Acids, Bases and Salts MCQ Quiz - Objective Question with Answer for Acids, Bases and Salts - Download Free PDF

CONCEPT:

Acid Rain and pH

• Acid rain refers to rainwater that has been made acidic due to the absorption of sulfur dioxide (SO₂) and nitrogen oxides (NO_x) from the atmosphere.
• The pH scale ranges from 0 to 14, where a pH of 7.0 is neutral, values below 7.0 are acidic, and values above 7.0 are basic.
• Natural, unpolluted rainwater has a slightly acidic pH of around 5.6 due to the presence of dissolved carbon dioxide (CO₂) forming carbonic acid (H₂CO₃).
• For rainwater to be classified as acid rain, its pH must be less than 5.6, which indicates the presence of stronger acids such as sulfuric acid (H₂SO₄) and nitric acid (HNO₃).

EXPLANATION:

• A pH of 7.0 indicates neutral water, which is not acidic.
• A pH of 6.6 is slightly acidic but does not qualify as acid rain since it is higher than the threshold of 5.6.
• A pH of 5.6 is the natural pH of unpolluted rainwater and marks the upper limit for acid rain.
• A pH of 8.0 is basic, which is opposite to acidic conditions.
• To classify rainwater as acid rain, its pH must be less than 5.6.

Therefore, the correct answer is 5.6.

CONCEPT:

pH Scale and Hydrogen Ion Concentration

• The pH scale is used to measure the hydrogen ion concentration in a solution.
• The scale typically ranges from 0 to 14, where:
  • pH < 7 indicates an acidic solution.
  • pH = 7 indicates a neutral solution.
  • pH > 7 indicates a basic solution.
• The term "p" in pH stands for "potenz," which means "power" in German.

EXPLANATION:

•  "A scale measuring hydrogen ion concentration in a solution is called pH scale" - This statement is correct as the pH scale measures the hydrogen ion concentration.
• "The higher the hydrogen ion concentration in a solution, higher is its pH" - This statement is NOT correct. In fact, higher hydrogen ion concentration corresponds to a LOWER pH (more acidic), not higher pH.
•  "We can measure pH generally from 0 to 14 on a pH scale" - This statement is correct as the pH scale typically ranges from 0 to 14.
• "The 'p' in pH stands for 'potenz' in German meaning power" - This statement is correct as "p" in pH indeed stands for "potenz."
• Thus, the statement in Option 2 is incorrect.

Therefore, the correct answer is The higher the hydrogen ion concentration in a solution, higher is its pH.

The correct answer is The pH will decrease.

Key Points

• The solution with pH 8 is slightly basic. Diluting it with an equal volume of water reduces the concentration of hydroxide ions (OH⁻).
• As the concentration of OH⁻ ions decreases, the solution becomes less basic, causing the pH to decrease.
• pH is logarithmic, meaning small changes in ion concentration can lead to noticeable shifts in pH.
• When diluting any solution, the pH change depends on the original pH and the extent of dilution, but water dilution generally moves the pH closer to neutral (7).
• The pH decrease will not be drastic, as the solution is already near neutral, but it will be slightly lower than 8.

Additional Information

• pH Scale:
  • pH measures the acidity or basicity of a solution on a scale of 0-14.
  • Values below 7 indicate acidity, 7 is neutral, and values above 7 indicate basicity.
• Logarithmic Nature of pH:
  • The pH scale is logarithmic, meaning each unit represents a tenfold change in hydrogen ion concentration.
  • A solution with pH 8 has 10 times fewer hydrogen ions than a solution with pH 7.
• Effect of Dilution on pH:
  • Adding water dilutes the concentration of ions present in the solution.
  • For basic solutions, dilution decreases the concentration of OH⁻ ions, lowering the pH.
• Neutral Point:
  • Pure water at 25°C has a pH of 7, considered neutral.
  • When solutions are diluted, their pH tends to move closer to the neutral point.

The Correct answer is The sting injects methanoic acid.

Key Points

• Bee stings are painful because they inject methanoic acid (also known as formic acid) into the skin.
• This acid causes a burning sensation and can lead to redness, swelling, and inflammation at the site of the sting.
• The injection of methanoic acid triggers the body's immune response, which includes the release of histamines leading to pain and irritation.
• Methanoic acid is a weak acid, but in the concentrated form as injected by bees, it can cause significant discomfort.
• The severity of the reaction can vary based on individual allergies and the number of stings received.

