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

Concept:

Vitamins:

• Vitamins are organic compounds that are present in minute amounts in natural foodstuffs.
• Most vitamins come from food because the body either does not produce them or produces very little.
• Vitamins are of two types.
  • Fat-soluble vitamins- Vitamins A, D, E, K.
  • Water-soluble vitamins- Vitamin C and all the B vitamins. 

• There are 13 vitamins - A, C, D, E, K, and B vitamins (thiamine, riboflavin, niacin, pantothenic acid, biotin, B6, B12, and folate), each of them have a different job.
• Vitamin A, D, E, K are Fat-Soluble vitamins and are stored in fat cells while vitamins B and C are water-soluble vitamins that are not stored in your body.
• The liver acts as a storage site for vitamin A, D, E, K, and B12 for the times when they may be lacking in the diet.
• Vitamin D acts as a hormone, produced by the kidneys it helps to control the concentration of calcium in the blood and is vital for the development of strong bones.
• Water-soluble vitamins like Thiamine, folate, biotin, riboflavin are synthesized by gut bacteria.

Explanation:

• Vitamin E is a mixture of four vitamins called α, β, γ and δ tocopherols among which α tocopherol is the most active.
• Characteristics:
  • Light yellow fat soluble in oils.
  • Stable to heat and oxidation.
• Sources are cotton seed oil, maize oil, peanut oil and wheat germ oil.
• Deficiency causes damage to the reproductive system.

Hence, Vitamin E is also called tocopherol.

Additional Information

• Riboflavin is vitamin B₂.
• Calciferol is vitamin D.
• Thiamine is vitamin B₁.

Explanation:

Enzyme catalysis:

⇒ Catalysis is a phenomenon in which the rate of the reaction is altered with the help of a substance called a catalyst (the catalyst does not participate in the reaction; its concentration and composition remain unchanged).

⇒ The substance used to change the rate of the reaction is called a catalyst. Enzymes are a class of catalysts that are responsible for facilitating and increasing the rate of many vital biochemical reactions in plants and animals.

The catalysis in which enzymes act as a catalyst is called enzyme catalysis.

• A single molecule of the enzyme catalyst can transform up to a million molecules of the reactant per second. Hence, enzyme catalysts are said to be highly efficient.
• These biochemical catalysts are unique to certain types of reactions, i.e. the same catalyst cannot be used in more than one reaction.
• The effectiveness of a catalyst is maximum at its optimum temperature. The activity of the biochemical catalysts declines at either side of the optimum temperature.
• Enzymes are mostly proteinous in nature. Enzymes are denatured by ultraviolet rays and at high temperatures.

The correct answer is option 2, i.e., The stability of +5 oxidation state decreases down the group.

• Out of the given options, the correct statement regarding the oxidation state of Group 15 elements (Nitrogen family) is the stability of +5 oxidation state decreases down the group.
• The stability of +5 oxidation state decreases down the group and that of +3 oxidation state increases, with BiF₅ being the only well-characterized Bi (V) compound. Hence, Option 1 is NOT correct while Option 2 is correct.
  • This is because of the 'inert-pair effect'. 
• Inert-pair effect is the tendency of the two s-electrons to not participate in bonding due to the high energy needed for unpairing them.
  • This phenomenon is seen in compounds of post-transition metals (Group 13, 14, 15, and 16).
• The tendency of -3 oxidation state decrease down the group.
• This happens due to the increase in size and metallic character of elements down the group.
• The last member of the Nitrogen family, Bismuth hardly forms any compound with -3 oxidation state.
• Nitrogen is restricted to maximum covalency of 4 because it has 4 orbitals (one s and three p) available for bonding.
• The most common oxidation states exhibited by the Group 15 elements is -3, +3, and +5.
• Nitrogen exhibits +1, +2, and +4 oxidation states also when it reacts with oxygen.
• Phosphorous exhibits +1 and +4 oxidation states in some oxoacids.

Concept:

Explanation:

• 2-acetoxybenzoic acid is commonly known as aspirin.
• It is prepared by the reaction of acetylation of salicylic acid. It can be achieved by the reaction of salicylic acid with acetic acid in presence of catalyst acids.
• However, the yield is low when acetic acid is used and it can be replaced by acetic anhydride which gives a comparatively much higher yield.
• The acetylation of the phenol group of salicylic acid occurs giving the product Acetylsalicylic acid commonly known as aspirin.
• The reaction is:

Explanation:

The position of d-block elements is in between s-block and p-block elements in the periodic table. These d-block elements are called transition elements because they exhibit transitional behaviour between s-block and p-block elements. 

• Transition metals are d-block elements with valence shell configuration ns² (n-1) d^(1-10) .
• The transition metals and their ions easily coordinate to a number of negative ions or neutral molecules having lone pairs of electrons to form complexes.
• The reason for this is small size and high nuclear charge of these metals and availability of vacant d-orbitals of suitable energy to accommodate lone pairs of electrons donated by the ligands.
• The cations of the d-block elements have a strong tendency to form complexes with certain molecules or ions called ligands. 

 So, Transition metals form complexes due to their Small size, Available d orbital and Large ionic charge.

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 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 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 :

\(\rm \underset{Lime\ water}{Ca (OH)_2} \ (aq) \ + \ \underset{Carbon \ Dioxide}{CO_2 \ (g) }\ \longrightarrow \ \underset{Calcium \ Carbonate}{CaCO_3 \ (g)}\)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.

• 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.

• Aluminium (Al) metal reacts with steam to form a metal oxide and hydrogen.
• This reaction can be given as

2Al + 3H₂O (g) → Al₂O₃ + 3H₂ (g)

• Other metals of this type are Iron (Fe) and Zinc (Zn).

• But these metals do not react with either hot or cold water.

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.