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

The correct answer is Equal to 7.

Key Points

• A neutral salt solution has a pH of exactly 7 at standard temperature and pressure (25°C).
• This occurs because the salt is formed from a strong acid and a strong base, which completely neutralize each other.
• Examples of neutral salts include sodium chloride (NaCl) and potassium nitrate (KNO₃).
• The ions of neutral salts do not hydrolyze in water, maintaining a neutral pH in the solution.

Additional Information

• pH Scale:
  • The pH scale ranges from 0 to 14, where 7 is neutral, < 7 is acidic, and > 7 is basic.
  • The pH is calculated as the negative logarithm of hydrogen ion concentration: pH = -log[H⁺].
• Strong Acids and Bases:
  • Strong acids completely dissociate in water (e.g., HCl, HNO₃).
  • Strong bases also dissociate completely (e.g., NaOH, KOH).
• Hydrolysis of Salts:
  • Salts formed from strong acids and strong bases do not hydrolyze, resulting in a neutral solution.
  • However, salts formed from weak acids or bases may hydrolyze, affecting the pH.
• Temperature Dependence:
  • The pH of pure water and neutral solutions is exactly 7 at 25°C.
  • As temperature increases, the pH of water decreases slightly due to increased ionization, but it remains neutral.

The correct answer is Option 1.

Key Points

• The pH scale ranges from 0 to 14, where 7 is considered neutral.
• The pH of a neutral solution, such as pure water, is exactly 7.
• Values less than 7 on the pH scale represent an acidic solution.
• Values greater than 7 on the pH scale represent a basic (alkaline) solution, not an acidic one.
• The pH scale is logarithmic, meaning each whole number change represents a tenfold change in acidity/basicity.

Additional Information

• Definition of pH
  • pH stands for 'potential of Hydrogen' or 'power of Hydrogen'.
  • It measures the hydrogen ion concentration in a solution.
• Applications of pH Measurement
  • pH measurement is crucial in chemistry, biology, medicine, agriculture, and many other fields.
  • It is used to determine the acidity or alkalinity of soil, water, and other substances.
• Indicators of pH
  • Litmus paper, pH paper, and pH meters are commonly used to measure pH.
  • Indicators change color at specific pH levels, providing a visual representation of pH.
• Importance of pH in Biological Systems
  • Maintaining proper pH is essential for many biological processes.
  • Human blood has a pH of around 7.4, which is slightly basic.
  • Enzyme activity and metabolic functions are highly pH-dependent.

The correct answer is It will turn blue litmus red..

Key Points

• Ammonium chloride (NH₄Cl) is a salt that, when dissolved in water, undergoes hydrolysis to form a weak base (NH₄OH) and a strong acid (HCl).
• The solution of ammonium chloride is acidic in nature due to the presence of the strong acid (HCl).
• When an acidic solution is tested with blue litmus paper, it turns red, indicating the presence of an acid.
• This behavior confirms that the solution of ammonium chloride is acidic and will turn blue litmus paper red.

Additional Information

• Hydrolysis of Salts
  • Hydrolysis refers to the reaction of a salt with water to form an acid and a base.
  • Salts derived from strong acids and weak bases produce acidic solutions.
  • Salts derived from strong bases and weak acids produce basic solutions.
• Litmus Test
  • Litmus paper is a pH indicator used to test whether a solution is acidic or basic.
  • Blue litmus paper turns red under acidic conditions (pH < 7).
  • Red litmus paper turns blue under basic conditions (pH > 7).
• Ammonium Chloride
  • Ammonium chloride is a white crystalline salt with the formula NH₄Cl.
  • It is commonly used in fertilizers and as a flavoring agent in some types of licorice.
  • In a laboratory, it is used as a buffer solution and in the preparation of cooling baths.
• pH Scale
  • The pH scale ranges from 0 to 14 and measures the acidity or basicity of a solution.
  • A pH of 7 is considered neutral.
  • pH values less than 7 indicate acidic conditions, while values greater than 7 indicate basic conditions.

The correct answer is Did not change.

Key Points

• Sodium bicarbonate (NaHCO3) is a weak base and slightly alkaline in nature.
• pH paper is an indicator that changes color based on the pH of the substance it comes into contact with.
• Solid sodium bicarbonate typically has a pH around 8-9 when dissolved in water, but the solid form does not readily change the pH paper color.
• The color of the pH paper does not change significantly because the bicarbonate ions in the solid form are not free to react with the paper.

Additional Information

• pH Scale
  • The pH scale ranges from 0 to 14, where 7 is neutral, below 7 is acidic, and above 7 is basic (alkaline).
  • The pH paper is a tool used to measure the acidity or alkalinity of a solution.
• Sodium Bicarbonate
  • Commonly known as baking soda, sodium bicarbonate is used in cooking, cleaning, and sometimes as a medicinal antacid.
  • It is a chemical compound with the formula NaHCO3.
• Indicators
  • Indicators are substances that change color in response to changes in pH.
  • Common indicators include litmus paper, phenolphthalein, and methyl orange.
• Reactivity of Solids
  • Solid compounds are generally less reactive with indicators compared to their aqueous solutions.
  • This is because the ions in solids are not free to interact with the indicator.

The correct answer is decreases.

Key Points

• The pH value is a measure of the hydrogen ion concentration in a solution.
• As the concentration of hydronium ions (H₃O⁺) increases, the pH value decreases.
• A lower pH value indicates a higher acidity of the solution.
• The pH scale ranges from 0 to 14, with 7 being neutral, below 7 acidic, and above 7 basic.

