Flashcards in Water, Salts, Acids, Bases, pH, Buffers Deck (19)
Why is water called a polar molecule?
A water molecule, because of its shape, is a polar molecule. That is, it has one side that is positively charged and one side that is negatively charged. The molecule is made up of two hydrogen atoms (slight positive charge) and one oxygen atom (slight negative charge). The bonds between the atoms are called covalent bonds, because the atoms share electrons.
What are the four properties of water that make it so necessary for life?
1. Universal solvent
2. Ideal transport medium
3. High heat capacity and high heat vaporization
Define solvent/diluent, solute and solution
Solvent/Diluent = Liquid that can dissolve a substance (such as water)
Solute = Solid (such as a powder)
Solution = all completely dissolved (final mixture)
Water and ice
Ice is held by its hydrogen bonds in a crystal like structure in which each water molecule is bound together by 4 hydrogen bonds to other water molecules. These bonds are packed less tightly than they are in liquid water, so solid water is less dense than liquid water and therefore floats.
Water's high heat capacity
Water's high heat capacity make it a good temperature moderator. Water's heat capacity makes oceans, ponds, lakes, and other bodies of water relatively constant throughout the seasons.
Why is water a good solvent?
Because it's polar, it can rip things apart (anything that's ionicly bonded).
The polar properties of water make it a good solvent for polar molecules (e.g. sugars and alcohols), which form hydrogen bonds with the water molecules, and ionic compounds (e.g. salts, acids and bases) , which dissociate into their component ions.
Why is water a good transport medium?
Positive ends of the water molecule surround or blanket negatively charged molecules. This blanketing allows molecules to move around freely and to be cushioned from each other.
Water is a very important transport medium for living organisms because of its solvent properties and because it remains a liquid over a large range of temperatures.
What about water's high heat capacity and evaporation?
The molecules of water can absorb a lot of heat energy. Water has a very high thermal capacity. The hydrogen bonding forms a lattice which does not easily fall apart as the temperature rises.
Compared to molecules of similar size and properties water has a very high melting point and boiling point. Water is a very, thermally stable medium which helps living organisms resist changes in their environment.
To make water change from a liquid to a vapor requires a lot of energy. Evaporation of water on a the surface of a body cools it down significantly.
How is water used as a lubricant?
Water serves as a lubricant in digestion and almost all other body processes. The water in saliva facilitates chewing and swallowing, ensuring that foods will slide easily down the esophagus. Water in other digestive fluids sustains movement throughout the gastrointestinal system. The watery fluid surrounding such body parts as joints and eyeballs helps them move smoothly and is in fact their only lubricant.
Examples of salt
Salts are mineral compounds that have ionic bonds.
In their ionic form, they are known as electrolytes.
Two examples of salt:
- Sodium Chloride
- Calcium Phosphate
What happens when salt is added to water?
They immediately ionize, or divide into separate ions.
Define and give some examples of electrolytes
Substances that have the ability to transmit an electrical charge (acids and bases, for example).
Examples of strong electrolytes: potassium chloride, sodium hydroxide, sodium nitrate..
Atoms vs. ions
Atoms are neutral; they contain the same number of protons as electrons. By definition, an ion is an electrically charged particle produced by either removing electrons from a neutral atom to give a positive ion or adding electrons to a neutral atom to give a negative ion. When an ion is formed, the number of protons does not change.
Neutral atoms can be turned into positively charged ions by removing one or more electrons. A neutral sodium atom, for example, contains 11 protons and 11 electrons. By removing an electron from this atom we get a positively charged Na+ ion that has a net charge of +1.
Atoms that gain extra electrons become negatively charged. A neutral chlorine atom, for example, contains 17 protons and 17 electrons. By adding one more electron we get a negatively charged Cl- ion with a net charge of -1.
Positively charged Na+ and negatively charged Cl- ions are so un-reactive that we can safely take them into our bodies whenever we salt our food.
What makes an acid or base?
When you put molecules into water, sometimes they break down and release an H+ (hydrogen) ion. At other times, you find the release of an OH- (hydroxide) ion. When a hydrogen (H+) ion is released, the solution becomes acidic. When a hydroxide (OH-) ion is released, the solution becomes basic. Those two special ions determine whether you are looking at an acid or a base.
Acids are proton donors
Acids produce H+ ions in aqueous solutions
Bases are proton acceptors
Bases produce OH- ions in aqueous solutions
Example of acid and base neutralizing each other
Hydrochloric acid added to water containing sodium hydroxide (the base) will neutralize each other.
The protons from the acid join with the hydroxyl groups from the base and the resulting solution has a neutral pH.
pH scale and what does it measure?
Ranges from 1 (most acidic) to 14 (most basic)
pH of 7 is neutral
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline. Pure water has a pH very close to 7.