Preparation and Properties of Hydrogen, Oxygen, Nitrogen and Carbon dioxide, Oxidation and Reduction
Preparation and Properties of Hydrogen, Oxygen, Nitrogen and Carbon dioxide, Oxidation and Reduction MCQ Questions
1.
Hydrogen is the most abundant element in the universe and is placed at the top of the periodic table because it resembles:
A.
The noble gases (Group 18)
B.
Only the halogens (Group 17)
C.
Only the alkali metals (Group 1)
D.
Both alkali metals and halogens, depending on the property considered
ANSWER :
D. Both alkali metals and halogens, depending on the property considered
Approach
The question asks about the placement of hydrogen in the periodic table, specifically regarding its resemblance to other groups. Hydrogen is unique due to its electronic configuration and properties, exhibiting characteristics of both alkali metals and halogens.
Step-by-step
- Electronic Configuration: Hydrogen has one electron in its outermost shell (\(1s^1\)). This configuration is similar to alkali metals (Group 1), which also have one valence electron (\(ns^1\)).
- Tendency to Lose an Electron: Like alkali metals, hydrogen can lose its single electron to form a positive ion (\(H^+\)). For example, in acids.
- Tendency to Gain an Electron: Hydrogen can also gain an electron to achieve a stable duplet configuration (\(1s^2\)), forming a hydride ion (\(H^-\)). This behavior is similar to halogens (Group 17), which gain one electron to complete their octet (\(ns^2 np^5 \rightarrow ns^2 np^6\)).
- Formation of Covalent Bonds: Hydrogen readily forms covalent bonds by sharing its electron, a property not typical of either alkali metals (which prefer ionic bonds) or halogens (which can form both ionic and covalent bonds).
- Diatomic Nature: Hydrogen exists as a diatomic molecule (\(H_2\)), similar to halogens (\(F_2, Cl_2\), etc.), but unlike alkali metals which are monatomic.
- Position in the Periodic Table: Due to these dual characteristics, hydrogen's placement is often debated. It is typically placed at the top of Group 1 but is sometimes also shown separately or above Group 17, reflecting its unique nature and resemblance to both groups depending on the chemical context.
Correct Option: D) Both alkali metals and halogens, depending on the property considered. Hydrogen exhibits properties similar to alkali metals (e.g., forming \(H^+\) ion, having one valence electron) and halogens (e.g., forming \(H^-\) ion, existing as a diatomic gas). Its unique position reflects this dual nature.
Incorrect Options
- A) The noble gases (Group 18) — Hydrogen does not resemble noble gases. Noble gases have a stable electron configuration (duplet or octet) and are largely unreactive, whereas hydrogen is highly reactive and has an incomplete shell.
- B) Only the halogens (Group 17) — While hydrogen shares some properties with halogens (e.g., forming \(H^-\), diatomic nature), it also shares significant properties with alkali metals. Therefore, stating "only" halogens is incorrect.
- C) Only the alkali metals (Group 1) — While hydrogen shares some properties with alkali metals (e.g., forming \(H^+\), one valence electron), it also shares significant properties with halogens. Therefore, stating "only" alkali metals is incorrect.
2.
On Earth, hydrogen is rarely found in the free (elemental) state and mostly occurs in the combined state, most abundantly as a constituent of:
Approach
The question asks about the most abundant form in which hydrogen is found in a combined state on Earth. We need to identify which of the given options contains hydrogen and is present in large quantities.
Step-by-step
- Understand the nature of hydrogen: Hydrogen is the lightest and most abundant element in the universe. However, on Earth, due to its low atomic mass and high reactivity, it rarely exists as a free element (\(H_2\)) in significant quantities. Instead, it readily combines with other elements.
- Evaluate the options for hydrogen content:
- Common salt: Common salt is primarily sodium chloride (\(NaCl\)). It does not contain hydrogen.
- Metal ores: Metal ores are rocks or minerals from which metals can be extracted. While some ores might contain water of hydration or hydroxyl groups, hydrogen is not their primary constituent, nor is it the most abundant combined form of hydrogen.
- Limestone: Limestone is primarily calcium carbonate (\(CaCO_3\)). It does not contain hydrogen.
