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

The correct answer is Burning wood.

Key Points

• Burning wood is a chemical change because it involves the transformation of wood into new substances such as carbon dioxide, water vapor, ash, and heat energy.
• During burning, a chemical reaction known as combustion occurs, where wood reacts with oxygen to produce energy and byproducts.
• The process is irreversible, meaning the original wood cannot be recovered after burning, which is a hallmark of a chemical change.
• New chemical bonds are formed, and old bonds are broken during the process, indicating a change in the chemical composition of the material.
• Other examples of chemical changes include rusting of iron, cooking food, and souring of milk.

Additional Information

• Chemical Change: A process where one or more substances are transformed into new substances with different chemical properties. Examples include burning, rusting, and fermentation.
• Physical Change: A change in the state, shape, or size of a material without altering its chemical composition. Examples include melting ice, boiling water, and cutting paper.
• Combustion: A high-temperature exothermic reaction between a fuel (e.g., wood) and an oxidant (e.g., oxygen) that produces energy (heat and light) and byproducts like carbon dioxide and water.
• Irreversibility: Chemical changes are often irreversible, meaning the original substances cannot be restored. This is a key distinction from physical changes, which are usually reversible.
• Indicators of a Chemical Change: Common signs include color change, formation of a precipitate, emission of gas, change in temperature, and production of light or sound.

The correct answer is NH₄Cl.

Key Points

• NH₄Cl (Ammonium chloride) is a salt of a weak base (NH₃) and a strong acid (HCl), making its aqueous solution slightly acidic due to hydrolysis.
• In water, NH₄Cl dissociates into NH₄⁺ and Cl⁻ ions. The NH₄⁺ ion undergoes hydrolysis to form NH₃ and H⁺ ions, increasing the acidity.
• The Cl⁻ ion does not hydrolyze because it is the conjugate base of a strong acid (HCl) and remains inert in the solution.
• The pH of an NH₄Cl solution is typically less than 7, confirming its acidic nature.
• Other options like Na₂CO₃ and CH₃COONa are basic, while NH₄CH₃COO is nearly neutral due to the balance between its acidic and basic components.

Additional Information

• Hydrolysis: It is the reaction of a salt with water to form an acidic or basic solution depending on the strength of the parent acid and base.
• Ammonium Ion (NH₄⁺): It is a weak acid that hydrolyzes in water, releasing H⁺ ions and contributing to the solution's acidity.
• Conjugate Acid-Base Pair: NH₄⁺ is the conjugate acid of the weak base NH₃, while Cl⁻ is the conjugate base of the strong acid HCl.
• pH of Salts: The pH of a salt solution depends on the hydrolysis of its ions. Salts of strong acids and weak bases are acidic, while salts of strong bases and weak acids are basic.
• Non-Hydrolyzing Ions: Ions like Cl⁻, derived from strong acids, do not hydrolyze and do not affect the solution's pH.

The correct answer is Butter is separated from cream by the churning method..

Key Points

• Churning is a process that separates the butter from cream by using mechanical agitation.
• During churning, cream is beaten, and as a result, butter separates out from the liquid. The liquid part is known as buttermilk.
• In the churning method, butter floats to the top, while buttermilk stays at the bottom due to their different densities.
• The butter obtained from this method can be used for various purposes in cooking, while buttermilk is often consumed as a refreshing drink or used in cooking as well.
• The process of separating butter from cream has been traditionally used in dairy farming for centuries and is still used today in both small-scale and large-scale dairy production.

Additional Information

• Other methods of separating butter:
  • Modern butter-making: In modern butter-making factories, the churning process is carried out in large machines known as churners, which significantly speed up the process compared to manual methods.
  • Clarified Butter: Butter can also be heated to separate the milk solids, resulting in clarified butter, also known as ghee, which is used extensively in South Asian cooking.
• Benefits of consuming butter:
  • Butter is rich in essential fatty acids and fat-soluble vitamins such as Vitamin A, D, E, and K.
  • When consumed in moderation, butter can be part of a healthy diet, especially when used in place of trans fats found in margarine and processed oils.

The correct answer is Jam.

Key Points

• Sugar is commonly used in food processing and preservation, and one of its primary uses is in making jam.
• In the preparation of jam, sugar acts as both a sweetener and a preservative, allowing the jam to be stored for long periods without spoiling.
• Jam is made by cooking fruit with sugar, and in this process, sugar helps in the gel formation, which is essential for the jam to set properly.
• Jam can be made from various fruits, such as strawberries, raspberries, and mangoes, and sugar is the key ingredient that contributes to its flavor and texture.
• Besides jam, sugar is also used in a wide variety of other food products such as cakes, beverages, and candies, but in the context of this question, it is specifically linked to making jam.

Additional Information

• Preserving Food with Sugar
  • Sugar is widely used in the preservation of fruits and vegetables, particularly in the making of jams and jellies.
  • By helping fruits to release their pectin and sugars, sugar allows jams and jellies to thicken and set properly.
  • Along with being a preservative, sugar also enhances the natural flavors of the fruits used in jams.

