Acid, Base and Salt Archives

71. Which one of the following gases dissolves in water to give acidic

Which one of the following gases dissolves in water to give acidic solution?

[amp_mcq option1=”Carbon dioxide” option2=”Oxygen” option3=”Nitrogen” option4=”Hydrogen” correct=”option1″]

This question was previously asked in

UPSC CDS-1 – 2018

Carbon dioxide (CO₂) dissolves in water to form carbonic acid (H₂CO₃). Carbonic acid is a weak acid that partially dissociates into hydrogen ions (H⁺) and bicarbonate ions (HCO₃⁻), thus lowering the pH and making the solution acidic. The reaction is CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻.

– An acidic solution is formed when a substance dissolves in water and increases the concentration of hydrogen ions (H⁺) or hydronium ions (H₃O⁺).
– Non-metal oxides, like carbon dioxide, often react with water to form acids.
– Oxygen, Nitrogen, and Hydrogen are non-polar or weakly polar molecules that dissolve in water but do not react chemically to produce acidic or basic solutions; they remain neutral.

The acidity of solutions of gases like CO₂ is important in various natural processes, such as the formation of acid rain (from oxides of sulfur and nitrogen) and the buffering system in blood involving carbonic acid and bicarbonate. The dissolution of CO₂ in oceans leads to ocean acidification.

72. The molecular mass of sulphuric acid is 98. If 49 g of the acid is dis

The molecular mass of sulphuric acid is 98. If 49 g of the acid is dissolved in water to make one litre of solution, what will be the strength of the acid?

[amp_mcq option1=”Two normal” option2=”One normal” option3=”0·5 normal” option4=”Four normal” correct=”option2″]

This question was previously asked in

UPSC CDS-1 – 2017

Download PDF Attempt Online

The molecular mass of sulfuric acid (H₂SO₄) is 98 g/mol. 49 g of H₂SO₄ is dissolved in water to make 1 litre of solution.
Number of moles of H₂SO₄ = Mass / Molar mass = 49 g / 98 g/mol = 0.5 mol.
The molarity of the solution is Moles / Volume (L) = 0.5 mol / 1 L = 0.5 M.
Normality (N) is defined as Molarity (M) multiplied by the n-factor (equivalents per mole). For sulfuric acid acting as an acid, it has two acidic protons (H⁺) that can be donated, so its n-factor is 2.
Normality = Molarity × n-factor = 0.5 M × 2 = 1 N.
The strength of the acid solution is one normal.

Normality is a measure of concentration defined as the number of gram equivalents of solute per litre of solution. For acids, the gram equivalent weight is the molecular weight divided by the number of acidic protons per molecule.

Sulfuric acid is a strong diprotic acid, meaning it can donate two protons in acid-base reactions. Its equivalent weight for neutralization reactions is Molecular Weight / 2 = 98 / 2 = 49 g/equivalent. Therefore, 49 g of H₂SO₄ in 1 litre is 1 Normal.

73. The pH value of a sample of multiple-distilled water is

The pH value of a sample of multiple-distilled water is

[amp_mcq option1=”zero” option2=”14″ option3=”very near to zero” option4=”very near to seven” correct=”option4″]

This question was previously asked in

UPSC CDS-1 – 2017

Download PDF Attempt Online

The correct answer is D) very near to seven.

pH is a measure of the acidity or alkalinity of a solution. Pure water is neutral because the concentration of hydrogen ions (H⁺) equals the concentration of hydroxide ions (OH⁻) produced by the auto-ionization of water (H₂O ⇌ H⁺ + OH⁻). At standard temperature (25°C), in pure water, [H⁺] = 10⁻⁷ mol/L. The pH is defined as -log₁₀[H⁺]. Thus, the pH of pure water is -log₁₀(10⁻⁷) = 7. Multiple-distilled water is highly purified water with most impurities removed. While it’s difficult to achieve a perfect pH of 7 in practice (e.g., due to dissolved CO₂ from the air forming carbonic acid, making it slightly acidic, or dissolved substances from the container), the theoretical and practical pH of pure, neutral water is very close to 7.

A pH of zero indicates a highly acidic solution (e.g., 1M HCl). A pH of 14 indicates a highly alkaline solution (e.g., 1M NaOH). Values very near zero would indicate strong acidity, which is not characteristic of pure water. Values very near seven indicate neutrality, which is the property of pure water.