- Water: Water has the chemical formula \(H_2O\). It is composed of two hydrogen atoms and one oxygen atom.
- Consider abundance: Water covers about 71% of the Earth's surface and is essential for all known forms of life. It is by far the most abundant compound on Earth that contains hydrogen.
- Conclusion: Given its chemical composition and widespread presence, water is the most abundant constituent containing hydrogen in a combined state on Earth.
Correct Option:
D) Water — Water (\(H_2O\)) is a compound of hydrogen and oxygen. It is extremely abundant on Earth, covering most of its surface and present in the atmosphere, underground, and in living organisms. Therefore, hydrogen is most abundantly found in the combined state as a constituent of water.
Incorrect Options
- A) Common salt — Common salt is sodium chloride (\(NaCl\)). It does not contain hydrogen.
- B) Metal ores — Metal ores are typically compounds of metals with oxygen, sulfur, or carbonates, e.g., iron oxides, copper sulfides. While some might contain trace amounts of water or hydroxyl groups, they are not the primary or most abundant form of combined hydrogen on Earth.
- C) Limestone — Limestone is primarily calcium carbonate (\(CaCO_3\)). It does not contain hydrogen.
3.
The three naturally occurring isotopes of hydrogen are:
A.
Protium, helium and tritium
B.
Protium, deuterium and tritium
C.
Protium, deuterium and neon
D.
Deuterium, oxygen and tritium
ANSWER :
B. Protium, deuterium and tritium
Approach
The question asks to identify the three naturally occurring isotopes of hydrogen. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Hydrogen is the first element in the periodic table, and its isotopes are fundamental concepts in chemistry.
Step-by-step
- Understand Isotopes: Isotopes are variants of a particular chemical element which differ in neutron number, and consequently in nucleon number (mass number). All isotopes of a given element have the same number of protons.
- Recall Hydrogen's Atomic Structure: Hydrogen (\(Z=1\)) always has one proton. Its isotopes differ in the number of neutrons.
- Identify Hydrogen Isotopes:
- Protium (\(^{1}\text{H}\) or H): This is the most common isotope of hydrogen, making up over 99.98% of natural hydrogen. It has one proton and no neutrons.
- Deuterium (\(^{2}\text{H}\) or D): This isotope has one proton and one neutron. It is also known as "heavy hydrogen."
- Tritium (\(^{3}\text{H}\) or T): This isotope has one proton and two neutrons. It is radioactive and has a relatively short half-life.
- Compare with Options: Check which option correctly lists these three isotopes.
Correct Option: B) Protium, deuterium and tritium are the three naturally occurring isotopes of hydrogen. Protium has 0 neutrons, Deuterium has 1 neutron, and Tritium has 2 neutrons, all having 1 proton.
Incorrect Options
- A) Protium, helium and tritium — Helium is a different element (atomic number 2), not an isotope of hydrogen.
- C) Protium, deuterium and neon — Neon is a different element (atomic number 10), not an isotope of hydrogen.
- D) Deuterium, oxygen and tritium — Oxygen is a different element (atomic number 8), not an isotope of hydrogen.
4.
Which isotope of hydrogen is radioactive?
B.
None of the isotopes are radioactive
Approach
The question asks to identify the radioactive isotope of hydrogen. We need to recall the common isotopes of hydrogen and their properties, specifically their stability and radioactivity.
Step-by-step
- Understand Isotopes: Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers.
- Identify Hydrogen Isotopes: Hydrogen has three main isotopes:
- Protium (\(^{1}\text{H}\)): Contains 1 proton and 0 neutrons. It is the most common and stable isotope.
- Deuterium (\(^{2}\text{H}\) or \(\text{D}\)): Contains 1 proton and 1 neutron. It is also a stable isotope, often called "heavy hydrogen."
- Tritium (\(^{3}\text{H}\) or \(\text{T}\)): Contains 1 proton and 2 neutrons. This isotope is unstable.
- Determine Radioactivity: Radioactivity is the property of unstable atomic nuclei to spontaneously emit radiation as they decay into more stable forms. Among the three isotopes of hydrogen, Tritium is known to be unstable and undergoes beta decay, making it radioactive.
Correct Option: C) Tritium is the radioactive isotope of hydrogen. It has a half-life of approximately 12.32 years and decays by emitting a low-energy beta particle to become Helium-3.
