Chemistry MCQ Quiz - Objective Question with Answer for Chemistry - Download Free PDF

The correct answer is Limestone.

• Limestone is a form of calcium carbonate.
• Other Different forms of calcium carbonate are Chalk and Marble.
• Calcium carbonate is a chemical compound with the formula CaCO₃.
• It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone, which is a type of sedimentary rock consisting mainly of calcite) and is the main component of eggshells, snail shells, sea shells, and pearls.

Additional Information

Properties of Calcium Carbonate:

• Molar mass - 100.0869 g/mol.
• Odor - odorless.
• Appearance - Fine white powder; chalky taste.
• pH value - 9

The correct answer is Filtration.

Key Points

Filtration

• Filtration is a process used to separate solids from liquids or gases by using a filter medium that allows fluid to pass through but not solid. 
• Filtration can be mechanical-biological or physical. 
• It does not help in disinfecting water. 
• If you want to disinfect the water you can boil it or you can use alum for chlorine tablets. 

Boiling

• Boiling is used to kill pathogenic bacteria, viruses, and protozoa. 

Chlorination

• Chlorine kills a large variety of microbial waterborne pathogens.
• Chlorination is the process of adding chlorine to the water to disinfect it and kill pathogens. 
• Amount of chlorine required for water disinfection around 1-16 milligrams per litre of water.

Coagulation

• Alum acts as an electrolyte that helps in settling the suspended matter in water.
• The process of adding alum to disinfect water is called coagulation. 

The correct answer is Radon.

1. Radioactivity is a nuclear phenomenon in which an unstable nucleus undergoes decay and is referred to as radioactive decay.
2. Three types of radioactive decay occur in nature : (i) α-decay (ii) β-decay (iii) γ-decay
3. Noble Gases
   1. There are six elements in Group 18 of the Periodic Table - Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr) , Xenon (Xe) and Radon (Rn) which were earlier termed as inert gases or rare gases.
   2. Both of these terms are now no longer used as they are not so rare and not completely inactive. They do show some chemical reactivity in the form of some xenon and krypton compounds and hence are termed as noble gases.
   3. Occurrence
      1. All the noble gases except Radon occur in the atmosphere. Xenon and radon are the rarest elements of the group.
      2. Radon is a radioactive element. Radon (²²²Rn) is a decay product of Radium (²²⁶Ra) and is obtained by pumping off the gas from radium chloride solutions. 
      3. They are the minor constituent of the air, the atmospheric abundance being ~ 1% by volume of which argon is the major constituent. Ne, Ar, Xe and Kr are obtained by fractional distillation of liquid air.
      4. Helium and sometimes neon is found in minerals of radioactive origin e.g., pitchblende, monazite, cleveite. The main commercial source of helium is natural gas to an extent of 2-7%.
      5. They have closed valence shell electronic configuration due to which they have the least tendency to react.
      6. The best-characterised compounds are those of xenon with fluorine and oxygen only under certain conditions and only with highly electronegative fluorine and oxygen.
   4. Uses: These gases have several uses. Argon is used to provide an inert atmosphere, helium is used in filling balloons for meteorological observations, neon is used in discharge tubes and fluorescent bulbs.

The correct answer is Sulphide coating on silver.

• Silver does not react with oxygen as it is highly unreactive.

Key Points

• But over time its surface turns black due to exposure to the air.
• Due to the availability of Hydrogen Sulphide (H₂S) in the air, a layer of silver Sulphide (Ag₂S) is formed and silver loses its shine.
• This blackness can be minimized by covering it with polythene.
• This blackness is a temporary effect on the surface and can be removed by rubbing with a mild soap solution prepared in warm water. 

The correct answer is washing soda.

Key Points

• Uses of washing soda:
  • Sodium carbonate (washing soda) is used in glass, soap, and paper industries.
  • It is used in the manufacture of sodium compounds such as borax.
  • Sodium carbonate can be used as a cleaning agent for domestic purposes.
  • It is used for removing the permanent hardness of the water.
• The Washing Soda's chemical name is sodium carbonate (Na2CO3).

Additional Information

• Borax is a white crystalline solid of the chemical formula Na2B4O7.10H2O. On heating, it loses water of crystallization.
  • The molecular formula for Borax is- H20B4Na2O17
• It is used:
  • as an alkaline buffer in dyeing and bleaching processes
  • as a preservative
  • in the manufacture of optical and borosilicate glasses
  • as a flux, and
  • in making glazes for pottery and tiles

K2CO3 or potassium carbonate is known as pearl ash.

• Pearl ash, in ancient times, was created by baking potash in a kiln in order to remove impurities. The remaining fine, white powder was pearl ash.
• Potassium carbonate is an inorganic compound and a white salt which is soluble in water.
• It is mainly used in the production of glass and soap.

Additional Information

The correct answer is Sodium carbonate.

Explanation:

• Washing soda is a chemical compound with the formula Na₂CO₃, known as sodium carbonate, and it's a salt of carbonic acid.
• Properties of a Washing soda:
  • It is a transparent crystalline solid.
  • It is one of the few metal carbonates which are soluble in water.
  • It is alkaline with a pH level of 11, it turns red litmus to blue.
  • It has detergent properties or cleansing properties because it can remove dirt and grease from dirty clothes, etc.
  • It attacks dirt and grease to form water-soluble products, which are then washed away on rinsing with water. 

