muddiest points of student concerns (numbers mean that more than one person asked it)
1. 2 people: buffers –buffers are chemicals which reduce the change of the pH of
water (or any solvent). When you add acid to water, the pH lowers rapidly
depending on how much acid you add. If the water has a buffer, the buffer
absorbs some of the H+ ions, which reduces the change in pH. Buffers absorb H+
ions when the pH is less than 7 and release H+ ions when the pH is greater than 7.
2. 2 people: chemical bonds –are bonds between atoms when two atoms share,
donate or accept electrons. There are three types of chemical bonds: ionic bonds,
covalent bonds, and H-bonds (or hydrogen bonds). Ionic bonds are when one
atom donates an electron or electrons to another atom which accepts it (them). A
covalent bond is when two atoms share electrons. When talking about covalent
bonds, a single bond is made up of a pair of electrons which are shared by both
atoms. H-bonds are when two or more molecules are polar and hydrogen has a
partial positive charge and another atom has a partial negative charge. This
allows the partial negative and partial positive (hydrogen) atoms of two different
molecules to be attracted together, creating the hydrogen bond.
3. H-bonds and the polarity of water –H-bonds are hydrogen bonds that form
between two different molecules when each molecule is polar (has covalent bonds
an atom and with an atom of hydrogen where the electrons are not shared
equally). As the electrons are not shared equally, they spend more time with the
other atom (usually, O, N, or P or S in biological molecules) than they do with
hydrogen, making the hydrogen atom partially positively charged and the other
atom partially negatively charged. A molecule with a partially charged atom (or
atoms) is called polar (though sometimes one having a complete charge or more is
also called polar, strictly speaking this should be called ionic, but since ionic
molecules are often also polar, people just call them polar because we tend to be
lazy.) As the molecule is polar (having a partially negative atom and a partially
positive hydrogen atom), it will have an electrical attraction with another polar
molecule. The partially positive hydrogen in the first molecule will be attracted to
a partially negatively charged atom in the other molecule, and this is called a
hydrogen bond. Two water molecules will show this and this is why water is
polar.
4. 2 people: capillary action –do not worry about this one, because water forms
hydrogen bonds, it tends to stick to other substances (glass for example) that also
have hydrogen bonds. This can create capillary action, where the water is pulled
up.
5. textbook pH formulas –do not worry about something like this:
pH = pKa + log([A-]/[HA])
Just understand that the pH is a measure of the number of H+ ions in solution,
that with acidic solutions the pH is lower (pH < 7) and basic solutions the pH is
higher (pH > 7). I may however ask you something like if the pH is 7, how many
H+ ions are in solution (1 H+ ion in 1 x 107 water molecules). This is pretty
simple, because what the pH is is also what the exponent is (for example, if the
pH = 3, there is 1 H+ ion in 1 x 103 water molecules).
6. 4 people: prokaryotes vs eukaryotes –all living life forms can be divided into two
categories (superkingdoms) based on whether they have a nucleus or not.
Eukaryotes have a nucleus, prokaryotes do not (eukaryotes also have organelles,
prokaryotes do not).
7. kingdoms/domains –if we break all living life forms in eukaryotes and
prokaryotes, we can break eukaryotes and prokaryotes into domains. Eukaryotes
have no division, meaning Eukaryotes is both the superkingdom and the domain,
prokaryotes are broken into eubacteria and archea (archeabacteria). We can then
divide each domain into kingdoms. Eubacteria and archea have no kingdom
divisions, meaning their kingdom is the same as their domain. Eukaryotes are
broken into the kingdoms animals, plants, fungi, and protists.
8. 2 people: archae and eubacteria and eukaryotes, and relationships to kingdoms.
See the two above answers and put them together.
9. finding the atomic mass, neutrons, and protons for an unknown element & vc vs.
I will only ask you to do this if I give you a table of the elements, or more likely,
the info for one of the elements in the table. Each element has an atomic number
in the table (which is the number of protons) and the atomic mass (which is the
average weight of all atoms, each atoms weight is the protons plus the number of
neutrons in the atom (meaning each proton and neutron have a mass of one).
Now getting the number neutrons is a little trickier; it is the atomic mass minus
the atomic number and then round to the nearest whole number (as the mass is not
a whole number but the number of neutrons is).
10. the chemical equations and how you determine their outcomes, the math?
I am afraid I do not know what you are asking.
11. chemistry in general –this one I cannot explain simply. If you are having trouble
with chemistry in general, then I suggest you see me during office hours and that
you read the chapter on chemistry twice.