 Additional Information

• The sting releases carbon dioxide gas
  • This is incorrect because a bee sting does not release carbon dioxide gas; instead, it injects a liquid containing methanoic acid.
• The sting injects a mild sugar solution
  • Bee stings do not involve the injection of a sugar solution; they inject methanoic acid which causes pain and inflammation.
• The sting contains a strong base
  • A bee sting does not contain a strong base; it contains methanoic acid, which is an acid, not a base.

The Correct answer is Equal to 7.

Key Points

• A neutral salt solution is formed when a strong acid reacts with a strong base.
• The resulting solution has a pH of 7, which is considered neutral.
• pH is a scale used to specify the acidity or basicity of an aqueous solution.
• A pH of 7 indicates a neutral solution, meaning it is neither acidic nor basic.
• Examples of neutral salts include sodium chloride (NaCl) and potassium nitrate (KNO₃).

 Additional Information

• Less than 7
  • A pH less than 7 indicates an acidic solution.
  • This occurs when a strong acid reacts with a weak base, producing an acidic salt solution.
• Depends on the temperature
  • While temperature can slightly affect the pH, a neutral salt solution typically remains close to pH 7.
  • Extreme temperatures can alter the dissociation of water, but under normal conditions, the effect is minimal.
• More than 7
  • A pH more than 7 indicates a basic (alkaline) solution.
  • This occurs when a strong base reacts with a weak acid, producing a basic salt solution.

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 Sodium hydroxide.

Key Points 

• Sodium hydroxide (NaOH) dissociates completely in water to give Na+ and OH−
• Sodium hydroxide is considered a strong base as all the available [OH] in NaOH is present in the solution as [OH−] and available to accept protons.
• Sodium hydroxide is the strongest base because it totally dissociates to form sodium ions and hydroxide ions.
• These hydroxide ions are treated with hydrogen ions further from the acid and totally ionize the hydrogen ions.
• Producers may utilize sodium hydroxide to manufacture soaps, rayon, paper, products that explode, dyes, and petroleum products.
• Other works that may utilize sodium hydroxide comprise preparing cotton fabric, metal cleaning and preparing, oxide coating, electroplating, and electrolytic extraction.
• It has the pH value of about 14.​

Additional Information

• ​The blood has a normal pH range of 7.35 to 7.45.
• Milk of Magnesia is basic in nature. The pH value of the Milk of Magnesia is 10.5.
• Lemon juice has a pH between 2 and 3.

The correct answer is 10.

Key Points

• Milk of Magnesia is the magnesium compound which acts as an antacid.
• The term milk of magnesia was first used by English pharmacist Charles Henry Phillips in 1872.
• Milk of Magnesia is basic in nature.
• The pH value of the Milk of Magnesia is 10.

Additional Information

• The scale used to express the acidic or alkaline nature of a substance based on the concentration of hydrogen ions in its solution is called a pH scale.
• pH scale was discovered by Soren Sorensen.
  • The pH value of the acids are less than 7 (0 to 7)
• Acid substances usually produce a sour taste.
  • The pH value of the Bases are greater than 7 (7 to 14)
• Base substances usually produce a bitter taste.
• The pH value of the neutral substance is equal to 7.
• The pH value of the pure water is 7.
• The pH value of the blood is close to 7.4.

The correct answer is Red.

Key Points

•  Acid
  • ​Acid changes the colour of blue litmus to Red.
  • A Brnsted-Lowry acid or Lewis acid is a molecule or ion that can either donate a proton (the hydrogen ion, H+) or establish a covalent bond with an electron pair. Proton donors, also known as Brnsted-Lowry acids, are the first class of acids.
  • Proton donors, also referred to as Arrhenius acids, generate the hydronium ion H3O+ under the unique situation of aqueous solutions.
  • The Arrhenius theory was expanded upon by Brnsted and Lowry to take non-aqueous solvents into account.
  • A hydrogen atom is typically bound to a chemical structure in a Brnsted or Arrhenius acid that is still energetically advantageous after the loss of H+.

Additional Information

• Aqueous Arrhenius acids have distinguishing characteristics that serve as a useful definition of an acid. Acids can turn blue litmus red, produce aqueous solutions with a sour taste, and react with bases and some metals (like calcium) to generate salts.
• The Latin word acidus, which means "sour," is where the word acid comes from. While the technical definition solely refers to the solute, an aqueous solution of an acid with a pH lower than 7 is sometimes commonly referred to as "acid" (as in "dissolved in acid"..
• Higher acidity and, thus, a higher concentration of positive hydrogen ions in the solution are indicative of a lower pH. 

The correct answer is Both I and II.

