acid is called King of Chemicals because it is used in the preparation of many Other compounds. It is used in car batteries also.
Acids react with metallic oxides to give salt and water.
CaO + H2S04 CaS04 + H20

Activity

Question 1.
Take about 10 ml of dilute hydrochloric acid in a test tube and add a few pieces of zinc granules into it. What do you observe? Why are bubbles formed in the solution?
Answer:
Take a burning candle near a bubble containing hydrogen gas, the flame goes off with a ‘Popping’ sound. This confirms that metal displaces hydrogen gas from the dilute acid.
Bubbles are formed as Zinc reacts with HCl to form ZnCl and Hydrogen gas is released.

Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

Question 2.

  • Take solutions of hydrochloric acid or sulphuric acid.
  • Fix two nails on a cork and place the cork in a 100 ml beaker.
  • Connect the nails to the two terminals of a 6V battery through a bulb and a switch as shown in Figure.
  • Now pour some dilute HCl in the beaker and switch on the current.
  • Repeat the activity with dilute sulphuric acid, glucose and alcohol solutions. What do you observe now?
  • Does the bulb glow in all cases?

Answer:
The bulb glows when the solution in the beaker is hydrochloric acid or sulphuric acid as they ionise into H+ ions thus facilitating the flow of current.
Both hydrochloric acid and sulphuric acid readily ionise to H+, Cl and 2H+ and SO4- in solution and thus conduct electricity letting the bulb glow. Whereas glucose and alcohol do not ionise and hence the bulb doesn’t glow.

Question 3.
Collect the following samples from the science laboratory – Hydrochloric acid, sulphuric acid and Nitric acid, Sodium hydroxide, Potassium hydroxide. Take 2 ml of each solution in a test tube and test with a litmus paper and indicators phenolphthalein and Methyl orange. Tabulate your observations.

Sample Solutions Litmus Paper Indicators
Blue Red Phenolphthalein Methyl Orange
Hydrochloric acid Colourless Pink
Sulphuric acid Colourless Pink
Nitric acid Colourless Pink
Sodium hydroxide Pink Yellow
Potassium hydroxide Pink Yellow

Question 4.
Fill in the blanks in the following table based on the concept of water of crystallisation.

Salt Formula of an hydrous salt Formula of hydrated salt Name of hydrated salt
Zinc sulphate ZnSO4 ZnSO4.7H2O
Magnesium chloride MgCl2 Magnesium chloride hexahydrate
Iron (II) sulphate FeSO4.7H20 Iron (II) sulphate heptahydrate
Calcium chloride CaCl2 CaCl2.2H2O
Sodium thiosulphate Na2S2O3 Sodium thiosulphate pentahydrate

Answer:

Salt Formula of an hydrous salt Formula of hydrated salt Name of hydrated salt
Zinc sulphate ZnSO4 ZnSO4.7H2O Zinc sulphate heptahydrate
Magnesium chloride MgCl2 MgCl2. 6H2O Magnesium chloride hexahydrate
Iron (II) sulphate FeSO4 FeSO4.7H20 Iron (II) sulphate heptahydrate
Calcium chloride CaCl2 CaCl2.2H2O Calcium chloride dihydrate
Sodium thiosulphate Na2S2O3 Na2S2O3.5H2O Sodium thiosulphate pentahydrate

Question 5.
Boil about 100 ml of ground water in a vessel to dryness. After all the water get evaporated observe the inner wall of the vessel. Can you observe any deposits?
Answer:
Yes, this is the deposit of dissolved salts present in water.

Samacheer Kalvi 9th Science Acids, Bases and Salts Additional Questions

I. Short answers questions.

Question 1.
What are acids?
Answer:
Acids are those with chemical properties that includes; turning litmus red, neutralizing alkalis, and dissolving some metals; typically, a corrosive or sour-tasting liquid present in curd, fruit juices, vinegar, etc. The word ‘acid’ is derived from the Latin name “acidus” which means sour taste.

Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

Question 2.
Why is the term basicity is used for acids?
Answer:
The term basicity is used for acids since they have replaceable hydrogen atoms in a molecule.

Question 3.
What are bases?
Answer:
According to Arrhenius theory, bases are substances that ionise in water to form hydroxyl ions (OH). Bases that are soluble in water are called alkalis.

Question 4.
“All alkalis are bases, but not all bases are alkalis”. Justify this statement.
Answer:
Bases react with acids to neutralise them. Some are insoluble. Soluble bases are called Alkalis. For example CuO (copper oxide) does not dissolve in water, therefore it’s a base. Generally hydroxides of alkali metals and alkaline earth metals are called alkalis.

Question 5.
What is the correct procedure of mixing an acid and water? Why?
Answer:
One has to be cautious while mixing’a concentrated inorganic acid with water. Always the acid must be added to water gently. While adding acid to water, one has to keep stirring the mixture simultaneously. Water should never be added to an acid as it generates huge amount of heat and the mixture can splash out of the container and cause harm to the person handling it, causing bums.

