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ChemistryClass 11CBSE

2.8×10⁻³ mol of CO₂ is left after removing 10²¹ molecules from its ‘x’ mg sample. Find x. (Nₐ = 6.02×10²³ mol⁻¹)

Molar mass of CO₂ = 44 g/molStep 1 — Convert removed molecules to moles:Moles removed = 10²¹ / (6.02×10²³) = 1.661×10⁻³ molStep 2 — Initial moles = remaining + removed:n_initial = 2.8×10⁻³ + 1.661×10⁻³ = 4.461×10⁻³ molStep 3 — Initial mass:mass = 4.461×10⁻³ × 44 = 0.19629 g = 196.3 mgAnswer: x ≈ 196.3 mgDividing molecule count by Nₐ gives moles; multiplying by molar mass gives mass the two-step core of all JEE mole-concept problems.

ChemistryClass 11CBSE

Total number of isomers, considering both structural and stereoisomers of cyclic ethers with the molecular formula C₄H₈O is

Degree of unsaturation = (2×4 + 2 − 8) / 2 = 1 → One ring, no double bonds.A cyclic ether contains one O atom inside the ring. Possible ring sizes: 3-membered (oxirane), 4-membered (oxetane), 5-membered (tetrahydrofuran).StructureIsomer Count2,2-dimethyloxirane1(R)-ethyloxirane1(S)-ethyloxirane1cis-2,3-dimethyloxirane (meso)1(R,R)-2,3-dimethyloxirane1(S,S)-2,3-dimethyloxirane13-methyloxetane1Tetrahydrofuran (THF)1Answer: 8 isomersAlways check for stereocentres in epoxide rings. The meso compound of 2, 3-dimethyloxirane is a frequent JEE trap.

ChemistryClass 11CBSE

What does 1s, 2s, 2p, 3s, 3p mean?

NotationShellSubshellMax Electrons1s1sts (spherical)22s2nds22p2ndp (dumbbell)63s3rds23p3rdp6Number = energy level (shell) | Letter = subshell type.

ChemistryClass 11CBSE

Why is it incorrect to say that an electron is 'stationary' in an atom?

It is incorrect because electrons are constantly in motion, orbiting or existing in a probability cloud around the nucleus. Their movement is a fundamental aspect of atomic structure and behavior.Electrons are not static. Their continuous motion is responsible for phenomena like chemical bonding and the atom's magnetic properties. Quantum mechanics describes their location as a probability distribution rather than a fixed orbit, but it always implies motion.

ChemistryClass 11CBSE

Imagine you have an unknown element. What single piece of information about its subatomic particles would immediately allow you to identify the element?

The number of protons (or its atomic number) would immediately allow you to identify the element.As stated, the atomic number (number of protons) is unique to each element. Knowing this value is sufficient to identify the element on the periodic table.

ChemistryClass 11CBSE

How does the concept of 'electron shells' or 'energy levels' further refine our understanding of electron 'orbiting'?

Electron shells or energy levels suggest that electrons don't orbit randomly, but occupy specific regions at discrete energy states around the nucleus. This explains the quantized nature of electron energies and how they absorb and emit light.The Bohr model and later quantum mechanical models introduced the idea that electrons exist in specific energy levels or shells. This isn't a simple planetary orbit but a probabilistic distribution of electrons within these defined energy regions, explaining atomic stability and spectral lines.

ChemistryClass 11CBSE

What is the primary force that holds the protons and neutrons together within the nucleus, despite the electrostatic repulsion between protons?

The primary force is the strong nuclear force (or strong interaction).Protons, being positively charged, naturally repel each other. The strong nuclear force is an extremely powerful attractive force that acts over very short distances, overcoming this electrostatic repulsion to bind the nucleons (protons and neutrons) together in the nucleus.

ChemistryClass 11CBSE

Explain why the mass number is always a whole number, even though atomic masses often have decimal values.

The mass number represents the count of whole protons and neutrons in a single atom's nucleus, which are discrete particles. Atomic masses, however, are weighted averages of the masses of all naturally occurring isotopes of an element, which often results in decimal values.