Key Points

• Indicators are the substances that are used to identify whether the given substance is an acid or a base.
• There are two types of indicators:
  • Natural: These indicators are obtained from natural sources like plants. 
  • Turmeric, litmus, china rose petals, etc., are some of the naturally occurring indicators. Hence, option 4 is correct.
  • The most commonly used natural indicator is litmus.
  • It is extracted from lichens.
  • It is available in the form of a solution, or in the form of strips of paper, known as litmus paper.
  • Generally, it is available as red and blue litmus paper.
  • Man-made: Phenolphthalein, Methyl orange are some of the man-made indicators.

Important Points

• The indicators change their color when added to a solution containing an acidic or a basic substance.
• Turmeric is a natural indicator. It contains the substance curcumin which changes color with pH.
• When a substance is basic, the color is red, whereas when the substance is acidic, the color of turmeric turns yellow to brown.
• Films containing aqueous hibiscus extract were developed as a natural pH indicator.
• Natural polymers (chitosan, gelatine, and starch) were used for the film production.
• Great color changes from pink (pH = 2.0) to yellow (pH = 13.0) were observed.
• Acids turn blue litmus red. Bases do not change the color of blue litmus.
• Acids do not change the color of red litmus. Bases turn red litmus blue.

Additional Information 

Some indicators and their color change are given in the table below:

The correct answer is 7.

Key Points

•  A solution's acidity can be determined by looking at its pH, which is a measurement of hydrogen ion concentration. Pure water slightly separates into ions with roughly equal amounts of hydrogen and hydroxyl (OH) ions. [H+] is 107 for a neutral solution, or pH = 7.
• By chance, the amounts of H+ and OH- are equal at pH 7. Because of this, pH 7 is regarded as the neutral pH. The concentration of H+ exceeds the concentration of OH- below pH 7, causing the water to become acidic.
• Because pure water has a pH of exactly 7, a pH value of 7 is considered neutral. Levels under 7 are considered acidic, whereas those over 7 are considered basic or alkaline.​

Additional Information

• pH stands for "Potential of Hydrogen" in its full form.
• The negative logarithm of the concentration of H+ ions is known as pH.
• As a result, the meaning of pH is defined as the strength or power of hydrogen.
• For human life to exist, the serum's pH must be carefully regulated at around 7.4 (a slightly alkaline range of 7.35 to 7.45).

The correct answer is It decreased.

Key Points

• The pH scale measures how acidic or alkaline a substance is.
• A pH scale has a range of 0 to 14. An acidic solution has a pH less than 7 while an alkaline solution has a pH more than 7. The solution with pH 7 is neutral, that is, its neither acidic or basic.
• When the temperature is increased, the degree of decomposition in acidic solution increases, this eventually lowers or decreases the pH of the solution
• Thus, when Babu took some quantity of dilute nitric acid in a test tube and heated the test tube at 70°C for about 10 minutes, the pH of nitric acid decreases with increase in temperature.

The correct answer is Halite.

Key Points

• Halite is the mineral form of sodium chloride (NaCl), commonly known as rock salt.
• Halite forms through the evaporation of seawater and is typically found in sedimentary rock formations.
• It is an evaporite mineral, which means it crystallizes from evaporating brine.
• Commercially, halite is mined for use as table salt, road salt, and in various industrial processes.
• Halite crystals are typically cubic in structure and can range in color from clear to white, and sometimes even shades of pink or blue due to impurities.

 Additional Information

• Hematite
  • Hematite is an iron oxide mineral with the formula Fe₂O₃.
  • It is one of the most abundant minerals on Earth's surface and in the shallow crust.
  • Hematite is primarily used in the production of iron and steel.
  • The mineral can appear in colors such as black to steel or silver-gray, brown to reddish-brown, or red.
• Limonite
  • Limonite is a generic term for a mixture of hydrated iron oxide minerals.
  • It is often used as a low-grade iron ore and can be found in various geological environments.
  • Limonite is typically yellow-brown or ochre-colored.
• Siderite
  • Siderite is a carbonate mineral composed of iron(II) carbonate (FeCO₃).
  • It is a valuable iron mineral, used in the production of iron and steel.
  • Siderite is typically found in sedimentary deposits and can vary in color from yellow to brownish or gray.

The correct answer is 0-7

Explanation:

• The pH scale is a measure of the acidity or basicity of an aqueous solution.
• The scale ranges from 0 to 14, where
  • 7 is neutral,
  • Values less than 7 indicate acidity
  • Values greater than 7 indicate a basic solution.
• Acids are substances that can donate a proton (H+) and have a pH value less than 7.
• The standard pH range for acids is from 0 to 7. This is because acids are characterized by their ability to increase the concentration of hydrogen ions (H+) in a solution, resulting in a lower pH.