Food Chemistry: Properties of Water
48 Questions
0 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the main reason for the high dielectric constant of water?

  • The high coordination number in liquid water.
  • The formation of hydrated H3O+ ions.
  • The presence of strong hydrogen bonds that can be transferred between molecules. (correct)
  • The ability of water molecules to rapidly form and break hydrogen bonds.

    • What is the approximate dissociation energy of a strong hydrogen bond in a hydrated H3O+ ion?

  • 100 kJ/mol (correct)
  • 50 kJ/mol
  • 10 kJ/mol
  • 200 kJ/mol

    • What is the average number of nearest neighbors for water molecules in ice?

  • 3
  • 4 (correct)
  • 2
  • 6

    • What is the approximate O-H~~~O distance in ice?

    <p>0.276 nm (C)</p> Signup and view all the answers

    What is the approximate H-O-H bond angle in ice?

    <p>109.5 degrees (D)</p> Signup and view all the answers

    Which of the following statements about proton transport in water is TRUE?

    <p>Protons jump between neighboring water molecules at high speeds. (D)</p> Signup and view all the answers

    Which of the following factors contribute to the difference in coordination number between liquid water and ice?

    <p>The different bond angles in liquid water and ice. (C)</p> Signup and view all the answers

    Which of the following statements about the structure of ice is TRUE?

    <p>Ice has a more open structure than liquid water due to the formation of hydrogen bonds. (D)</p> Signup and view all the answers

    What is a common example of a chemical compound containing water of hydration?

    <p>Na2SO4.10H2O (A)</p> Signup and view all the answers

    What is the primary method used for moisture determination, as mentioned in the text?

    <p>Loss on Drying (D)</p> Signup and view all the answers

    What factors influence the moisture content determined by the loss on drying method?

    <p>All of the above (D)</p> Signup and view all the answers

    Which of the following is NOT a method of moisture determination by loss on drying, as mentioned in the text?

    <p>Chemical reaction (C)</p> Signup and view all the answers

    In the distillation technique for moisture determination, what type of solvent is used?

    <p>Immiscible with water (C)</p> Signup and view all the answers

    Which of the following are examples of distillation procedures used for moisture determination?

    <p>Direct distillation and reflux distillation (B)</p> Signup and view all the answers

    What is the well-known chemical reaction method used for moisture determination, as mentioned in the text?

    <p>Karl Fischer titration (B)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of the distillation technique for moisture determination?

    <p>Requires a vacuum oven (A)</p> Signup and view all the answers

    What is the bond angle of the O-H covalent bonds in a water molecule?

    <p>104.5 degrees (C)</p> Signup and view all the answers

    What elements make up a water molecule?

    <p>1 oxygen and 2 hydrogen atoms (D)</p> Signup and view all the answers

    Which hybridization occurs in the oxygen atom of a water molecule?

    <p>sp3 (D)</p> Signup and view all the answers

    How many non-bonding electron pairs are associated with the oxygen in a water molecule?

    <p>Two (D)</p> Signup and view all the answers

    What is the effect of water's ionic character on its covalent bonds?

    <p>It introduces partial charges within the molecule. (B)</p> Signup and view all the answers

    What primarily influences the chemical and microbiological deterioration of foods?

    <p>Water content (B)</p> Signup and view all the answers

    The structure of the water molecule can be described as what geometric shape?

    <p>Pyramidal (B)</p> Signup and view all the answers

    What percentage of ionic character does the O-H bond in water possess?

    <p>40% (C)</p> Signup and view all the answers

    Which method is highly suitable for determining moisture in low-moisture foods like dried fruits and chocolate?

    <p>Direct distillation (C)</p> Signup and view all the answers

    What is the primary chemical reaction involved in moisture determination by chemical reaction?

    <p>2H2O + SO2 + I2 → C5H2SO4 + 2HI (A)</p> Signup and view all the answers

    What does KFReq stand for in the context of moisture determination?

    <p>Karl Fischer reagent moisture equivalence (C)</p> Signup and view all the answers

    How is the moisture content percentage expressed after determining KFReq?

    <p>%H2O = (KFReq × Ks) / S (A)</p> Signup and view all the answers

    What is the primary benefit of using the moisture determination chemical reaction method?

    <p>It offers accurate moisture content determination in low-moisture foods. (A)</p> Signup and view all the answers

    Which of the following methods is NOT mentioned as a moisture determination technique?

    <p>Verifiable chromatography (D)</p> Signup and view all the answers

    Which food products are particularly challenging to analyze for moisture using conventional methods?

    <p>Low-moisture foods high in sugar or protein (C)</p> Signup and view all the answers

    What type of analysis does not apply to moisture determination methods discussed?

    <p>Gas chromatography (D)</p> Signup and view all the answers

    What causes ice to be less dense than liquid water?

    <p>The formation of hydrogen bonds (C)</p> Signup and view all the answers

    What is the density of ice compared to water?

    <p>Ice is less dense than water (A)</p> Signup and view all the answers

    Which statement is true about free water in food products?

    <p>It acts as a solvent for salts and a dispersing agent (D)</p> Signup and view all the answers

    Which form of water in foods is held tightly to proteins?

    <p>Adsorbed water (A)</p> Signup and view all the answers

    What factor influences the choice of method for measuring moisture content in food products?

    <p>The expected moisture content of the food (C)</p> Signup and view all the answers

    What characterizes the water structure in liquid form?

    <p>It constantly forms and breaks hydrogen bonds (B)</p> Signup and view all the answers

    Which statement accurately describes the coordination number and density relationship?

    <p>Lower coordination number leads to lower density (C)</p> Signup and view all the answers

    Which property of water explains its lower viscosity?

