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Matt C.
Personalized High School Chemistry and Biology Tutor
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Organic Chemistry
TutorMe
Question:

You are hired by a diaper company to make a new, spill-proof diaper. Keeping in mind molecular polarity, what type of material should you make your diaper with? Assume that feces and urine are made almost entirely of water.

Matt C.
Answer:

The first consideration in designing this diaper is: "what type of material would best adsorb (or stick to the surface, not to be confused with aBsorb) to the diaper without leaking through or around?" For this, we need to remember that "like attracts like"; polar compounds will adsorb better to other polar compounds due to the intermolecular forces between them. The second consideration is to determine the polarity of water: if we know the polarity of the material that we need to catch, we can then make the diaper with material of the same polarity. By comparing the electronegativity of water's component atoms (oxygen and hydrogen), and by taking into account the lone pair of electrons on oxygen, we know that oxygen has a partial negative charge and each hydrogen has a partial positive charge. Thus, water is a polar compound. Since our diaper material must match the polarity of water, our diaper must be made of a polar compound.

Basic Chemistry
TutorMe
Question:

What is the Bohr-Rutherford model of the atom? How does it differ to the modern structure of an atom?

Matt C.
Answer:

The Bohr-Rutherford model of the atom suggests that the nucleus of an atom contains a positive charge and is surrounded by negatively charged electrons. These electrons are said to be circling the nucleus in "orbits", similar to how planets orbit the sun. Each orbit is said to contain a maximum of eight electrons, have a specifically quantified energy level, and be able to give the exact position of an electron around a nucleus. This was a vast improvement compared to previous atomic models, but is not the most accurate model to date. Nowadays, it is recognized that electrons don't float around the nucleus in defined orbits, but rather "orbitals". Orbitals have various shapes them: not all orbitals make electrons circle around the nucleus like planets around the sun. Instead, each orbital - called "s", "p", "d", or "f" depending on their shape and atomic properties - has a defined set of shapes and phases. For example, a "p" orbital is often compared to a dumbbell; an electron moves around the nucleus in a figure-eight-like manner. Unlike the Bohr-Rutherford model, each orbital can only hold up to two electrons. However, there are multiple orbitals within the same energy level (a maximum of 7 orbitals depending on the size of the atom), and can thus hold more than eight electrons in a single energy level. Finally, an orbital doesn't describe an electron's exact position like an orbit does, but rather the probability that an electron will appear within a defined orbital.

Biology
TutorMe
Question:

What is the purpose of the bicarbonate (HCO3-) buffer system in blood? How is HCO3- formed and how is it ultimately removed from the body?

Matt C.
Answer:

There are two main purposes for the bicarbonate buffer system: one is to maintain a homeostatic pH level of 7.4, while the other is to remove carbon dioxide (CO2) - a byproduct of cellular respiration - from cells. CO2 is formed from several different steps throughout cellular respiration and should not accumulate in cells. Carbonic anhydrase uses water to catalyze the hydration of CO2 into carbonic acid (H2CO3), which rapidly dissociates into bicarbonate (HCO3-) and a proton (H+). HCO3- can now be transported out of the cell and into the blood. Once in the blood, the weakly basic HCO3- can neutralize excess acid in the blood by accepting a proton and producing the weakly acidic H2CO3. H2CO3 can then protonate and neutralize excess bases found in the blood to re-produce HCO3-. This equilibrium between HCO3- and H2CO3 shifts based on the amount of excess acid or base in the blood, creating pH homeostasis in the blood. Excess HCO3- in the blood is transported to the lungs via red blood cells. Once in the lungs, it is readily protonated to form H2CO3, where carbonic anhydrase readily dehydrates it into CO2 and water. The CO2 is then exhaled from the lungs, ultimately removing it from the body.

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