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Consider the data shown below for a number of simple hydrides - Leaving Cert Chemistry - Question 11 - 2020
Question 11
Consider the data shown below for a number of simple hydrides. Hydride formula | Hydride name | Boiling point (°C) | Relative molecular mass --- ... show full transcript
Worked Solution & Example Answer:Consider the data shown below for a number of simple hydrides - Leaving Cert Chemistry - Question 11 - 2020
Step 1
Step 2
Describe, with the aid of a diagram, how hydrogen bonding arises between water molecules.
Answer
Water molecules exhibit a dipolar nature, with partial positive charges on hydrogen atoms and a partial negative charge on the oxygen atom. The diagram illustrating this shows the oxygen atom bearing a charge of 6- while the hydrogen atoms bear a charge of 6+. This polarization allows the hydrogen of one water molecule to form a hydrogen bond with the oxygen of another water molecule, resulting in a stable interaction.
Step 3
Why is water the only hydride in the table that exhibits strong hydrogen bonding?
Answer
Water contains small and highly electronegative oxygen, which facilitates hydrogen bonding. In contrast, other hydrides listed do not possess such a significant difference in electronegativities, as larger atoms like sulfur, selenium, and tellurium provide weaker interactions in comparison.
Step 4
Why is the boiling point of hydrogen selenide higher than that of hydrogen sulfide?
Answer
Hydrogen selenide (H₂Se) has larger molecular size and stronger van der Waals interactions compared to hydrogen sulfide (H₂S). The increased molecular weight of H₂Se contributes to stronger intermolecular forces, resulting in a higher boiling point.
Step 5
Explain why, although carbon and selenium have the same electronegativity value, CH₄ is almost completely insoluble in water and H₂Se is highly soluble in water.
Answer
Methane (CH₄) is a nonpolar molecule and thus does not interact favorably with polar water molecules. Conversely, hydrogen selenide (H₂Se) is polar, allowing it to engage in dipole-dipole interactions with water. The presence of these interactions gives H₂Se its greater solubility in water compared to CH₄.