Question 6.
“All acids contain one or more hydrogen atoms, but not all substances containing hydrogen are acids.” Support this statement with examples.
Answer:
HCl (hydrochloric acid), H2SO4 (sulphuric acid) and HNO3 (Nitric acid) are all examples of inorganic acids. They all have the hydrogen atom in common. Most acids essentially contain one or more hydrogen atoms. Whereas water (H20) also contains hydrogen, but it is not an acid. Similarly molecule of methane and ammonia also contain hydrogen, but all these do not produce H+ ions in aqueous solutions. Therefore it can be said that “all acids contain hydrogen, but all substances containing hydrogen are not acids.”

Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

Question 7.
Explain the role of pH in our digestive system.
Answer:
The pH of saliva is usually between 6.5 – 7.5.
pH of stomach fluid is approximately 2.0. This is because it produces hydrochloric acid which helps in the digestion of food without harming the stomach. pH in the small and large intestine ranges from 4.0 to 7.0.

II. Long answers questions.

Question 1.
Explain water of crystallisation.
Answer:
Many salts are found as crystals with water molecules they contain. These water molecules are known as water of crystallisation. Salts that contain water of crystallisation are called ‘ hydrated salts. The number of molecules of water hydrated to a salt is indicated after the dot in its chemical formula. For example, copper sulphate crystal have five molecules of water for each molecule of copper sulphate. It is written as CuS04.5H20 and named as copper sulphate pentahydrate. This water of crystallisation makes the copper sulphate blue.

When it is heated, it loses its water molecules and becomes white. Salts that do not contain water of crystallisation is called anhydrous salt.

Question 2.
What are four types of salts?
Answer:
Types of Salts

  1. Normal Salts
    A normal salt is obtained by complete neutralization of an acid by a base.
    NaOH + HCl ➝ NaCl + H2O
  2. Acid Salts
    It is derived from the partial replacement of hydrogen ions of an acid by a metal. When a calculated amount of a base is added to a polybasic acid, acid salt is obtained.
    NaOH + H2S02 ➝ NaHS04 + H20
  3. Basic Salts
    Basic salts are formed by the partial replacement of hydroxide ions of a diacidic or triacidic base with an acid radical.
    Pb(OH)2 + HCl ➝ Pb(OH)Cl + H2O
  4. Double Salts
    Double salts are formed by the combination of the saturated solution of two simple salts in equimolar ratio followed by crystallization. For example, Potash alum is a mixture of potassium sulphate and aluminium sulphate.
    KAI(SO4)2·12H2O

Question 3.
Classify acids based on their sources and basicity.
Answer:
Acids are classified in different ways as follows:
Based on their sources:

  1. Organic acids: Acids present in plants and animals (living things) are organic acids. Example: HCOOH, CH3COOH
  2. Inorganic acids: Acids prepared from rocks and minerals are inorganic acids or mineral acids. Example: HCl, HNO3, H2SO4

Based on their Basicity:

  1. Monobasic Acid: Acid that contain only one replaceable hydrogen atom per molecule is called monobasic acid. It gives one hydrogen ion per molecule of the acid in solution. Example: HCl, HNO3
  2. Dibasic Acid: An acid which gives two hydrogen ions per molecule of the acid in solution. Example: H3SO4, H2CO3
  3. Tribasic Acid: An acid which gives three hydrogen ions per molecule of the acid in solution. Example: H3P04

Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

Question 4.
Name the acid present in the given table.
Answer:
Acid and its source

SOURCE ACID PRESENT
Apple Malic acid
Lemon Citric acid
Grape Tartaric acid
Tomato Oxalic acid
Vinegar Acetic acid
Curd Lactic acid
Orange Ascorbic acid
Tea Tannic acid
Ant, Bee Formic acid
Stomach juice Hydrochloric acid

Question 5.
Describe the tests used to determine acids and bases.
Answer:
Take 10 ml of solution in a test tube and test with a litmus paper or indicators like phenolphthalein and methyl orange.

  1. Test with a litmus paper: An acid turns blue litmus paper into red. A base turns red litmus paper into blue.
  2. Test with an indicator Phenolphthalein: In acid medium, phenolphthalein is colourless.
    In basic medium, phenolphthalein is pink in colour.
  3. Test with an indicator Methyl orange: In acid medium, methyl orange is pink in colour. In basic medium, methyl orange is yellow in colour.

Samacheer Kalvi 9th Science Solutions Chapter 14 Acids, Bases and Salts

Question 6.
Differentiate between Acids and Bases.
Answer:

Acids Bases
Acids are proton donors or electron acceptors Bases are proton acceptor or electron donors
Acids are able to increase the H<sup>+</sup> ion concentration in aqueous solution. Bases are able to increase the OH” ion concentration in an aqueous solution
Acids have a pH value < 7. Bases have a pH value > 7.
Acids turn blue litmus paper red. Bases turn red litmus paper blue.
Acids react with bases to form salts in an aqueous medium. Bases react with acids to form salts.
Acids are sour to taste. Bases are soapy to touch.

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