Materials used in Daily life : Class 8

 

Materials used in Daily life

Tick mark the correct answer.

1.      Which of the following is acid?

a) HNO₃                                 b) Na₂CO₃                  

c) Ca(OH)₂                             d) NaCl

2.      What are the products formed by the reaction between acid and base?

a) Salt                                     b) Water and Hydrogen

c) Salt and water                   d) Salt and Hydrogen

3.      What is used by human to remove hyperacidity of stomach?

a) Mg(OH)₂                            b) NaOH

c) KOH                                    d) NH₄OH

4.      Which of  the following is acidic salt?

a) Nacl                                   b) Na2CO3

c) NH4Cl                                 d) K2SO4

5.      Which of the following brings temporary hardness of water?

a) Calcium Sulphate               b) Magnesium Chloride

c) Magnesium bicarbonate   d) Sodium bicarbonate

6.      Which of the following brings permanent hardness of water?

a) Calcium bicarbonate         b) Magnesium Chloride

c) Magnesium bicarbonate   d) Sodium bicarbonate

7.      Which of the following compound is formed after heating temporary hard water?

a) Calcium sulphate               b) Calcium chloride

c) Calcium carbonate            d) Calcium bicarbonate

8.      What is called for the homogeneous mixture of copper and tin?

a) Steel                                   b) Brass

c) Bronze                                d) Duralumin

9.      In which of the following method, zeolite is used to remove hardness of water?

a) permutit method                           b) Clark method

c) Boiling                                            d) Using washing soda

10.  Which of the following is not the effect of acid rain?

a) reduces the quality of soil            

b) the forest is destroyed

c) destroy the temples of archeological importance

d) beneficial for aquatic animals.

11.  Which of the following turns red litmus to blue?

a) water                                             b) Acid

c) Base                                               d) Salt

Answers:

    1.      (a) HNO₃ → Nitric acid is an acid.

    2.      (c) Salt and water → Acid + Base → Salt + Water (Neutralization reaction).

    3.      (a) Mg(OH)₂ → Magnesium hydroxide (Milk of magnesia) is used as an antacid.

    4.      (c) NH₄Cl → Ammonium chloride is an acidic salt.

    5.      (c) Magnesium bicarbonate → Causes temporary hardness.

    6.      (b) Magnesium chloride → Causes permanent hardness.

    7.      (c) Calcium carbonate → Forms when temporary hard water is heated.

    8.      (c) Bronze → Alloy of copper and tin.

    9.      (a) Permutit method → Uses zeolite to remove hardness.

    10.  (d) Beneficial for aquatic animals → Acid rain is harmful, not beneficial.

    11.  (c) Base → Turns red litmus blue.

    12.  (a) Copper and Zinc → Forms brass.

    13.  (a) Steel → Carbon + Iron = Steel.

Very Short answer questions:

1.      What is acid?

→ Acid is a substance that releases hydrogen ions (H⁺) in an aqueous solution and has a pH of less than 7.

2.      Write the use of Carbonic acid.

→ Carbonic acid (H₂CO₃) is used in soft drinks, carbonated beverages, and as a mild acid in some cleaning products.

3.      What is indicator?

→ An indicator is a substance that changes color in the presence of an acid or a base, helping to determine the pH of a solution.

4.      What is hardness of water?

→ Hardness of water is the presence of dissolved minerals like calcium and magnesium, which prevent soap from lathering easily.

5.      Write any one application of hydrochloric acid.

→ Hydrochloric acid (HCl) is used in the digestion process in the human stomach to break down food.

6.      What is salt?

→ Salt is a chemical compound formed by the reaction of an acid and a base, typically composed of positive and negative ions.

7.      What is acid rain?

→ Acid rain is rainwater that contains acidic pollutants, mainly sulfuric acid (H₂SO₄) and nitric acid (HNO₃), formed due to industrial emissions.

8.      What is mixed metal?

→ A mixed metal, or alloy, is a combination of two or more metals or a metal and a non-metal to enhance properties like strength and resistance to corrosion.

9.      Which metal mixture forms brass?

→ Brass is an alloy made of copper (Cu) and zinc (Zn).

10.  Write the name of any one acid found in acid rain.

→ Sulfuric acid (H₂SO₄) or Nitric acid (HNO₃).

11.  What is a base?

→ A base is a substance that releases hydroxide ions (OH⁻) in an aqueous solution and has a pH greater than 7.12.  What is basic salt?