ChemistryClass 11CBSE

If an atom has an atomic number of 20 and is electrically neutral, how many protons, neutrons, and electrons could it potentially have (give one possible combination)?

Protons = 20, Electrons = 20. For neutrons, it could vary, for example, 20 neutrons, making the mass number 40.Atomic number 20 means 20 protons. For neutrality, it must have 20 electrons. The number of neutrons can vary, creating isotopes. A common isotope for an element with 20 protons (Calcium) often has 20 neutrons.

ChemistryClass 11CBSE

How does the concept of 'orbiting' electrons relate to the overall size and volume of an atom?

The 'orbiting' electrons occupy a vast region of space around the nucleus, defining the overall size and volume of the atom. The nucleus itself is extremely small in comparison.Despite the nucleus containing almost all the mass, the electrons, due to their rapid motion and the probabilistic nature of their location, determine the atomic radius and, consequently, the atom's volume. The atom is mostly empty space.

ChemistryClass 11CBSE

What would be the net charge of an atom if it had 11 protons, 12 neutrons, and 10 electrons?

The net charge would be +1.The number of protons (positive charges) is 11, and the number of electrons (negative charges) is 10. The net charge is 11 - 10 = +1. Neutrons do not contribute to the charge.

ChemistryClass 11CBSE

Why is the phrase 'Atomic number determines the element' a fundamental concept in chemistry?

This phrase is fundamental because the atomic number, which is the number of protons, uniquely defines an element's identity and its chemical properties. Any change in the number of protons results in a different element.

ChemistryClass 11CBSE

If an atom has 6 protons, 6 neutrons, and 6 electrons, what is its atomic number and mass number?

Atomic number = 6, Mass number = 12.Atomic number is the number of protons (6). Mass number is the sum of protons and neutrons (6 + 6 = 12).

ChemistryClass 11CBSE

Describe the general arrangement of subatomic particles within an atom, including their relative positions.

An atom consists of a dense, positively charged nucleus at its center, composed of protons and neutrons. Negatively charged electrons orbit this nucleus in a cloud-like region.The atomic model describes a central nucleus containing protons and neutrons, which accounts for most of the atom's mass and positive charge. Electrons, with their much smaller mass and negative charge, occupy the vast space surrounding the nucleus.

ChemistryClass 11CBSE

In a neutral atom, if there are 15 protons, how many electrons are present?

There are 15 electrons present.For a neutral atom, the number of positively charged protons must equal the number of negatively charged electrons to balance the overall charge.

ChemistryClass 11CBSE

What would be the effect on an atom's atomic number if it gained or lost neutrons?

Gaining or losing neutrons would not affect an atom's atomic number, as the atomic number is determined solely by the number of protons.The atomic number is fixed by the number of protons. Changing the number of neutrons only changes the mass number and creates an isotope of the same element, it does not change the element's identity or its atomic number.

ChemistryClass 11CBSE

Why is the mass of electrons generally disregarded when calculating the overall mass of an atom?

The mass of electrons is generally disregarded because it is extremely small, approximately 1/1836th the mass of a proton or neutron, making its contribution to the atom's total mass negligible.The vast majority of an atom's mass comes from its protons and neutrons. While electrons do have mass, it's so tiny in comparison that it doesn't significantly impact the overall atomic mass, especially when calculating the mass number.

ChemistryClass 11CBSE

If two atoms have the same number of protons but different numbers of neutrons, what are they called?

They are called isotopes.Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number. All isotopes of a given element have the same number of protons.

ChemistryClass 11CBSE

An atom has an atomic number of 17 and a mass number of 35. How many neutrons does it have?

The atom has 18 neutrons.Number of neutrons = Mass number - Atomic number. So, 35 - 17 = 18 neutrons.

ChemistryClass 11CBSE

What is the significance of the nucleus in an atom, considering the location of protons and neutrons?

The nucleus is the dense, central part of an atom where almost all of its mass is concentrated, due to the presence of protons and neutrons. It also contains all of the atom's positive charge.The nucleus is the heart of the atom, containing the heavy protons and neutrons. It accounts for virtually all of the atom's mass and its entire positive charge, which attracts the orbiting electrons.

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