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Chapter 7: Problem 31

Identify the correct statements : (a) Mass of H-atom is \(1.66 \times 10^{-27} \mathrm{~kg}\). (b) Cu dissolves in \(\mathrm{H}_{2} \mathrm{SO}_{4}\) and liberates \(\mathrm{H}_{2}\). (c) \(\mathrm{H}_{2}\) is liberated by the action of \(\mathrm{Al}\) with conc. \(\mathrm{NaOH}\). (d) Hydrogen contains at room temperature \(25 \%\) para and \(75 \%\) ortho form.

Short Answer

Expert verified
Correct statements: (a) and (c).

Step by step solution

01

Analyze Statement (a)

The mass of a hydrogen atom is approximately \(1.66 \times 10^{-27} \text{ kg}\). This value is close to the expected atomic mass of a proton, which matches the mass of a hydrogen atom because hydrogen typically only has one proton (and virtually no neutrons). This statement is correct.
02

Analyze Statement (b)

Copper (Cu) does not react with dilute sulfuric acid \((\mathrm{H}_2\mathrm{SO}_4)\) to liberate hydrogen gas \((\mathrm{H}_2)\) because copper is below hydrogen in the reactivity series and does not displace hydrogen from the acid under normal conditions. This statement is incorrect.
03

Analyze Statement (c)

When aluminum \((\mathrm{Al})\) reacts with concentrated sodium hydroxide \((\mathrm{NaOH})\), it forms sodium aluminate and hydrogen gas \((\mathrm{H}_2)\) is liberated. This can be represented by the chemical equation: \(2\mathrm{Al} + 2\mathrm{NaOH} + 6\mathrm{H}_2\mathrm{O} \rightarrow 2\mathrm{NaAl(OH)}_4 + 3\mathrm{H}_2\). This statement is correct.
04

Analyze Statement (d)

At room temperature, hydrogen gas exists as a mixture of two isomeric forms: ortho and para hydrogen, but the typical distribution is approximately 75% ortho-hydrogen and 25% para-hydrogen, not the other way around. This statement is incorrect.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Atomic Mass
Atomic mass is a fundamental concept in chemistry, indicating the mass of an atom primarily due to its protons and neutrons. For hydrogen, the simplest element, its atomic mass is often approximately equal to the mass of a single proton because it typically contains no neutrons. When you hear that a hydrogen atom has a mass of about \(1.66 \times 10^{-27} \text{ kg}\), it's a reflection of this simplicity. The tiny mass number signifies the lightest atomic structure, helping in calculations across chemical reactions.
  • The atomic mass unit (amu) is another way to express this mass, where hydrogen's atomic mass is approximately 1 amu.
  • Calculating atomic mass is crucial for understanding molecular weights, which influences chemical formulas and reaction stoichiometry.
The idea of atomic mass sets the stage for exploring more complex elements, impacting how atoms bond and interact in the broad realm of chemistry.
Reactivity Series
The reactivity series is a tool used by chemists to rank metals by their reactivity with other substances, such as acids or water. Essentially, it helps predict how metals will behave in chemical reactions. In the context of our problem, understanding why copper doesn't react with sulfuric acid involves its position in this series. Copper, being less reactive than hydrogen, sits below it.
  • Reactivity series is typically organized from most reactive (like potassium) to least reactive (like gold).
  • It helps in predicting whether a metal will displace another in a compound, as seen in displacement reactions.
Knowing this helps avoid unnecessary reactions and understand why certain metals are chosen for specific reactions or applications.
Chemical Reactions
Chemical reactions describe how substances interact to form new compounds. In our exercise, the reaction between aluminum and sodium hydroxide illustrates a specific type of chemical interaction. Here, we see aluminum reacting with concentrated \(\mathrm{NaOH}\) to release hydrogen gas and form sodium aluminate.
  • This process exemplifies a double displacement reaction, where elements from two different compounds exchange places.
  • Equations for reactions must always be balanced to follow the law of conservation of mass.
  • This law indicates that atoms are neither created nor destroyed in chemical reactions, affecting only their arrangements.
Such principles guide chemists in synthesizing new materials and understanding energy changes within reactions.
Isomeric Forms
Isomers are compounds that share the same molecular formula but differ in structure, affecting properties and behavior. Hydrogen exhibits this through its ortho and para forms, which are spin isomers, differing by the orientation of the nuclear spins of the molecules.
  • Ortho-hydrogen has parallel spins and is more thermodynamically stable at higher temperatures.
  • In contrast, para-hydrogen has anti-parallel spins and is more stable at lower temperatures.
  • The ratio of ortho to para hydrogen varies with temperature, commonly around 75% ortho to 25% para at room temperature.
These differences impact hydrogen's physical properties and behavior during reactions, particularly in cryogenic applications and nuclear processes.
Hydrogen Properties
Hydrogen is unique as the most abundant yet simplest element in the universe, composed of just one proton and one electron. Its lightweight and high reactivity make it highly versatile in chemistry.
  • It forms bonds easily, creating essential compounds like water and hydrocarbons.
  • Its diatomic form, \(\mathrm{H}_2\), is significant in reactions, acting as a reducing agent.
  • Hydrogen can also exist in atomic, ionic, and radical forms under different conditions, diversifying its use.
Understanding hydrogen's properties allows chemists to harness it for energy, environmental, and synthesis applications, showcasing its wide-reaching impact in both natural and industrial processes.

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Most popular questions from this chapter

Alkali metals form hydrated compounds. The hydration enthalpies of alkali metals are in the sequence of : (a) \(\mathrm{Rb}^{+}>\mathrm{Li}^{+}>\mathrm{Na}^{+}>\mathrm{K}^{+}>\mathrm{CS}^{+}\) (b) \(\mathrm{CS}^{+}>\mathrm{Rb}^{+}>\mathrm{K}^{+}>\mathrm{Na}^{+}>\mathrm{Li}^{+}\) (c) \(\mathrm{L}^{+}>\mathrm{Na}^{+}>\mathrm{K}^{+}>\mathrm{Rb}^{+}>\mathrm{CS}^{+}\) (d) \(\mathrm{K}^{+}>\mathrm{Na}^{+}>\mathrm{Li}^{+}>\mathrm{Rb}^{+}>\mathrm{CS}^{+}\)

Which of the following compounds is known as pearl ash? (a) \(\mathrm{KMnO}_{4}\) (b) \(\mathrm{K}_{2} \mathrm{CO}_{3}\) (c) KI (d) \(\mathrm{KOH}\)

\(\mathrm{BeF}_{2}\) is soluble in water whereas fluorides of other alkaline earth metals are insoluble because of : (a) ionic nature of \(\mathrm{BeF}_{2}\) (b) covalent nature of \(\mathrm{BeF}_{2}\) (c) greater hydration energy of \(\mathrm{Be}^{2+}\) ion (d) greater lattice enrgy of \(\mathrm{Be}^{2+}\) ion

\(\mathrm{Be}(\mathrm{OH})_{2}\) is : (a) acidic (b) basic (c) amphoteric (d) neutral

Which of the following hydrides does conduct electricity? (a) \(\mathrm{GeH}_{2}\) (b) \(\mathrm{SiH}_{4}\) (c) \(\mathrm{B}_{2} \mathrm{H}_{6}\) (d) \(\mathrm{NaH}\)
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