→ A basic salt is a salt that contains a hydroxide (OH⁻) group or reacts with water to form a basic solution.

13.  In which color does methyl orange change in base?

→ Methyl orange changes to yellow in a basic solution.

Rama won a bronze medal in a competition. Which metals are mixed to make the medal she received?

→ Bronze is an alloy of copper (Cu) and tin (Sn).

Short Answer Questions:

    1.      Write two differences between hard water and Soft water.

Differences between hard and soft water:

• Hard water contains dissolved minerals like calcium and magnesium; soft water does not.
• Hard water forms less lather with soap, while soft water forms more lather.

    2.      Distinguish between base and alkali in two points.

·  A base is any substance that neutralizes an acid, while an alkali is a base that dissolves in water.

·  Not all bases are soluble in water, but all alkalis are bases.

    3.      Why does foam of soap is less in well water? Give reason.

Well water contains dissolved calcium and magnesium ions, which react with soap to form insoluble scum, reducing foam formation.

    4.      Write about the chemical which can bring the permanent hardness of water.

Permanent hardness of water is caused by the dissolved Chloride and sulphate salts of calcium and magnesium.

    5.      Which salt is formed by the reaction between hydrochloric acid and sodium hydroxide? Write with chemical equation.

Sodium chloride (NaCl) is the salt formed by the reaction between hydrochloric acid and sodium hydroxide.

Chemical equation: HCl + NaOH → NaCl + H₂O

    6.      Temporary hardness of water can be removed by boiling, why?

Temporary hardness of water can be removed by boiling because boiling precipitates calcium and magnesium bicarbonates as insoluble carbonates, removing hardness.

    7.      Write any two points of differences between temporary hardness of water and permanent hardness of water.

Differences between temporary and permanent hardness:

• Temporary hardness is due to bicarbonates, while permanent hardness is due to sulfates and chlorides.
• Temporary hardness can be removed by boiling, but permanent hardness requires chemical treatment.

    8.      Write any two chemical properties of base.

Two chemical properties of base are:

a) Base react with acid to form salt and water.

NaOH + HCl à NaCl + H₂O

(base)     (acid)   (salt)  (water)

b) Base react with ammonium salts to form ammonia gas.

NaOH + NH4Cl à                    NaCl + H2O + NH3

(Base)  (ammonium salt                                  (ammonia)

    9.      Write two differences between acid and base.

Two differences between acid and base are:

Acid	Base
Acids are generally sour in taste.	Bases are generally bitter in taste.
Acids turn blue litmus paper into red.	Bases turn red litmus paper into blue.

 

    10.  Write any one method to remove temporary hardness of water.

Temporary hardness of water is removed by boiling. Temporary hardness of water is due to the presence of soluble bicarbonates of calcium and magnesium. When boiled, they get changed into insoluble carbonates removing the temporary hardness.

Ca(HCO₃)₂ à CaCO₃ + H₂O + CO₂

    11.  We take medicine having aluminium hydroxide when we suffer from gastritis. Why?

We take medicine having aluminium hydroxide when we suffer from gastritis because aluminium hydroxide is a base which neutralizes excess stomach acid, reducing acidity and relieving discomfort.

    12.  How can we identify whether the given water is hard or not?

If water forms less lather with soap and leaves white deposits in kettles or pipes then such water is hard water.

    13.  Name any two bases with molecular formula.

Two bases with molecular formulas: are Sodium hydroxide (NaOH) and Calcium hydroxide (Ca(OH)₂

    14.  Define acidic salt with one example.

A salt formed by the reaction between a strong acid and weak base or a salt formed by the partial displacement of hydrogen of acid by a base is called acidic salt. For example: Sodium bisulphate (NaHSO₄), Copper sulphate (CuSO₄)

    15.  Write any two differences between organic acid and inorganic acid.

Two differences between organic and inorganic acid are:

Organic acids	Inorganic acids
They are obtained from organism and contains carbon in them.	They are obtained from mineral and may not contain carbon.
Organic acid are generally weak.	Inorganic acids are generally strong.

    16.  Write any two differences between strong acid and weak acid.

Strong acids get completely ionize in water.	Weak acids feebly ionize in water.
Most of the mineral acids like suphuric acid, hydrochloric acid are strong acid.	Most of the organic acid like citric acid, ascorbic acid etc. are weak acids.

