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

The correct answer is Water.

pH of water is 7.

Key Points

• The pH of water is likely to be 7.
• pH is a measure of how acidic/basic water is.

Important Points

• The range goes:-
  • from 0 to 14, with 7 being neutral.
  • pHs of less than 7 indicate acidity,
  • whereas a pH of greater than 7 indicates a base.
• The pH of water is a very important measurement concerning water quality.

The Correct answer is Adding antioxidants.

Key Points

• Antioxidants are substances that slow down or prevent the oxidation process, which is the main cause of rancidity in packaged foods.
• Oxidation occurs when food reacts with oxygen in the air, leading to the deterioration of fats and oils, causing unpleasant flavors and odors.
• Adding antioxidants to food prevents the formation of peroxides, which are responsible for the rancid smell and taste.
• Commonly used antioxidants in packaged foods include butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), and ascorbic acid (Vitamin C).
• These antioxidants are particularly effective in preserving the quality of foods that contain high amounts of unsaturated fats, such as snacks, oils, and baked goods.
• Using antioxidants not only improves the shelf life of food products but also maintains their nutritional value and taste over time.
• In addition to packaged foods, antioxidants are also used in cosmetics, pharmaceuticals, and other industries to prevent oxidation.

 Additional Information

• Increasing moisture content
  • Moisture does not prevent rancidity; instead, it can encourage the growth of microorganisms, leading to the spoilage of food products.
  • Foods with high moisture content are prone to microbial contamination and require additional methods, such as refrigeration or dehydration, to preserve them.
• Keeping it in direct sunlight
  • Exposure to direct sunlight accelerates oxidation, especially in fats and oils, as ultraviolet (UV) rays promote the formation of free radicals.
  • Keeping food in sunlight can also degrade its nutritional content and alter its taste and texture.
• Storing in a warm place
  • Warm temperatures increase the rate of chemical reactions, including oxidation, leading to faster spoilage of food.
  • Foods are best stored in cool, dry places to maintain their freshness and shelf life.

The Correct answer is 78 u.

Key Points

• The formula unit mass of Calcium Fluoride (CaF2) is calculated by summing up the atomic masses of its constituent atoms.
• The atomic mass of Calcium (Ca) is given as 40 u, and the atomic mass of Fluorine (F) is 19 u.
• In the formula for Calcium Fluoride (CaF2), there is 1 atom of Calcium (Ca) and 2 atoms of Fluorine (F).
• To calculate the formula unit mass:
  • Mass contribution from Calcium = 1 × 40 u = 40 u.
  • Mass contribution from Fluorine = 2 × 19 u = 38 u.
  • Total formula unit mass = 40 u + 38 u = 78 u.
• Thus, the correct formula unit mass of Calcium Fluoride is 78 u.

 Additional Information

• Formula Unit Mass:
  • The formula unit mass refers to the sum of the atomic masses of all atoms in a chemical formula of a compound.
  • It is expressed in atomic mass units (u).
• Calcium Fluoride (CaF2):
  • Calcium Fluoride is an ionic compound consisting of Calcium (Ca²⁺) cations and Fluoride (F^-) anions.
  • It is widely used in industries, especially in optics, as it has excellent transparency to ultraviolet and infrared light.

The Correct answer is The composition varies throughout the mixture.

Key Points

• A heterogeneous mixture is one where the components are not evenly distributed, and the composition varies throughout the mixture.
• It often consists of physically distinct parts, each with different properties.
• Examples of heterogeneous mixtures include salad, sand and water, or oil and water.
• In such mixtures, the individual components can typically be separated using physical methods, such as filtration or sorting.
• The heterogeneous nature of the mixture means that its appearance is often non-uniform, and you can see the different substances visually.
• This type of mixture contrasts with a homogeneous mixture, which has a uniform composition throughout.
• Heterogeneous mixtures play a significant role in various fields, such as geology, chemistry, and material science, for studying and separating substances.