Important Points

Some common chemical compounds with their common names are:

The correct answer is Lactic Acid.

Key Points

• Lactic acid is present in Sour milk or curd.
• The sourness of the milk is due to the presence of lactic acid.
• Human beings feel tired due to the accumulation of lactic acid in the muscles.​

Additional Information

 Key Points

• Atomic Mass of the Hydrogen = 1
• Atomic Mass of the oxygen = 16

Explanation:

1 mole of hydrogen = 1gm

1 mole of oxygen = 16gm

Water (H2O) = 2 Hydrogen atoms + 1 Oxygen atom

2 mole of hydrogen = 2gm

1 mole of oxygen = 16 gm

The ratio of the mass of Hydrogen: Ratio of mass of Oxygen =  2/16 = 1/8 

The ratio of the mass of Hydrogen to the mass of Oxygen in water is always 1:8.

• The number of water molecules present is washing soda is 10.
• We know the molecular formula for Washing Soda is Na₂CO₃.10H₂O.
• Recrystallisation of Sodium Carbonate (Na₂CO₃) gives washing soda.
• In a Washing soda, water is present in the form of crystals.

The correct answer is Vermilion.

• Mercury Sulfide is also known as Vermilion.
• It is a chemical compound composed of the chemical elements mercury and sulfur.
• The chemical formula of Mercury sulfide is HgS.
• It is dimorphic with two crystal forms:
  • Red cinnabar
  • Black metacinnabar

Additional Information

• Marsh Gas is the common name of Methane with the formula of CH₄.
• Mohr's Salt is the common name of Ammonium Ferrous Sulphate with the formula of (NH₄)2Fe(SO₄)₂(H₂O)₆.
• Potash Alum is the common name of Potassium Aluminium Sulphate with the formula of KAl(SO₄)₂.

The correct answer is Double displacement reaction.

Concept:

Chemical reaction:

• It is a process in which one or more substances, the reactants, are converted to one or more different substances, the products.
• A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.

Explanation:

• Double displacement reaction: 

• It is a chemical reaction in which two compounds react and exchange their ions forming new products. 
• This reaction often results in the formation of an insoluble compound called a precipitate. 
• Such reactions are represented by equations of the following form: A⁺B^- + C⁺D^- → A⁺D^- + B^-C⁺

​In the given chemical reaction: 

NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)

The reactants NaCl and AgNO₃ have exchanged their ions to form NaNO3  and AgCl. 

Thus, it is an example of a double displacement reaction.^​

^{Additional Information}

Types of Chemical Reactions:

Combination reaction:

• Two or more elements or compounds combine together to form a single compound.
• Such reactions are represented by equations of the following form:     A + B → AB.

Decomposition reaction:

• The opposite of a combination reaction, a complex molecule breaks down to make simpler ones.
• Such reactions are represented by equations of the following form: AB → A + B.

Displacement reaction:

• One element takes place with another element in the compound.
• Such reactions are represented by equations of the following form: A + BC → AC + B.

Redox reaction:

• It is a reaction in which one species is reduced and the other is oxidized. 
• Reduction means losing Oxygen or gaining hydrogen 
• Oxidation means gaining oxygen or losing hydrogen. 

Explanation:

• Calcium hydroxide is sparingly soluble in water producing an alkaline solution known as limewater.
• Calcium Carbonate is a chemical compound found commonly in rocks as minerals and is the main component of pearls and the shells of marine organisms, eggs, etc.
• When carbon dioxide gas is passed through or over limewater, it turns milky due to the formation of calcium carbonate.
• In the chemical reaction it can be shown as :

\(\rm \underset{Lime\ water}{Ca (OH)_2} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{CaCO_3 \ (g)}\)Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" id="MathJax-Element-1-Frame" role="presentation" style="display: inline; position: relative;" tabindex="0">Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" role="presentation" style="display: inline; position: relative;" tabindex="0">Ca(OH)2

• However, when an excess of CO2 ​is passed through this solution, the milkiness disappears. This is due to the formation of calcium bicarbonate which is colorless and soluble in water.

Ca(OH)2Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate" role="presentation" style="display: inline; position: relative;" tabindex="0">​\(\rm \underset{Lime\ water}{Ca (OH)_2} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{CaCO_3 \ (g)}\)​\(\rm \underset{Lime\ water}{Ca CO_3} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{Ca(HCO_3)_2 \ (g)}\)Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate\(\rm \underset{Calcium\ Carbonate}{Ca CO_3} \ \ +H_2O+ \ \underset{Carbon \ Dioxide}{CO_2 \ (g) } \ \longrightarrow \ \underset{Calcium \ bi\ Carbonate}{Ca(HCO_3)_2 \ (g)}\)

Additional Information Reaction involved-

CaCO₃ + 2HCl →  CaCl₂ + CO₂ + H₂O

• The evolved gas is carbon dioxide which then passes through lime water and turns it milky.

Ca(OH)₂ + CO₂ → H₂O + CaCO₃  

• Due to formation of these compounds
• when excess CO₂ is passed

CaCO₃ + H₂O + CO₂ →  Ca(HCO₃)₂ 

• Bicarbonate is formed which again clears the solution

Mistake Points

•  Do not confuse Calcium carbonate and calcium bicarbonate.
• One produces white colour while the other makes it colourless.