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Imran R.
Premed Chemistry & Biology Double Major
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Chemistry
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Question:

The mass of a nucleus of any element is less than the mass of its constituent nucleons; why is that so? A) When nucleons bind to form an element, they release beta particles to form the electrons that orbit the nucleus. B) When nucleons come together to form a nucleus, some of their mass is converted into nuclear binding energy which keeps the nucleus together. C) When nucleons come together to form a nucleus, high energy photons are released in turn, lowering the mass of the nucleus. D) The binding of nucleons to each other is an exothermic reaction which liberates large amount of heat

Imran R.
Answer:

The answer is B. The protons in a nucleus repel one another due to coulombs law ( F = (q1q2/r^2). What keeps a nucleus from falling apart is the nuclear binding energy which is mediated by the strong force (one of the four basic forces of nature). When nucleons (protons/neutrons) come together to form a nucleus, some of their mass is lost and converted into nuclear binding energy which works against the force of repulsion and keeps the nucleons bound to one another. This energy can be calculated by the equation E = mc^2 where m is the difference in mass between the sum of the nucleons and the resulting nucleus.

Basic Chemistry
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Question:

Phosphoric Acid has three ionizable sites with distinct pka values of approximately 2, 7, and 12. Why is it that every successive dissociation of a proton becomes less thermodynamically favored? A) Release of a proton increases H+ concentration and therefore, decrease further unbinding due to Le Chateliers Principle B) Dissociation of consecutive protons destabilizes pi bonding interactions C) Dissociation of successive protons increases the amount of charge on adjacent oxygen which leads to greater electron repulsion D) Dissociation of successive protons increases entropy which decreases delta G.

Imran R.
Answer:

The answer is C. Phosphoric Acid (H3PO4) has three ionizable sites. Every time a proton (H+) dissociates from an oxygen it creates a negative charge on the oxygen from which it was liberated. Successive dissociations are highly unfavored because the oxygens are in close proximity to one another and therefore, more negative charge leads to a greater repulsion between the oxygens. This causes structural strain in the molecule which causes instability. For this reason higher levels of pH are needed to force the hydrogens off their respective oxygen atoms.

Biology
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Question:

Two friends go hiking at high altitudes where the air is thinner than usual. One is a cigarette smoker while the other is not. The cigarette smoker has an easier time breathing at the top. Why is that so? a) Cigarette smokers have a greater number of alveoli and therefore a greater rate of oxygen absorption b) Cigarette smokers have a greater concentration of 1,3-BPG which increases Oxygen binding affinity for hemoglobin c) Cigarette smokers have a greater lung surface area and in turn, can liberate more blood CO2 d) Cigarette smokers have a greater concentration of 1,3-BPG which increases the amount of oxygen unloaded by hemoglobin.

Imran R.
Answer:

The answer is D. Hemoglobin exists in two forms; the relaxed form (oxygenated hemoglobin) and the tense form (deoxygenated). 1,3-bisphosphosglyceric acid undergoes isomerization to 2,3-BPG in red blood cells by way of an enzyme called BPG Mutase. 2,3-BPG binds to hemoglobin and stabilizes the tense state (deoxygenated), it therefore increases the degree of oxygen release from erythrocites (red blood cells) from roughly 8% to 66%. This causes a much greater delivery of oxygen to respiring cells. So even though the oxygen loading efficiency in smokers is decreased, oxygen delivery to cells is still increased because of higher rate of unloading.

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