 Additional Information

• Option 1: It has a uniform composition
  • This describes a homogeneous mixture, not a heterogeneous mixture. Homogeneous mixtures have the same composition throughout, such as salt dissolved in water.
  • These mixtures appear visually uniform and are often referred to as solutions.
• Option 2: The components cannot be separated
  • This is incorrect for heterogeneous mixtures because their components can often be physically separated. For example, sand and water can be separated through filtration.
  • This description is more suitable for compounds, where components are chemically bonded and cannot be separated by physical means.
• Option 4: It contains only one phase
  • This characteristic applies to homogeneous mixtures, where only one phase (solid, liquid, or gas) is present.
  • Heterogeneous mixtures often consist of multiple phases, such as oil and water, which exist as separate liquid phases.

The Correct answer is Curdling of milk.

Key Points

• The curdling of milk is an example of a chemical change.
• A chemical change occurs when the original substance undergoes a transformation and forms a new substance with different properties.
• In the case of milk curdling, the lactic acid bacteria present in the milk convert the lactose (milk sugar) into lactic acid.
• The increase in lactic acid causes the milk proteins, specifically casein, to denature and coagulate, forming curd.
• This process is irreversible, indicating that it is a chemical change.
• The formation of curd also involves the release of a new characteristic smell and a change in texture, which are signs of a chemical reaction.
• Curdling is widely used in the preparation of various dairy products like yogurt and cheese.

 Additional Information

• Dissolution of sugar in water
  • This is a physical change as no new substances are formed during the process.
  • Sugar dissolves in water to form a homogeneous solution, and the process is reversible by evaporation of water.
• Freezing of water
  • Freezing of water is a physical change because water changes its state from liquid to solid (ice) without altering its chemical composition.
  • This process is reversible, as ice can melt back into water.
• Tearing of paper
  • Tearing of paper is a physical change because the chemical structure of the paper remains unchanged.
  • Although the shape and size of the paper may change, its chemical properties stay the same.

Key Points

• A deposition is a process by which a gas is converted into a solid.
• Sublimation is the process by which a solid is converted to gas directly without changing into liquid in between.
• Vaporisation is the process of conversion of a liquid into a gas (vapor).
• Freezing is a process of conversion of liquid into solid at the freezing point.

The correct answer is Amalgam.

Important Points

• Amalgam is a special class of alloys in which one metal is mercury.
  • Silver amalgam is the amalgam used for a dental filling.
  • Gold amalgam is the amalgam used in the extraction of gold from ore.
  • The metal mercury is kept inside an iron container because iron doesn't form an amalgam with mercury.
• Mercury is a chemical element with atomic number 80.
  • Mercury is also known as quicksilver.
  • Mercury is the metal that is liquid at room temperature.
  • Mercury is the first known superconductor.
  • Cinnabar is the ore of mercury.

Additional Information

• Brass is the alloy of copper and zinc.
• Nichrome is the alloy of nickel, chromium, and iron.
• Electrum is the alloy of gold and silver.

The correct answer is 18 g.

Key Points

Explanation:

• 0.1 mole of C₆H₁₂O₆ = Molecular mass of C6H12O6 in grams
  • 0.1 (Mass of 6C + Mass of 12H + Mass of 6O)
  • 0.1 (12 × 6 + 1 × 12 + 16 × 6)
  • 0.1 (72 + 12 + 96)
  • 18 grams

The correct answer is Potassium.

Key Points

• Potassium belongs to a group - (1) and period - (IV) of the periodic table. Hence among the given options, Potassium has a maximum atomic radius.
• Carbon and Nitrogen belong to the period - (II) of the periodic table and on the right side hence it is obvious that atomic radii of Carbon and Nitrogen are very much small than Sodium and Potassium.
• Sodium and Potassium belong to a group - (1) and  Potassium is placed below Sodium hence the atomic radius of Potassium more than Sodium.

Important Points 

• The atomic size generally decreases across a period as we move from left to right in a particular period. due to an increase in nuclear charge.
• The atomic size generally increases across groups as we move from top to bottom in a particular group due to the addition of new shells to atoms.

Additional Information

The correct answer is Ca(OH)₂.

Key Points

• When quick lime (CaO)reacts with water, lime water is produced.
• CaO +H₂O→Ca(OH)₂
• Here the product is Ca(OH)₂, which is slaked lime or lime water.
• Mainly Calcium carbonate disassociates to produce quick lime and carbon dioxide.
• Then the quick lime reacts with water and produces lime water.
• Calcium hydroxide is used in many applications, including food preparation.
• Limewater is the common name for a saturated solution of calcium hydroxide.

