List of top Chemistry Questions

How many significant figures should be present in the answer of the following calculations?

1. \(\frac {0.02856 × 298.15 × 0.112}{0.5785}\)
2. \(5 × 5.364\)
3. \(0.0125 + 0.7864 + 0.0215\)

Write the favourable factors for the formation of ionic bond.

What is the SI unit of mass? How is it defined?

A 25 watt bulb emits monochromatic yellow light of wavelength of 0.57µm. Calculate the rate of emission of quanta per second.

Use the data given in the following table to calculate the molar mass of naturally occuring argon isotopes:

Isotope	Isotopic molar mass	Abundance
36Ar	35.96755 g mol–1	0.337%
38Ar	37.96272 g mol–1	0.063%
40Ar	39.9624 g mol–1	99.600%

What do you mean by significant figures?

Pressure is determined as force per unit area of the surface. The SI unit of pressure, pascal is as shown below:
\(1\text{Pa} = 1\text{N m}^{–2} \)
If mass of air at sea level is \(1034\, \text{g cm}^{–2}\), calculate the pressure in pascal.

How do you express the bond strength in terms of bond order?

Express the following in the scientific notation: 
(i) 0.0048 
(ii) 234,000 
(iii) 8008 
(iv) 500.0 
(v) 6.0012

How many significant figures are present in the following? 
(i) 0.0025 
(ii) 208 
(iii) 5005 
(iv) 126,000 
(v) 500.0 
(vi) 2.0034

If the density of methanol is \(0.793\, \text{kg L}^{–1}\), what is its volume needed for making 2.5 L of its 0.25 M solution?

In three moles of ethane \((\text{C}_2\text{H}_6)\), calculate the following: 
(i) Number of moles of carbon atoms. 
(ii) Number of moles of hydrogen atoms. 
(iii) Number of molecules of ethane.

Round up the following upto three significant figures: 
(i) 34.216 
(ii) 10.4107 
(iii) 0.04597 
(iv) 2808

Define the bond length.

Electrons are emitted with zero velocity from a metal surface when it is exposed to radiation of wavelength 6800 Å. Calculate the threshold frequency (ν₀) and work function (W₀) of the metal.

Calculate the number of atoms in each of the following:

1. 52 moles of Ar
2. 52 u of He
3. 52 g of He.

Although both \(CO_2\) and \(H_2O\) are triatomic molecules, the shape of \(H_2O\) molecule is bent while that of \(CO_2\) is linear. Explain this on the basis of dipole moment.

A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38 g carbon dioxide, 0.690 g of water and no other products. A volume of 10.0 L (measured at STP) of this welding gas is found to weigh 11.6 g. Calculate:

1. empirical formula, 
2. molar mass of the gas, and 
3. molecular formula

Explain why \(BeH_2\) molecule has a zero dipole moment although the \(Be-H\) bonds are polar

Calcium carbonate reacts with aqueous \(HCl\) to give \(CaCl_2 \) and \(CO_2\) according to the reaction, \(CaCO_3 (s) + 2 HCl (aq) → CaCl_2 (aq) + CO_2(g) + H_2O(l)\). What mass of \(CaCO_3\) is required to react completely with \(25 \ mL\) of \(0.75 \ M\) \(HCl\)?

(i) Write the electronic configurations of the following ions: (a) H^– (b) Na⁺ (c) O₂^– (d) F^– 
(ii) What are the atomic numbers of elements whose outermost electrons are represented by (a) 3s¹ (b) 2p³ and (c) 3p⁵? 
(iii) Which atoms are indicated by the following configurations? (a) [He] 2s¹ (b) [Ne] 3s² 3p³ (c) [Ar] 4s² 3d¹.

What is the lowest value of n that allows g orbitals to exist?

Chlorine is prepared in the laboratory by treating manganese dioxide \((MnO_2)\) with aqueous hydrochloric acid according to the reaction
\(4 HCl (aq) + MnO_2(s) → 2H_2O (l) + MnCl_2(aq) + Cl_2 (g)\).
How many grams of HCl react with 5.0 g of manganese dioxide?

An electron is in one of the 3d orbitals. Give the possible values of n, l and ml for this electron.

An atom of an element contains 29 electrons and 35 neutrons. Deduce (i) the number of protons and (ii) the electronic configuration of the element.