Water Flashcards
(38 cards)
What is special about water?
It can be found in all three states - gases, liquids and solid
Briefly describe what water is
Water is a polar, discrete compound.
How much does water cover the earths surface?
About 71%
What produces a continual supply of water?
The water cycle
What reactions of life is water involved with? And name the equations
Photosynthesis and respiration
Water is a reactant in photosynthesis and a product in respiration
The properties of water include
- high latent of fusion
- high latent f vapourisation
- high specific heat capacity
- high melting point
- higher density in liquid state than solid state
- expansion on freezing
Can water conduct electricity?
Pure water cannot conduct electricity whilst impure water can be an excellent conductor due to the presence of dissolved substances
Explain why water has a high melting and boiling temperature?
In an ice crystal, the water molecule is arranged in a structured and regular manner, with each molecule forming hydrogen bonds directly to four other molecules.
For ice to melt, energy must be provided to increase the KINETIC ENERGY of the water molecules to the point where they break free of the crystal lattice. In the melting process, some of the hydrogen bonds break as the ice structure collapses to produce liquid water, which is roughly 10% denser than ice.
Therefore, the relatively high melting point of water indicates that this process requires a relatively large amount of energy.
Why does water have a high BOILING TEMPERATURE?
When water is boiled, the water molecules are separated from each other and all the hydrogen bonds are broken. Water requires a significant amount of energy to overcome these relatively strong hydrogen bonds between its molecule.
What is the definition of latent heat of fusion
The latent heat if fusion is the amount of energy needed to changed a fixed amount of water from the solid to the liquid state at 0’C.
What’s the latent heat of vaporisation?
The amount of energy needed to change a fixed mass of water from the liquid to a gaseous state at 100’C.
What is the specific heat capacity
It’s the amount of energy needed to raise the temperature of one gram of water 1’C.
What is the specific capacity of water?
4.2 J g-1 ‘C -1
This means 4.2 joules of heat energy is needed to increase the temperature of 1 gram of water by 1’C
Explain expansion on freezing
When liquid water is cooled, molecules move more slowly. When liquid water is being frozen, molecules take up the typical arrangement in an ice crystal. Each water molecule forms hydrogen bonds to four close neighbors. This is a very open arrangement - the water molecules are more widely spread in ice.
Why can marine life survive in winter?
Because the density of the ice is less liquid water. The ice will float on water due to hydrogen bonding, providing an insulating layer that prevents the water below from freezing.
Why is water sometimes called universal solvent?
Water is an excellent solvent for many ionic and polar substances. This is due its polarity and ability to form hydrogen bonds. Water is therefore attracted to ions and polar substances.
Where do most biological processes occur?
In aqueous environment
What are the characteristics of a solution?
They are homogeneous (the solute and solvent cannot be distinguished from one another).
- the dissolved particles are too small to see
- the proportion of dissolved solute varies from one solution to another
What types of substances dissolve readily in water?
- ionic or polar covalent bindings
- polar covalent compounds that can form hydrogen bonds with water
- polar covalent molecular compounds that ionize
- ionic compounds
What is a solute
A substance that is dissolved in a solvent to make a solution
What does a dilute solution contain?
A small amount of solute
What are volumes of water containing dissolved substances called?
Aqueous solutions
What is water a good solvent for?
Polar covalent molecular and ionic solutes
Polar convalent compounds that can form hydrogen bonds with water
Substances such as sugar and ethanol can easily dissolve in water.
- ethanol molecules contain a polar O-H bond, so there are hydrogen bonds between the molecules in pure ethanol.
- hydrogen bonds between water and ethanol molecules are broken
- hydrogen bonds between water and ethanol molecules are formed.