The correct answer is 20.

CONCEPT:

• Heavy water: It is a form of water that contains only deuterium rather than the common hydrogen-1 isotope that makes up most of the hydrogen in normal water.
  • Formula: D₂O
  • Boiling point:101.4 °C
  • Molar mass: 20 gm/mole
  • Melting point: 3.8 °C
  • Density: 1.11 gm/cm³
  • Refractive index:1.328

EXPLANATION:

• Heavy water has deuterium(D) which is an isotope of hydrogen.
• While hydrogen has 1 proton and 0 neutrons in its nucleus giving it an atomic weight of 1, deuterium has 1 proton and 1 neutron in its nucleus.
• So deuterium has atomic weight 2.
• So heavy water, which has molecular formula D₂O, has molecular mass = 16(for oxygen)+(2× 2)(for two deuteriums)= 20

The correct answer is John Dalton.

Key Points

• This law of multiple proportions is also known as Dalton's law because this law was announced (1803) by the English chemist John Dalton.
• Law of multiple proportions:
  • if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element, are in the ratio of small whole numbers.
  • Hydrogen combines with oxygen to form two compounds, water and hydrogen peroxide.
    Hydrogen + Oxygen → Water
          2g             16g          18g
    Hydrogen + Oxygen → Hydrogen Peroxide
          2g             32g          34g
  • Masses of oxygen is16 g (in water) and 32 g (in hydrogen peroxide) combine with 2g of hydrogen, bear a simple ratio, 16:32 or 1: 2.

Additional Information

• Avogadro's Law: Equal volumes of all gases at the same temperature and pressure should contain the equal number of molecules. 
• Gay Lussac's law of gaseous volume: The gases combine in a simple ratio by volume, when they are kept at constant temperature and pressure.

The correct answer is Siderite.

• Naturally occurring mineral from which a metal can be extracted is called an ore.
• The impurities present in an ore is called gangue.
• Iron ores are the minerals from which metallic iron is extracted. 
• Among the options, only siderite is an ore of Iron.
  • The chemical formula of siderite is FeCO₃.
  • Siderite consist of 48.2% of iron.
• The other important ores of iron are:
  • Magnetite.
  • Hematite
  • Goethite.
  • Limonite.
• Malachite is an ore of Copper.
• Bauxite is an ore of Aluminium.
• Anglesite is a minor ore of lead.

The correct answer is ​Bose-Einstein condensate.

Key Points

• Matters are generally categorized into 3 states:
  • Solid: Particles are held very close to each other and can't move. 
  • Liquid: Particles are close to each other but they can move around. 
  • Gas: Particles are far from each other as compared to those present in solid or liquid states and their movement is easy and fast. 
• Two more states are discovered under extreme circumstances:
  • Plasma: A superheated matter, so hot that the electrons are ripped away from the atoms forming an ionized gas. 
  • Bose-Einstein Condensate: A group of atoms cooled to absolute zero temperature(-273.15 ^oC).

Additional Information

The correct answer is Na.

• The decreasing order of atomic radius is Na (227pm) > P (195pm) > S (180pm) > Cl (175pm).

Explanation:

• When two atoms have the same value of n for the valence electrons, the atom with the greater number of protons will generally have a greater effective nuclear charge to draw the valence electrons closer to the nucleus and, thus, decrease the atomic radius. 
• Since chlorine's 17 protons are greater than sodium's 11 protons, chlorine will have a greater effective nuclear charge to draw chlorine's valence electrons closer to the nucleus and, thus, chlorine is expected to have a smaller atomic radius.
• While sodium with the lower effective nuclear charge is expected to have a larger atomic radius.

Important Points

• In the periodic table, the atomic radius of elements tends to decrease as you move across a row from left to right.
• Ionic radii increase down a group as more shells are added.

Key Points

• Sodium is highly reactive so that it is stored in oil or kerosene because it spontaneously ignites in water.
• At room temperature, sodium metal is soft enough that you can cut it with a butter knife.
• White phosphorus is used in flares and incendiary devices.
• Red phosphorus is in the material stuck on the side of matchboxes, used to strike against safety matches to light them.