The correct answer is two liquids.

Key Points

• An emulsion
  • It can be defined as a colloid consisting of two or more non-homogenous types of liquids wherein one of the liquids contains the dispersion of the different forms of liquids.
  • Emulsions are the mixtures of two or more types of liquids where, one is such as droplets, of tiny or even ultramicroscopic size, which are distributed throughout each other. Hence, Option 3 is correct.
  • These are usually formed from the component of liquids either in natural form or, more often, using mechanisms such as agitation, which is provided that these fluids mixed have no kind of mutual solubility.
  • Emulsions are said to be stabilized by some agents forming films at the surface of droplets or those which impart to them a kind of mechanical stability.
  • The unstable form of emulsions eventually separates into two forms of liquid layers.
  • The stable emulsions are destroyed by destroying or by deactivating the emulsifying agent—for example by the addition of appropriate third-party substances or even by the process of freezing or by heating.
  • Some common emulsions are milk (where the dispersion of fat molecules or droplets in the aqueous solution) and also butter (which is the dispersion of droplets of particles of an aqueous solution in the fat).

• Theories of Emulsification
  • Since there are different processes and mechanisms (both chemical and physical) involved in the process of emulsification, there are several theories that accompany it.
• Surface Tension Theory: This theory states or describes emulsification as a process that occurs by the reduction of interfacial tension between two phases.
• Repulsion Theory: With this theory, we learn that the emulsifying agent produces a film over one phase which further leads to the formation of globules. These compounds tend to repel each other and the repulsive force that exists between them helps them to remain suspended in the dispersion medium.

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:

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 increases.

Important Points

• In normal cases, the volume of substances increases on heating and decreases while cooling.
• When 1 litre of water is cooled from 4°C to 0°C volume of water will start increasing this due to water's unique property known as 'Anomalous Expansion of Water'.
• Anomalous Expansion of Water occurs between 4°C to 0°C.
• The density of water is a maximum at 4 °C.
• When water is cooled from 4°C to 0°C, its density decreases.
• The anomalous expansion of water helps preserve aquatic life during very cold weather.

Explanation:

• When water reaches 4°C the molecules have been pushed as close to one another as possible and the density of water becomes precisely 1.00 g/cm³
• When water freezes at 0°C due to the crystal structure the molecules arranged in some structured fashion so a little far apart ended up less dense - 0.93 g/cm³  - and so floats due to buoyancy.

As density decreases the volume increases.

Volume = mass /density.

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 :

">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">​​Lime water (aq) + CO2 (g)Carbon Dioxide ⟶ CaCO3 (g)Calcium Carbonate

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.

The correct answer is option 1, i.e  Alkali Metals.

EXPLANATION:

• The elements in the first group of s-block are also known as Alkali Metals. These have only one electron in their outermost shell and hence are quite reactive as they easily lose their electron to form bonds with non-metals.

• The elements in the second group of s-block are also known as Alkaline Earth Metals. These have two electrons in their outermost shell and are less reactive than Alkali metals.
• Halogens are the group 17 elements and are placed in the p-block.
• Noble gases are the group 18 elements and are placed in the p-block. These are the least reactive amongst all the elements found in the periodic table as they have a stable configuration.

The correct answer is Methanoic acid.

Key Points

• Nettle is an herbaceous plant that grows in the wild.
• Nettle leaves have stinging hair, which causes painful stings when touched accidentally. 
• This is due to the methanoic acid secreted by them. 
• A traditional remedy is rubbing the area with the leaf of the dock plant, which often grows beside the nettle.

Additional Information

• The word ‘atom’ is coined by Democritus.
• He suggested that if we go on dividing matter at a certain point the atom becomes indivisible or cannot be divided further.
• He called these particles as atoms (Indivisible).

 

Scientist	Discovered
Thomson	Electron
E Rutherford	Discovered alpha and beta particles
John Dalton	Father of Atomic Theory

The correct answer is The acid present in tomatoes.

Key Points

• Oxalic acid is a chemical compound that occurs naturally in almost every plant to some degree, including fruit, vegetable and grain plants. 
• Tomato contains more than 10 types of acids such as citric acid, malic acid, ascorbic acid, oxalic acid etc. 
• The oxalic acid content of tomatoes is about 50 mg per 100 g serving. 

Additional Information 

• Some natural sources of acid:

The correct answer is green.

Key Points 

• Barium Nitrate Ba(NO₃)₂ is an Oxidizer used to produce green colour in fireworks and fountains.
• This compound is also used in the production process of Barium Oxide in the vacuum tube industry.
• Barium is also used in medicine and oil and gas production.
• It is an inorganic compound that occurs with other elements like sulfur, oxygen, etc.
• Barium is found at 0.0425% on the earth’s crust, and 13 μg/L in seawater.
• It is a non-combustible compound but enhances the burning of combustible elements.
• The melting point of barium nitrate is 592 degrees Celcius.​

Additional Information

• 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.