    <p>The presence of hydrogen bonds (B)</p> Signup and view all the answers

    What is the primary advantage of controlling water activity in food products?

    <p>To extend the shelf life of the food (A)</p> Signup and view all the answers

    Which preservation method is most effective for increasing the shelf life of a food product with a high water activity (aw) of 0.95?

    <p>Adding salt (C)</p> Signup and view all the answers

    How does the moisture sorption isotherm relate to food stability?

    <p>It describes the relationship between water activity and moisture content (C)</p> Signup and view all the answers

    Which method is NOT effective for reducing water activity in dried fruits?

    <p>Storing in a humid environment (B)</p> Signup and view all the answers

    What combination of water loss and solid gain is associated with a candying process?

    <p>Minimal water removal and high solute penetration (B)</p> Signup and view all the answers

    What is a common misconception about food preservation methods?

    <p>Freezing eliminates all bacteria in food (C)</p> Signup and view all the answers

    Which statement correctly describes the balancing act of water activity in food processing?

    <p>Solute penetration should be maximized without losing too much water (D)</p> Signup and view all the answers

    What is one function of moisture sorption isotherms in food science?

    <p>To assess the equilibrium moisture content at specific water activity levels (D)</p> Signup and view all the answers

    Study Notes

    Food Chemistry and Analysis

    • Course code: BWD22303
    • Instructor: Assoc. Prof. ChM Dr. Norhayati Binti Muhammad
    • University: Universiti Tun Hussein Onn Malaysia
    • Department: Technology and Natural Resources, Faculty of Applied Sciences and Technology

    Water

    • Water is the predominant component in many foods.
    • Understanding water's properties and behavior are crucial due to its importance.
    • Water influences chemical and microbiological deterioration of food.
    • Table 0.1 displays the moisture content of various foods.

    4.1 Fundamental Properties and Structure of Water

    • Water (moisture) is the predominant constituent in many foods.
    • Factors like water content, properties, and behavior greatly influence food.
    • Important for understanding chemical and microbiological deterioration.

    4.1. Fundamental Properties and Structure of Water, Specific Properties

    • Vapor pressure (mm Hg) at various temperatures
    • Density (g/cm³) at various temperatures
    • Specific heat (cal/g°C) at various temperatures
    • Heat of vaporization (cal/g) at various temperatures
    • Thermal conductivity (kcal/m²h°C) at various temperatures
    • Surface tension (dynes/cm) at various temperatures
    • Viscosity (centipoises) at various temperatures
    • Refractive index at various temperatures
    • Dielectric constant at various temperatures
    • Coefficient of thermal expansion x 10⁻⁴ at various temperatures

    4.1. Fundamental Properties and Structure of Ice

    • Vapor pressure (mm Hg) at various temperatures
    • Heat of fusion (cal/g)
    • Heat of sublimation (cal/g)
    • Density (g/cm³) at various temperatures
    • Specific heat (cal/g°C) at various temperatures
    • Coefficient of thermal expansion x 10⁻⁵ at various temperatures
    • Heat capacity (joule/g)

    4.1. Fundamental Properties and Structure of Water Molecule

    • A water molecule is composed of one oxygen atom and two hydrogen atoms.
    • Oxygen has six valence electrons.
    • The six valence electrons of oxygen are hybridized to sp³ orbitals.
    • Two hybrid orbitals form O-H bonds with a bond angle of 104.5°, and the remaining two orbitals hold the non-bonding electron pairs.
    • The O-H covalent bonds have a partial (40%) ionic character.

    4.1 Fundamental Properties and Structure of Liquid Water & Ice

    • H-bridges result in significant differences between liquid water and ice.
    • In liquid water, the coordination number is higher (compared with ice).
    • Differences in bond angle and coordination number cause different densities in liquid water and ice.

    4.3 Moisture Determination By Loss On Drying

    • Primary method for moisture determination.
    • Sample is heated under set conditions, and weight loss calculates moisture content
    • Oven drying, vacuum oven, microwave analyzer are commonly used methods

    4.3 Moisture Determination By Distillation

    • Moisture co-distillation technique using a high boiling-point solvent
    • Direct Distillation and Reflux Distillation are common procedures used

    4.3 Moisture Determination By Chemical Reaction

    • Karl Fisher Titration method is crucial for determining water content.
    • Equation for Moisture Determination by Chemical Reaction
    • KFReq is calculated to determine the moisture equivalence

    4.4 Direct and Indirect Moisture Method

    • Dielectric Method
    • Hydrometer
    • Pycnometer
    • Refractometer
    • Infrared Analysis
    • Freezing Point

    4.2 Water Activity and Food Stability

    • Water activity (a) is a measure of water's energy status in a system.
    • Higher activity (a) means water has more energy, leading to various reactions and more microbial activity
    • a = p/p0 (Vapor pressure of water above sample at X °C) / (Vapor pressure of Pure Water at X °C)
    • Water activity and moisture content affect each other.
    • Various applications of water activity, like controlling microbial growth, controlling moisture migration and avoiding caking.

    Additional notes

    • Osmotic dehydration: Adding solute to food products can cause water outflow from the product to the environment, leading to different combinations (dewatering, etc).
    • Moisture Sorption Isotherm: The relationship between water activity (a) and moisture content, critical for understanding food stability.
    • Microbial Growth: Water activity affects microbial growth, and suitable water activity values prevent undesirable microbial activity.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Related Documents

    BWD22303 Food Chemistry and Analysis PDF

    Description

    This quiz explores the fundamental properties and structure of water as it relates to food chemistry. It covers essential concepts such as water content, behavior, and its impact on the chemical and microbiological deterioration of food. Ideal for students studying food science and analysis.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser