MCAT

I got a 31R on my MCAT!!! Looks like creating this tumblr and re-writing my notes from scratch was a smart idea! Wahoo.

Done With The MCAT

I finished the MCAT! I totally (think I) did great but I have to wait a month. I’m not really sure what else to use tumblr for now.

Ideal and Real Gases

I’ve been so busy with studying that I forgot how valuable typing up confusing things can be.

Ideal Gases: By using ideal gases, we are able to study the effects of temperature, pressure, volume, and mol amount of gas. By the simple equation PV=nRT, all variable relationships can be seen. Ideal gases are best used at high temperature and low pressures to decrease any chance of intermolecular attraction

Avagadro’s Law: V1/n1 = V2/n2. Simply put, as the amount of gas increases in an expandable container, the volume will increase. An example would be blowing up a balloon.

Charles Law:  V1/T1 = V2/T2. As the temperature of a gas increases, so does the volume.

Boyle’s Law: P1*V1 = P2*V2. Pressure and volume are inversely related (in a non-linear way. As one increases, the other decreases.

Real Gases: Here comes the semi-confusing part. At low temperatures and high pressures, the size of the gas molecules becomes noticeable. The real volume will always be higher. Videal = [Vreal - (nb)] where b is a constant that is always positive. If you solve for Vreal, you can see that Videal + nb is a larger number than the ideal volume. Pressure is slightly (but not by much) more complicated. When the molecules are attracted to each other through forces like dipole-dipole interactions, hydrogen bonding, or ionic attractions, the pressure will decrease. This means that Preal<Pideal. When they repel, there will be a great pressure against the walls of the container Preal>Pideal. This part of the equation is Pobs = Preal + (n^2/V^2)(a). Solving for Preal, well see that it is equal to Preal = Pideal - (n^2/V^2)(a). If the molecules are attracted to each other, “a” is a positive number and Preal is less than Pideal. If the molecules are repelled by one another, “a” is a negative number, and Pdeal will be added to the (a) value creating a higher Preal.

It’s much more simple to remember that when molecules are attracted, they come together and there will be less pressure. (a = +) When they repel, there is a large pressure against the walls of the container (b = - ).  For volume, the real volume is always greater than the ideal volume.

Combining the equations, we get [Preal + (a)(n^2/V^2)][Videal - nb] = nRT

Male and Female Anatomy

Males: The gonads in males are the testes. Inside the testes, sperm is made in the seminiferous tubules. These convoluted tubules are associated with two really important types of cells - Leydig and Sertoli cells. Leydig cells are stimulated by leutinizing hormone (LH) and convert cholesterol into testosterone. Testosterone is required for male secondary sex characteristics like pubic hair, lowered voice, growth of the larynx, and fusion of the epiphyseal plate (growth plate). Testosterone also acts on adjacent cells called Sertoli cells. Testosterone acts to encourage sperm production. In the Sertoli cells, testosterone is converted to dihydrotestosterone. Secondly, Sertoli cells are induced by Follicle Stimulating Hormone (FSH) which is required for sperm production. Negative feedback is used by both Leydig cells and Sertoli cells. If too much testosterone is produced, it can act to inhibit GnRH production by the hypothalamus as well as LH production in the anterior pituitary. Similarly, Sertoli cells can inhibit FSH production of the Anterior Pituitary by releasing a peptide hormone called “Inhibin.”

Females: The gonads in females are the ovaries. By birth, all of the ova that a female will produce are made. During puberty, these ova will be released into the fallopian tubes (ovaducts) and try to get fertilized. In order for all this to happen, lets back up a little. A primary oocyte is surrounded by granulosa cells which together are called a primary follicle.  Thecal  cells now surround this primary follicle and create what is called a secondary follicle. Theca and granulosa cells are similar to Leydig and Sertoli cells in men. Theca cells are stimulated by LH and make testosterone from cholesterol. The testosterone is then converted to estrodiol (a form of estrogen) in Granulosa cells. Similar to Sertoli cells, Granulosa cells are stimulated by FSH which help mature primary oocytes.

The female menstrual cycle can be broken down into an average of 28 days. During the first 14 days, the primary oocyte has matured to a secondary oocyte. On the 14th day, there is a surge of estrogen which causes a subsequent surge of LH. This LH surge (known as the luteal surge) causes the secondary follicle to burst, releasing the secondary oocyte into the ovaduct.The left over follicle is now called the Corpus Luteum and begins to secrete both estrogen and progesterone. In combination, these two steroid hormones inhibit LH secretion from the anterior pituitary. This allows for the endometrium to grow and thicken. This occurs for 2 weeks after ovulation. If fertilization does not occur, the endometrium will be shed and the Corpus Luteum will degrade into the Corpus Albicans.

The period of 14 days up till ovulation is known as the Follicular Phase. The period from ovulation until degredation of the Corpus Luteum is known as the Luteal Phase. The shedding of the uterine lining is known as “flow.” Flow represents the last 5 days of the cycle and is observed by vaginal bleeding.

Acids and Bases

Time for some chemistry!

Acids and Bases can be classified by 3 different defintions

1. Arrhenius Acids and Bases: An Arrhenius acid in water will increase the [H+] concentration. An Arrhenius base will increase the hydroxide [OH-] concentration.

2. Bronsted/Lowry: An acid will donate a proton while a base will accept a proton.

3. Lewis Acids/Bases: A Lewis acid (electrophile) will accept an electron while a Lewis Base (neutrophile) will donate an electron. Usually, a Lewis acid has a positive charge or an empty orbial (such as BF3). Transition metals like Fe3+ are also Lewis acids because of their positive charge. Lewis bases want to become neutral so they have negative charges due to carrying extra electrons.

A compound can be classified as a strong acid or base if it dissociates 100% in water

Strong Acids: HNO3, HCl, HBr, HI, H2SO4, HCLO4, HCLO3

Strong Bases: LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

Water is unique in that it is amphoteric. It can act as either an acid or a base

The strength of an acid or base is defined in 2 ways. Its pH/pOH, and its pKa/pKb.

pH = -log[H+],  pOH = -log[OH-]. pH is on a scale from 0-14 with 0 being extremely acidic and 14 being extremely basic. Depending on the concenrations, numbers can be below 0 (negative) or above 14.

Pure H20 will ionize completely. H20 -> H+ + OH-

Writing out the Keq equation, Keq = Kw = [H+][OH-] = 10^-14, meaning H and OH have values of 10^-7. THIS IS ONLY VALID AT 25 degrees C. If the temperature is raised, there is a large amount of H+ and OH-. Looking at equilibrium stresses, a shift to the products side means that the reaction is endothermic.

For example, if the new Kw = 10^-12, H+ and OH- are equal to 10^-6 (which is a much higher concentration than 10^-7. The -log(10^-6) = pH = 6. The new neutral pH at that higher temperature is equal to 6.