Mole Concept — Set 3
Chemistry · मोल संकल्पना · Questions 21–30 of 40
The charge carried by 1 mole of electrons is approximately?
Correct Answer: D. 9.65 × 10^4 C
Option D is correct because 1 mole of electrons carries about 9.65 × 10^4 C of charge. This value is called Faraday’s constant. It equals NA multiplied by the charge of one electron.
Gram molecular mass of a substance means?
Correct Answer: C. Mass of 1 mole expressed in grams
Option C is correct because gram molecular mass is the mass of one mole in grams. Its numerical value equals the molecular mass. For example, 1 mole of H2O has mass 18 g.
At STP, the volume occupied by 0.50 mol of an ideal gas is?
Correct Answer: C. 11.2 L
Option C is correct because volume at STP = moles × 22.4 L = 0.50 × 22.4 = 11.2 L. Molar volume at STP is used for ideal gas conversions. Doubling moles doubles the volume at the same conditions.
Why does molarity generally change with temperature?
Correct Answer: C. Because solution volume can change with temperature
Option C is correct because molarity depends on volume of solution, which can expand or contract with temperature. The moles of solute usually remain the same in a closed container. Therefore, concentration in mol/L can vary with temperature.
Why is molality generally considered temperature independent?
Correct Answer: A. Because it uses mass of solvent, not volume
Option A is correct because molality is based on mass of solvent, which does not change with temperature. It is defined as moles of solute per kilogram of solvent. Therefore, molality stays the same even if volume changes.
For any mixture, the sum of mole fractions of all components is?
Correct Answer: D. Equal to 1
The correct answer is 'Equal to 1'. Option D is correct because mole fractions are defined as parts of the total moles. Adding all parts must give the whole, which is 1. Mole fraction is unitless and ranges from 0 to 1.
How much NaOH is needed to prepare 500 mL of 0.20 M NaOH solution? (NaOH = 40 g/mol)?
Correct Answer: C. 4.0 g
Option C is correct because moles needed = M × V(L) = 0.20 × 0.500 = 0.10 mol. Mass = moles × molar mass = 0.10 × 40 = 4.0 g. This uses molarity to find moles and then converts to grams.
How many formula units are present in 2.5 g of CaCO3? (CaCO3 = 100 g/mol)?
Correct Answer: A. 1.5055 × 10^22
Option A is correct because moles = 2.5/100 = 0.025 mol. Formula units = 0.025 × 6.022 × 10^23 = 1.5055 × 10^22. Each formula unit represents one CaCO3 unit in an ionic solid.
A compound contains 40.0% C, 6.67% H, and 53.33% O by mass. Its empirical formula is?
Correct Answer: C. CH2O
Option C is correct because moles in 100 g are C:40/12=3.33, H:6.67/1=6.67, O:53.33/16=3.33. Dividing by 3.33 gives the ratio 1:2:1, so CH2O. Empirical formula shows the simplest whole-number ratio of atoms.
If the empirical formula is CH2O and the molar mass is 180 g/mol, the molecular formula is?
Correct Answer: A. C6H12O6
Option A is correct because empirical mass of CH2O is 12+2+16 = 30 g/mol. The multiplier n = 180/30 = 6, so molecular formula = (CH2O)6. This gives C6H12O6.