Questions and Answers
What is the term for molecules that are attracted to water?
Liquid mercury adheres to glass tubes due to the presence of charges.
False
What phenomenon occurs at the surface of water in measurement devices due to adhesion?
Meniscus
Hydrophilic molecules are often _____ in water if they are not too large.
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Match the terms with their definitions:
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Why should one keep their eye parallel to the bottom of the meniscus when taking measurements?
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Hydrophobic molecules can easily dissolve in water.
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What happens to water molecules near a glass surface?
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Which of the following statements about hydrophobic molecules is correct?
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Oil and water are miscible with each other.
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What type of molecules are described as 'water-liking'?
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Small and smallish hydrophilic molecules are __________ in water.
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Which ions can form hydration shells when mixed with water?
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Match the following terms with their descriptions:
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Water is effective at dissolving salts because it can dissociate into ions.
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What is formed around ions when they dissolve in water?
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Which of the following sugars is composed of glucose and fructose?
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Sugars such as glucose and sucrose are non-polar molecules.
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What happens to the solubility of polar molecules as their size increases?
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Starch is composed of many linked ________ molecules.
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Match the following types of bonds with their properties:
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What type of bonds are predominant in hydrophobic molecules?
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Water can dissolve all polar molecules regardless of their size.
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What characteristic do polar molecules have that affects their interaction with water?
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What pH level is characteristic of lemon juice?
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The pH of distilled water in equilibrium with the atmosphere is approximately 5.7.
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What process causes water to become acidic when CO2 is dissolved in it?
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The pH scale measures the concentration of _____ ions in a solution.
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Match the following substances with their respective pH levels:
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Which of the following bonds are considered important biological non-polar covalent bonds?
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Fats are hydrophilic due to their C-C and C-H bonds.
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What is the pH value of pure water?
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A strong acid shows almost complete dissociation and has a high concentration of [____].
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Match the following substances with their respective pH values:
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What is the formula for the dissociation of water?
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High acidity corresponds to a high concentration of hydroxyl ions [OH-].
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The equation for calculating pH is pH = -log[____].
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Study Notes
Adhesion of Water
- Water molecules are attracted to large polar or charged molecules, sticking to them despite not being able to dissolve them.
- Glass tubes attract water due to their charges, forming a meniscus in water measurement devices, while mercury, being non-polar, does not adhere to glass.
Meniscus and Measurement
- The meniscus occurs in water-based fluid measurement devices like burettes and graduated cylinders due to adhesion.
- Accurate volume readings require positioning the eye parallel to the bottom of the meniscus.
Hydrophilic vs. Hydrophobic
- Hydrophilic molecules are polar or charged and are attracted to water, often being soluble if they are not excessively large.
- Hydrophobic molecules consist mainly of non-polar covalent bonds, such as fats and oils, repelling water and forming droplets when mixed.
Solubility of Molecules
- Water effectively dissolves salts like NaCl, creating hydration shells around dissolved ions, aligning opposite charges of water molecules with charged ions.
- Small polar molecules, such as sugars (e.g., glucose, sucrose), are also soluble in water due to their polar covalent bonds that attract water.
Large Polar Molecules and Water
- The solubility of polar molecules decreases as size increases; large polar molecules do not dissolve in water despite being hydrophilic.
- Starch, a large polar molecule made of linked glucose units, exemplifies this phenomenon.
Properties of Hydrophobic Molecules
- Hydrophobic molecules lack significant polar regions, composed primarily of C–C and C–H bonds, making them repel water.
- Structural examples include triglycerides, which have limited polar bonds and are therefore hydrophobic.
Water Dissociation
- Water can dissociate into hydrogen ions (H+) and hydroxide ions (OH-), demonstrating reversible equilibrium.
- Strong acids, such as hydrochloric acid (HCl), exhibit complete dissociation in contrast to water's equilibrium.
Acidity and pH Measurement
- Acidity relates directly to the concentration of hydrogen ions, where high [H+] indicates high acidity (low pH) and vice versa for basicity (high pH).
- pH is calculated using the formula: pH = -log[H+]. Neutral pH is defined as 7, whereas values below and above indicate acidic and basic/alkaline solutions, respectively.
Influence of CO2 on pH
- CO2 reacts with water to form carbonic acid, contributing to increased acidity and affecting blood pH and aquatic ecosystems.
- The equilibrium involving CO2, H2CO3, HCO3-, and CO32- plays a critical role in biological processes and water chemistry.
Summary of Water as a Solvent
- The polar covalent nature of water characterizes it as a solvent for small polar and charged molecules, termed hydrophilic.
- The solubility of polar molecules decreases with size, while molecules composed mainly of C-H and C-C bonds remain insoluble and are hydrophobic, underscoring that water is not a universal solvent.
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Description
Explore the fascinating concept of water's adhesion properties and how it interacts with large polar and charged molecules. This quiz will test your understanding of these properties and their implications in various scientific contexts.
