EXAM 1: Chemistry Of Water Flashcards
What is the definition of heat
Also known as energy
The movement of molecules
-> unit: calorie
What is a calorie
The amount of energy required to raise the temperature by 1 degree C
What is the earths most abundant and important solvent
Water!!!
How many bonds can H2O form
Up to four bonds
Polar covalent bonds (they are weak)
What is the temperature range of water in the liquid state
39 degrees F to 212 degrees F
This wide range indicates that water has a high specific heat
What is specific heat
The amount of energy to raise 1 gram of a substance 1 degree celcius
What does freezing point mean
Temperature at which a liquid becomes a solid
What is the freezing point of water
0 degrees celcius or 32 F
At what temperature does an organized bonding pattern emerge in water
4 degrees C
At what temperature does a lattice work of molecules in their tetrahedron formation
0 degrees celcius
What is the definition of boiling point
Temperature at which a liquid boils and becomes a gas
What temperature is the boiling point of water
212 F or 100 C
How much energy is added to convert water to steam?
540 calories
What is a factor that effects freezing point
Solutes alter the temperature water freezes and the time it takes a substance (e.g., foods) to freeze
How does salt effect freezing point
It lowers the temperature in which water will freeze and decreases freezing points of water
32 degrees -> -21 degrees F
How is freezing point effected in making frozen desserts
Sugar and fats interfere with ice crystal formation
What are two examples of how air pressure alters boiling point
Pressure cooker (increased air pressure)
- increases the temperature at which foods are cooked
Altitude (decreased air pressure)
- the boiling point decreases one degree celcius for every 960 ft
How do solutes effect boiling point
Salt and sugar:
- as sucrose concentration increases so does boiling point
Salt also increases the boiling point of water
Is water polar or nonpolar
Polar
What is free water
Free water is the largest amount of water present in foods and is easily separated from the food
Ex: the free water found in fruits
What is bound water
Bound water is incorporated into the chemical structure of other nutrients such as carbohydrates, fats and proteins
Bound water isn’t easily removed and is resistant to freezing or drying
Also not readily available to act as a medium for dissolving salts, acids or sugars
Ex: bread
What determines if water is hard or soft
The minerals in water determine this
What does hard water
Greater concentration of calcium and magnesium compounds
What does soft water mean
Higher sodium concentration
What are the functions of water in food
Heat transfer
Solvent
Chemical reactions
Removing water from foods is an example of preservation as it
Stops the growth of microorganisms as without water bacteria cannot survive
Water can also be used for preservation by
Washing away dirt and other debris
Preventing dehydration (rain showers in supermarket)
What is water activity
A measure of the amount of available (free) water in foods
What is the range of water activity
0 to the highest value 1.00, which is pure water
Most foods do not support bacterial growth if their aw is below…
0.85
This is why foods higher in water content are more prone to microbial spoilage