 

    17.  Generally, rain water is acidic, why?

Rain water absorbs carbon dioxide present in the atmosphere and form carbonic acid. So, rain water is generally acidic in nature.

    18.  Ammonium Chloride is acidic salt, why?

Ammonium Chloride is acidic salt because It is formed from a strong acid (HCl) and a weak base (NH₃), making it acidic in solution.

    19.  Both lemon juice and sulphuric acid are acids, sulphuric acid corrodes cloth but lemon does not, why?

Sulfuric acid is a strong acid that dehydrates and corrodes fabrics, while citric acid in lemon juice is weak acid and it cannot dehydrates fabrics.

    20.  Gastritis patients are cured by consuming magnesium hydroxide, why?

Gastritis patients are cured by consuming magnesium hydroxide because t neutralizes stomach acid and acts as an antacid.

    21.  Write down any sources of each of the following acids.

a) Citric acid                b) Lactic acid

    Citric acid: Citrus fruits (e.g., lemon, orange)

Lactic acid: Milk and dairy products

    22.  Write any two differences between pure metal and alloy.

Pure Metal	Alloy
Pure metals are single elements.	Alloys are mixtures of metals.
Most of the pure metals are not very strong and corrosion resistant.	Alloys are stronger and more corrosion-resistant

 

    23.  Write any two differences between steel and stainless steel.

Steel	Stainless Steel
Steel contains iron and carbon	stainless steel has iron, carbon and chromium for rust resistance
Steel is less corrosion resistant.	Stainless steel is more corrosion-resistant

 

    24.  Show in a table the reaction of an acid with indicator.

Indicator	Acid reaction
Litmus paper	Turns blue to red
Methyl orange	Turns orange to red
Phenolphthalein	Colorless

    25.  Make a table to show the reaction of a base with indicators.

Indicator	Base Reaction
Litmus paper	Turns red to blue
Methyl orange	Turns yellow
Phenolphthalein	Turns pink

    26.  Make a table to show the reaction of salts with indicators.

Indicator	| Neutral Salt	| Basic Salt	Acidic Salt
Litmus paper	| No change	Turns blue to red	Turns red to blue
Methyl orange	No change	Turns red	| Turns yellow

    27.  What can be done to prevent acid rain?

The following are the preventive measures of acid rain.

a)      Reduce fossil fuel use and emissions.

b)      Use alternative energy sources like solar and wind.

    28.  Riya always washes her clothes in tubewell water. White clothes become dull instead of shiny. What is the reason for this dullness of white clothes? What do you suggest to her to solve this problem?

   Riya’s clothes dull in tube well water because hard water reacts with soap, forming insoluble scum that deposits on clothes. We would like to suggest her to use water softening agent or washing soda.

    29.  What are the causes for the increasing popularity of alloys? Prepare a list in two points.

The causes of increasing popularity of alloys are as follows:

a) Alloys are stronger and more durable.

b) They are more corrosion-resistant than pure metals.

    30.  How do you know that the acid rain is harmful? Give answer in two points.

Acid rain damages to the environment because it lowers the pH of soil and water bodies, harming plants, aquatic life, and microorganisms.

Acid rain reacts with metals, limestone, and marble, causing corrosion and deterioration of historical monuments, bridges, and buildings.

 

    31.  Roshan took out water from the well to wash his school uniform on Saturday. Sufficient lather is not produced while applying soap to it. What would you suggest to produce sufficient lather even in well water? Write with reason.

I would suggest Roshan the following points to produce sufficient lather.

• Boil water and then wash clothes. This removes the temporary hardness.
• Use a water softener like sodium carbonate or detergents.

Long Answer Questions.

    1.      What is acid? Write any two application of sulphuric acid. Write down the molecular formula of sodium hydroxide.

Acid is a substance that releases hydrogen ions (H⁺) when dissolved in water. It has a sour taste and turns blue litmus paper red.

Two applications of sulphuric acid (H₂SO₄):

i)         It is used in car batteries.

ii)       It is used in the production of fertilizers like ammonium sulfate.

Molecular formula of sodium hydroxide: NaOH

    2.      What is hard water? How could we remove permanent hardness of water? Describe any one method.

Hard water is water that contains a high concentration of dissolved calcium (Ca⁺⁺) and magnesium (Mg⁺⁺) ions.

We can remove permanent hardness of water by the  methods like the ion exchange method (permutit method) or using washing soda (sodium carbonate, Na₂CO₃).

a) One method – Using washing soda: When washing soda (Na₂CO₃) is added to hard water, it reacts with calcium and magnesium ions to form insoluble carbonates, which remove the hardness.
Reaction:

CaCl₂+Na₂CO₃→CaCO₃↓+2NaCl

MgSO₄+Na₂CO₃→MgCO₃↓+Na₂SO₄

    3.      Which acids are found in lemon and milk? Give any two properties of base.

Acid found in lemon and milk are citric acid and lactic acid respectively. Two properties of bases are:

a)      Bases taste bitter and feel slippery.

b)      They turn red litmus paper blue.

4.      Give any three examples of acids which are synthesized in laboratory. What changes are seen to the methyl orange in acid, base and salt? Show with chart.

Three laboratory-synthesized acids:

1. Hydrochloric acid (HCl)
2. Sulphuric acid (H₂SO₄)
3. Nitric acid (HNO₃)

Effect of methyl orange in different substances:

Substance	Color change in methyl orange
Acid	Red
Base	Yellow
Neutral (Salt)	Orange

 

    5.      All alkali are bases but all the bases are not alkalis, why? Give two examples of salts.

• Alkalis are bases that dissolve in water to release OH⁻ ions (e.g., NaOH, KOH). Bases include both soluble and insoluble substances that react with acids to form salts and water.
• Example: Aluminium hydroxide (Al(OH)₃) is a base but not an alkali because it is not soluble in water.

Two examples of salts:

1. Sodium chloride (NaCl)
2. Calcium carbonate (CaCO₃)

 

    6.      What is salt? Name any two salts used in our daily life. Why do we use litmus paper?

A salt is a compound formed when an acid reacts with a base, and the hydrogen ions of the acid are replaced by metal ions.

Two examples of salts:  Sodium chloride (NaCl) Calcium carbonate (CaCO₃)

We use litmus paper to find whether a given solution is acidic, alkaline or neutral. A blue litmus changes to red in acid, a red litmus changes to blue in alkaline while litmus paper remains unchanged in neutral solution.

    7.      What are the uses of following chemicals? Write.

Sodium bicarbonate, Magnesium sulphate, Ammonium hydroxide, Acetic acid.

Baking soda (NaHCO₃) – Used in cooking and baking

Magnesium sulphate i(MgSO₄) s used as fertilizer and to treat eclampsia

Ammonium Hydroxide (NH₄OH): It is used remove stain and grease.

Acetic acid (CH₃COOH): It is used for pickling and preservative.

    8.      Explain the method of removing temporary hardness of water with chemical reaction.

Temporary hardness is caused by dissolved bicarbonates (Ca(HCO₃)₂, Mg(HCO₃)₂) and can be removed by boiling.

Reaction:

Ca(HCO₃)₂→CaCO₃↓+CO₂+H₂O

Ca(HCO₃)₂ → CaCO₃ ↓ + CO₂ + H₂O

Ca(HCO₃​)₂​→CaCO₃​↓+CO₂​+H₂​O

    9.      What is meant by indicators? What happens in the following conditions?

Indicators are substances that change color when added to an acidic or basic solution.

i) A base reacts with an acid. Give one example of such chemical reaction.

When a base reacts with acid, it forms salt and water.

NaOH + HCl→NaCl + H₂O

 

    10.  Define acid with an example. If you are given a piece of blue litmus paper, how do you identify whether the liquid present in the bottle of kitchen is acid or water.

An acid is a substance that donates H⁺ ions in a solution.

Example: Hydrochloric acid (HCl).

If we are given a piece of blue litmus paper to determine whether the liquid present in the kitchen is acid or water by the following ways.

i) Blue litmus paper is dipped in the liquid.

ii) If its colour changed to red, it is acid and if its colour remain unchanged it is water.

    11.  Write any two causes of acid rain and mention its two effects.

Two Causes and effects of acid rain are:

a) Burning fossil fuels releases sulfur dioxide (SO₂) and nitrogen oxides (NO₂).

b) Industrial emissions and vehicle exhaust.

Two effects of acid rain are:

a) Damages crops, forests, and aquatic life.

b) Corrodes buildings and monuments.

    12.  How can we remove permanent hardness of water by permutit method? Explain with diagram.

We can remove permanent hardness of water by permutit medthod by the following ways:

a) Water is passed through a column containing Permutit (sodium aluminosilicate, Na₂Al₂Si₂O₈·xH₂O).

b) Ca²⁺ and Mg²⁺ ions in hard water are exchanged with Na⁺ ions, making the water soft.

Reaction:

CaCl₂ + Na₂Al₂Si₂O₈ → CaAl₂Si₂O₈ + 2NaCl

 

    13.  Write any two chemical properties of acid with balanced chemical reaction.

Two chemical properties of acids with reactions

Acids react with metals to produce hydrogen gas.

Zn + 2HCl → ZnCl₂ + H₂ ↑

 Acids react with bases to form salt and water.

H₂SO₄ + NaOH → Na₂SO₄ + H₂O

14.  Write any two chemical properties of base with balanced chemical equation.

Two chemical properties of bases with balanced chemical equations:
a) Reaction with acids (Neutralization reaction):

NaOH+HCl→NaCl+H₂O

 Reaction with ammonium salts to release ammonia gas:

NaOH+NH₄Cl→NaCl+NH₃+H₂O

    15.  Write the following chemical changes into balanced chemical equations.

a) alkali + Ammonium salt à Salt + Gas + water

. NaOH+NH₄Cl→NaCl+NH₃+H₂O

b) Acid  + base à Salt + water

    HCl+NaOH→NaCl+H₂O

    16.  How does acid rain occur? Write with chemical equation. Present two suggestions to minimize the effect of acid rain occurred in Nepal.

Acid rain occurs when pollutants like sulfur dioxide (SO₂​) and nitrogen oxides (NOx​) react with water vapor in the atmosphere to form sulfuric acid (H₂SO₄ ​) and nitric acid (HNO₃​), which fall as acid rain.

Chemical equations:

Formation of sulfuric acid: SO₂+2O₂→2SO₃

3SO₃+3H₂O ​→ 3H₂SO₄

Formation of nitric acid: 3NO₂​+H₂​O→HNO₃​

Suggestions to minimize acid rain in Nepal:

a) Use cleaner energy sources like hydroelectricity instead of fossil fuels.

b) Implement strict regulations to control emissions from industries and vehicles.

    17.  Which metals are mixed in the following alloys? present in table.

a) Steel            b) Brass           c) Stainless steel          d) Bronze

Alloy	Metals Present
Steel	Iron (Fe) and Carbon (C)
Brass	Copper (Cu) and Zinc (Zn)
Stainless Steel	Iron (Fe), Chromium (Cr), and Nickel (Ni)
Bronze	Copper (Cu) and Tin (Sn)

 

    18.  Complete the following table. Write down the molecular formula of nitric acid and calcium sulphate.

indicator	Change in colour
	Acid	Base
Phenolphthalein
Methyl orange

Ans:

Indicator	Change in Colour
	Acid	Base
Phenolphthalein	Colourless	Pink
Methyl orange	Red	Yellow

Molecular formula of: Nitric acid: HNO3\text{HNO}_3HNO3​Calcium sulfate: CaSO4\text{CaSO}_4CaSO4

    19.  Ram wants to wash clothe in pond water but the soap does not produce lather easily. What type of water is this? If this water contains the bicarbonates salts of calcium and magnesium then what kind of hardness such water contain? Suggest a method of removal of such hardness of water. How does the hardness of water removed by this method? Explain.

Ram is trying to wash clothes in hard water, which does not form lather easily with soap. Since the water contains bicarbonates of calcium and magnesium, it has temporary hardness.

Method to remove temporary hardness:

• Boiling: Boiling precipitates calcium and magnesium as insoluble carbonates.

Reaction:

Ca(HCO₃)₂→CaCO₃↓+CO₂+H₂O

 

    20.  Results obtained by reacting two samples with different indicators are shown in the table given below:

Samples	Methyl orange	Litmus paper	Phenolphthalein
Sample A	Red	Red	X
Sample B	Y	Blue	Pink

a) Which colour do X and Y represent?

X = Colourless (Phenolphthalein is colourless in acid.)

Y = Yellow (Methyl orange turns yellow in base.)

 

b) Among A and B, which will produce carbon dioxide gas when reacts with calcium carbonate?

Sample A is acidic (because methyl orange is red and litmus is red).

Acids react with calcium carbonate to produce CO₂ gas, so Sample A will produce CO₂ gas.

c) Given an example of sample A and Sample B with molecular formula.

 Examples with molecular formula:

Sample A (Acid example): Hydrochloric acid (HCl)

Sample B (Base example): Sodium hydroxide (NaOH)