Additional Information

• Hydronium Ion (H₃O⁺)
  • Hydronium ion is the form in which a proton (H⁺) exists in aqueous solution.
  • It is formed when an acid dissolves in water, donating a proton to a water molecule.
• pH Scale
  • The pH scale is logarithmic, meaning each whole pH value below 7 is ten times more acidic than the next higher value.
  • For example, a solution with a pH of 3 is 10 times more acidic than a solution with a pH of 4.
• Acidity and Alkalinity
  • Acidity refers to the concentration of hydrogen ions (H⁺) in a solution.
  • Alkalinity refers to the concentration of hydroxide ions (OH⁻) in a solution.
• Neutralization Reaction
  • A neutralization reaction occurs when an acid and a base react to form water and a salt.
  • This reaction generally results in the pH of the solution moving towards neutral (pH 7).

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 Sorensen.

Key Points

• The pH scale was invented by the Danish biochemist Soren Peter Lauritz Sorensen.
• He introduced this scale in 1909 to measure the acidity and basicity of substances. 

Additional Information

pH Scale:

• pH is a measure of how acidic/basic a substance is.
• pH stands for the potential of hydrogen, which refers to the concentration of hydrogen ions in a solution.
• The range goes from 0 - 14, with 7 being neutral. pHs of less than 7 indicate acidity, whereas a pH of greater than 7 indicates a base.
• pH is really a measure of the relative amount of free hydrogen and hydroxyl ions in the water. 

The correct answer is Equal to 7.

Key Points

• A neutral salt solution has a pH of exactly 7 at standard temperature and pressure (25°C).
• This occurs because the salt is formed from a strong acid and a strong base, which completely neutralize each other.
• Examples of neutral salts include sodium chloride (NaCl) and potassium nitrate (KNO₃).
• The ions of neutral salts do not hydrolyze in water, maintaining a neutral pH in the solution.

Additional Information

• pH Scale:
  • The pH scale ranges from 0 to 14, where 7 is neutral, < 7 is acidic, and > 7 is basic.
  • The pH is calculated as the negative logarithm of hydrogen ion concentration: pH = -log[H⁺].
• Strong Acids and Bases:
  • Strong acids completely dissociate in water (e.g., HCl, HNO₃).
  • Strong bases also dissociate completely (e.g., NaOH, KOH).
• Hydrolysis of Salts:
  • Salts formed from strong acids and strong bases do not hydrolyze, resulting in a neutral solution.
  • However, salts formed from weak acids or bases may hydrolyze, affecting the pH.
• Temperature Dependence:
  • The pH of pure water and neutral solutions is exactly 7 at 25°C.
  • As temperature increases, the pH of water decreases slightly due to increased ionization, but it remains neutral.

The correct answer is Option 1.

Key Points

• The pH scale ranges from 0 to 14, where 7 is considered neutral.
• The pH of a neutral solution, such as pure water, is exactly 7.
• Values less than 7 on the pH scale represent an acidic solution.
• Values greater than 7 on the pH scale represent a basic (alkaline) solution, not an acidic one.
• The pH scale is logarithmic, meaning each whole number change represents a tenfold change in acidity/basicity.

Additional Information

• Definition of pH
  • pH stands for 'potential of Hydrogen' or 'power of Hydrogen'.
  • It measures the hydrogen ion concentration in a solution.
• Applications of pH Measurement
  • pH measurement is crucial in chemistry, biology, medicine, agriculture, and many other fields.
  • It is used to determine the acidity or alkalinity of soil, water, and other substances.
• Indicators of pH
  • Litmus paper, pH paper, and pH meters are commonly used to measure pH.
  • Indicators change color at specific pH levels, providing a visual representation of pH.
• Importance of pH in Biological Systems
  • Maintaining proper pH is essential for many biological processes.
  • Human blood has a pH of around 7.4, which is slightly basic.
  • Enzyme activity and metabolic functions are highly pH-dependent.

The correct answer is It will turn blue litmus red..

Key Points

• Ammonium chloride (NH₄Cl) is a salt that, when dissolved in water, undergoes hydrolysis to form a weak base (NH₄OH) and a strong acid (HCl).
• The solution of ammonium chloride is acidic in nature due to the presence of the strong acid (HCl).
• When an acidic solution is tested with blue litmus paper, it turns red, indicating the presence of an acid.
• This behavior confirms that the solution of ammonium chloride is acidic and will turn blue litmus paper red.

Additional Information

• Hydrolysis of Salts
  • Hydrolysis refers to the reaction of a salt with water to form an acid and a base.
  • Salts derived from strong acids and weak bases produce acidic solutions.
  • Salts derived from strong bases and weak acids produce basic solutions.
• Litmus Test
  • Litmus paper is a pH indicator used to test whether a solution is acidic or basic.
  • Blue litmus paper turns red under acidic conditions (pH < 7).
  • Red litmus paper turns blue under basic conditions (pH > 7).
• Ammonium Chloride
  • Ammonium chloride is a white crystalline salt with the formula NH₄Cl.
  • It is commonly used in fertilizers and as a flavoring agent in some types of licorice.
  • In a laboratory, it is used as a buffer solution and in the preparation of cooling baths.
• pH Scale
  • The pH scale ranges from 0 to 14 and measures the acidity or basicity of a solution.
  • A pH of 7 is considered neutral.
  • pH values less than 7 indicate acidic conditions, while values greater than 7 indicate basic conditions.

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.