Abhyaas 1.0

Which of the following sets of quantum numbers is not possible?

• n-2,l-1, m_l= 0, m_s=-1/2

• n-3,l-2, m_l =-2, m_s =+1/2

• n-1,l-0, m_l= -0, ms=+1/2

• n-3,1=3, m_l = +2, m_s=-1/2

Answer explanation

The set n-3, l=3, ml=+2, ms=-1/2 is not possible because the value of ml cannot exceed the value of l.

Which of the following is the correct definition of a mole?

• The mass of one molecule of a substance in grams.

• The number of molecules in one gram of a substance.

• The amount of substance that contains as many entities (atoms, molecules, ions, etc) as there are in 12 grams of carbon-12.

• The volume of one mole of a substance at standard temperature and pressure.

Answer explanation

The correct definition of a mole is the amount of substance that contains as many entities (atoms, molecules, ions, etc) as there are in 12 grams of carbon-12.

Assertion: Avogadro's law states that equal volumes of all gases at the same temperature and pressure contain equal numbers of molecules. Reason: The volume occupied by gas molecules is negligible compared to the total volume of the gas.

• Both (A) and (R) are true and (R) is the correct explanation of (A).

• Both (A) and (R) are true but (R) is not the correct explanation of (A).

• (A) is true but (R) is false.

• (A) is false but (R) is true.

Answer explanation

Both (A) and (R) are true but (R) is not the correct explanation of (A).

Assertion: Electronegativity increases across a period in the periodic table. Reason: Effective nuclear charge increases across a period.

• Both (A) and (R) are true and (R) is the correct explanation of (A).

• Both (A) and (R) are true but (R) is not the correct explanation of (A).

• (A) is true but (R) is false.

• (A) is false but (R) is true.

Answer explanation

Both (A) and (R) are true and (R) is the correct explanation of (A).

Explain the following: a) Oxygen has lower ionization enthalpy than nitrogen. b) The electron gain enthalpy of fluorine is less negative than that of chlorine.

Answer explanation

a) Oxygen has lower ionization enthalpy than nitrogen due to increased shielding effect. b) Fluorine has less negative electron gain enthalpy than chlorine due to smaller size and higher electron-electron repulsions.

Aluminum reacts with chlorine gas to form aluminum chloride via the following reaction: 2Al + 3Cl2 --> 2AlCl3 (Molar mass of Al: 27g, Cl: 35.5g) a) Which is the limiting reagent? How many grams of aluminum chloride could be produced from 34.0 g of aluminum and 39.0 g of chlorine gas?

Answer explanation

The limiting reagent is aluminum. To find the grams of AlCl3 produced, calculate moles of Al and Cl2, determine limiting reagent, then use stoichiometry to find grams of AlCl3.

Empirical formula represents the simplest whole number ratio of various atoms present in a compound. a) Give the relation between empirical formula and molecular formula. b) An organic compound has the following percentage composition C= 12.36%, H = 2.13%, Br = 85%. Its vapour density is 94. Find its molecular formula.

Answer explanation

a) The empirical formula is the simplest whole number ratio of atoms, while the molecular formula shows the actual number of each atom in a compound. b) The molecular formula of the compound is C2H4Br2.

Write the n and l values of a 4d electron.

Answer explanation

The n value for a 4d electron is 4, and the l value can range from 0 to 3. Therefore, the n value is 4 and the l value can be 0, 1, 2, or 3.

Give the names of series of spectral lines of atomic hydrogen and their region in the electromagnetic spectrum. Write electronic configuration for Cu (At No:29) and Cr(At No 24).

Answer explanation

The series of spectral lines of atomic hydrogen are Lyman, Balmer, Paschen, Brackett, Pfund. Their regions in the electromagnetic spectrum are ultraviolet, visible, infrared, infrared, and infrared respectively. Electronic configuration for Cu (At No:29) is [Ar] 3d10 4s1 and for Cr (At No 24) is [Ar] 3d5 4s1.

State the dual behaviour of matter. A moving electron has a de Broglie wavelength of 7 x 10^-7 m. Calculate its kinetic energy. (Planck's constant = 6.626 x 10^-34 Js, mass of an electron = 9.1 x 10^-31 kg)

Answer explanation

The dual behavior of matter refers to its wave-particle duality. The de Broglie wavelength of a moving electron can be used to calculate its kinetic energy using the formula: KE = (h^2) / (2 * m * lambda^2), where h is Planck's constant, m is the mass of the electron, and lambda is the de Broglie wavelength. Substituting the given values into the formula will give the kinetic energy.