The equivalent weight of oxalic acid in C₂H₂O₄·2H₂O is
- A.45
- B.63
- C.90
- D.126
Correct answer
Explanation
The correct answer is B, 63. Hydrated oxalic acid has a molar mass of 126 and is a dibasic acid, so its equivalent weight is 126 ÷ 2 = 63.
The molar mass of C₂H₂O₄·2H₂O is (2 × 12) + (2 × 1) + (4 × 16) + 2 × 18 = 24 + 2 + 64 + 36 = 126 g/mol. Oxalic acid, (COOH)₂, has two replaceable hydrogen atoms, so its basicity is 2. The equivalent weight of an acid is its molar mass divided by its basicity. Crystalline oxalic acid is a common primary standard in titrations against potassium permanganate and sodium hydroxide.
A is wrong because 45 is the equivalent weight of anhydrous oxalic acid (90 ÷ 2), without the two water molecules.
C is wrong because 90 is the molar mass of anhydrous oxalic acid, not an equivalent weight.
D is wrong because 126 is the molar mass of the hydrated acid; it has not been divided by the basicity.
Exam tip: equivalent weight of an acid = molar mass ÷ basicity; hydrated oxalic acid: 126 ÷ 2 = 63.
Practice Questions
View allThe potential difference between the terminals of an electrical heating device is 40 V, when it draws a current of 2 A from the source. Which one of the following is the correct value of current drawn by the heating device if the potential is increased to 140 V?
- A.7 A
- B.5 A
- C.4 A
- D.2 A
Show answer
By Ohm's law the heater's resistance is 40 V divided by 2 A, which is 20 ohms, so at 140 V it draws 140 divided by 20, or 7 A. Ohm's law states that, at constant temperature, the current through a conductor is directly proportional to the potential difference across…
Read the full explanation →Consider the following statements in the light of octane number and cetane number of fuels: 1. Cetane number is used for gasoline and octane number is used for diesel. 2. Octane number of n-hexadecane is 100 and cetane number of isooctane is 100. Which of the statements given above is/are correct?
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
Show answer
Both statements swap the two scales: octane number rates petrol, cetane number rates diesel, and their reference fuels are the other way round.
Read the full explanation →Which one among the following statements related to human eye is correct?
- A.For a person suffering from short-sight defect, the image of a distant object is focused behind the retina.
- B.Short-sight defect can be corrected by a converging spectacle lens.
- C.For a person suffering from long-sight defect, the image of a near object is focused behind the retina.
- D.Long-sight defect can be corrected by a diverging spectacle lens.
Show answer
In long-sightedness (hypermetropia) the eye cannot see nearby objects clearly because their image is formed behind the retina.
Read the full explanation →When sunlight (white light) falls on a triangular glass prism, a band of colours called a spectrum is obtained. Which one among the following represents this effect appropriately?
- A.Reflection
- B.Diffraction
- C.Refraction
- D.Dispersion
Show answer
The splitting of white light into its seven component colours by a prism is called dispersion. White light is a mixture of colours, and glass bends each colour by a different amount because its refractive index depends on wavelength.
Read the full explanation →Which one of the following statements is correct?
- A.The number of electrons in alpha particle is 2.
- B.The coordination number of EDTA is 6.
- C.The charge of beta (β) particle is +2.
- D.Both carbon and silicon form ionic compounds.
Show answer
EDTA is a hexadentate ligand: one EDTA ion binds a metal ion through six donor atoms, so it forms complexes with coordination number 6.
Read the full explanation →