Incorrect Options
- A) Deuterium — Deuterium is a stable isotope of hydrogen, containing one proton and one neutron. It is not radioactive.
- B) None of the isotopes are radioactive — This statement is incorrect because Tritium is a radioactive isotope of hydrogen.
- D) Protium — Protium is the most common and stable isotope of hydrogen, containing one proton and no neutrons. It is not radioactive.
5.
Heavy water, used as a moderator in nuclear reactors, has the chemical formula:
Approach
The question asks for the chemical formula of heavy water, which is used as a moderator in nuclear reactors. This requires knowledge of the composition of heavy water.
Step-by-step
- Understand the term "heavy water": Heavy water is a form of water that contains a higher proportion of the hydrogen isotope deuterium (\(D\)) rather than the common hydrogen isotope protium (\(H\)).
- Identify the isotopes: Protium (\(^{1}H\)) has one proton and no neutrons. Deuterium (\(^{2}H\), often denoted as \(D\)) has one proton and one neutron. Tritium (\(^{3}H\), often denoted as \(T\)) has one proton and two neutrons.
- Recall the chemical formula of water: Ordinary water has the chemical formula \(H_2O\), meaning two hydrogen atoms bonded to one oxygen atom.
- Derive the formula for heavy water: Since heavy water replaces protium with deuterium, its chemical formula will be \(D_2O\).
- Role in nuclear reactors: Heavy water (\(D_2O\)) is used as a moderator in nuclear reactors because deuterium has a very low neutron capture cross-section, meaning it absorbs fewer neutrons than protium, allowing for a more efficient chain reaction.
Correct Option:
D) D2O is the correct chemical formula for heavy water. It consists of two deuterium atoms and one oxygen atom.
Incorrect Options
- A) H2O2 — This is the chemical formula for hydrogen peroxide, a compound with strong oxidizing properties, not heavy water.
- B) T2O — This would be "tritiated water" or "super-heavy water," where hydrogen is replaced by tritium. While tritium is an isotope of hydrogen, \(T_2O\) is not what is commonly referred to as "heavy water" in the context of nuclear reactors. Heavy water specifically refers to deuterium oxide.
- C) H2O — This is the chemical formula for ordinary water (light water), which contains the most common isotope of hydrogen, protium. While it can also act as a moderator, it is less efficient than heavy water due to its higher neutron absorption cross-section.
6.
The most common isotope of hydrogen, having a nucleus with just one proton and no neutron, is called:
Approach
The question asks to identify the most common isotope of hydrogen that has a nucleus with one proton and no neutron. We need to recall the definitions and compositions of various hydrogen isotopes.
Step-by-step
- Understand Isotopes: Isotopes are atoms of the same element (same number of protons) but with different numbers of neutrons.
- Recall Hydrogen's Atomic Number: Hydrogen (\(H\)) has an atomic number of 1, meaning every hydrogen atom has exactly one proton in its nucleus.
- Analyze the given description: The question describes an isotope of hydrogen with "just one proton and no neutron" in its nucleus.
- Identify Hydrogen Isotopes:
- Protium (\(^{1}H\)): This is the most common isotope of hydrogen. Its nucleus consists of one proton and zero neutrons. Its mass number is 1.
- Deuterium (\(^{2}H\) or \(D\)): This isotope has one proton and one neutron in its nucleus. Its mass number is 2. It is also known as "heavy hydrogen."
- Tritium (\(^{3}H\) or \(T\)): This isotope has one proton and two neutrons in its nucleus. Its mass number is 3. It is radioactive.
- Match the description: The description "one proton and no neutron" perfectly matches the composition of Protium.
Correct Option: B) Protium is the most common isotope of hydrogen, characterized by a nucleus containing one proton and no neutrons.
Incorrect Options
- A) Deuterium — Deuterium has one proton and one neutron in its nucleus, making its mass number 2. It is not the most common isotope.
- C) Tritium — Tritium has one proton and two neutrons in its nucleus, making its mass number 3. It is a radioactive isotope and is very rare.
- D) Positronium — Positronium is not an isotope of hydrogen. It is an exotic atom composed of an electron and a positron (the antiparticle of the electron), which are bound together.
