Textbook Question
(c) Why do substances with high surface tension also tend to have high viscosities?
Ch.11 - Liquids and Intermolecular Forces
Chapter 11, Problem 36
Hydrazine (H2NNH2), hydrogen peroxide (HOOH), and water (H2O) all have exceptionally high surface tensions compared with other substances of comparable molecular weights. What structural property do these substances have in common, and how might that account for the high surface tensions?
Verified step by step guidance1
Step 1: Identify the structural property common to hydrazine (H2NNH2), hydrogen peroxide (HOOH), and water (H2O). All these molecules have hydrogen atoms bonded to highly electronegative atoms (nitrogen in hydrazine and oxygen in hydrogen peroxide and water).
Step 2: Recognize that the presence of hydrogen atoms bonded to electronegative atoms allows for hydrogen bonding. Hydrogen bonds are a type of strong dipole-dipole interaction that occurs between molecules.
Step 3: Explain that hydrogen bonding significantly increases the intermolecular forces between molecules. This is because hydrogen bonds are stronger than typical van der Waals forces, leading to a higher attraction between molecules.
Step 4: Relate the strong intermolecular forces due to hydrogen bonding to surface tension. Surface tension is the energy required to increase the surface area of a liquid, and stronger intermolecular forces result in higher surface tension.
Step 5: Conclude that the high surface tensions of hydrazine, hydrogen peroxide, and water are due to the presence of hydrogen bonding, which is a result of their structural property of having hydrogen atoms bonded to electronegative atoms.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hydrogen Bonding
Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is covalently bonded to highly electronegative atoms like oxygen or nitrogen. In hydrazine, hydrogen peroxide, and water, the presence of O-H or N-H bonds allows for extensive hydrogen bonding between molecules, which significantly increases their surface tension by creating a cohesive force that holds the molecules together.
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Molecular Polarity
Molecular polarity refers to the distribution of electrical charge over the atoms in a molecule. Polar molecules, such as water and hydrogen peroxide, have regions of partial positive and negative charges due to differences in electronegativity. This polarity enhances intermolecular attractions, contributing to higher surface tension as the molecules tend to stick together more strongly than nonpolar molecules.
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Surface Tension
Surface tension is the property of a liquid that causes its surface to behave like a stretched elastic membrane. It arises from cohesive forces between liquid molecules at the surface, which are stronger than those in the bulk due to fewer neighboring molecules. The high surface tension of hydrazine, hydrogen peroxide, and water is a direct result of their strong intermolecular forces, primarily due to hydrogen bonding and molecular polarity.
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Related Practice
Textbook Question
Based on their composition and structure, list CH2Cl2, CH3CH2CH3, and CH3CH2OH in order of (a) increasing intermolecular forces (c) increasing surface tension
Textbook Question
Liquids can interact with flat surfaces just as they can with capillary tubes; the cohesive forces within the liquid can be stronger or weaker than the adhesive forces between liquid and surface:
(b) Which of these diagrams, i or ii, rep- resents what happens when water is on a nonpolar surface?
Textbook Question
The boiling points, surface tensions, and viscosities of water and several alcohols are as shown below: (b) How do you explain the fact that propanol and ethylene glycol have similar molecular weights (60 versus 62 amu), yet the viscosity of ethylene glycol is more than 10 times larger than propa- nol?
Textbook Question
Name the phase transition in each of the following situations and indicate whether it is exothermic or endothermic: (c) Rubbing alcohol in an open container slowly disappears.