CHEMISTRY ASSESMENT 1 Essay Example
PART A — 300 words +/- 10% (20 marks)
1) Consider the following reaction at equilibrium
(a) Explain what is meant by a reaction at equilibrium. (2 marks)
Helleur (2012) reaction of oxygen with hemoglobin gives oxyhemoglobin as the product. The reaction is balanced forming an equilibrium reaction termed as dynamic equilibrium. This is so because there has been balanced established in respect to hemoglobin movement exhibiting feasible forward and backward reaction as above.
(b) Which direction will equilibrium shift if the O2 concentration is increased?
Within the lungs there is more oxygen. Increase in oxygen concentration shifts the equilibrium to the right so as to counteract the rising amount of oxygen via increase oxyhemoglobin production.
(c) Which direction will equilibrium shift if the HbO2 concentration is increased?
To the left. Oxygen decreases in concentration within the tissues. The equilibrium is re-established by a shift to the left with more oxyhemoglobin being decomposed to increase oxygen concentration.
(d) In which direction will the equilibrium shift if the Hb concentration is decreased? (1 mark)
When there is a decrease in hemoglobin (Hb) the equilibrium will shift such that Hb increase. Therefore, HbO2 will dissociate, to increase Hb, and the equilibrium will shift to the left.
(e) Name and briefly explain the principle you applied in answering b) — d).
Le Chatelier’s principle: According to Le Chatelier’s principle a disruption of a dynamic equilibrium by altering the conditions, the equilibrium position shifts in a way that it counteracts the current change by re-establishing a new equilibrium. For a chemical reaction, at equilibrium, when a change in reactants or products concentration, temperature or pressure arises, there is a shift in the equilibrium to the opposite direction to counterbalance the change. Therefore, change in an equilibrium system such that there is an increase in the reacting species concentration, the system favors the consumption side of the particular species. That means, increase in products, increases the reaction quotient Qc, rising it more than the constant of equilibrium, Kc.
2) Write the equilibrium constant expression for the reaction shown in question 1.
(2 marks). Helleur, (2012) the law of mass action gives the existing relationship between a balanced chemical equation and the products and reactants concentrations; which is always products divided by reactants, where K is the equilibrium constant, with no unit.
3) Calculate the equilibrium constant using the following concentrations
[Hb] = 2.27 x 10-8 M, [O2] = 9.5 x 10-2 M and [HbO2] = 6.93 x 10-1 M.
Your answer should be presented to two decimal places in exponential notation. (2 marks)
= K= 6.93÷21.565=
Exponential sum: -8+(-2)=-10; -1-(-10)=9
Answer: 0.3213540459 x109 =3.218 (Bettelheim, Brown, Campbell, Farell & Torres, 2012)
4) K values can be small, large or intermediate (close to 1). Explain what these values indicate in terms of the reaction, and reactants and products at equilibrium. (6 marks)
When Kc>>1, the reaction favors products (reaction nearly complete).
When Kc<<1, the reaction favor reactants (reaction hardly proceeds).
When Kc is intermediate, there is a comparable amounts of reactants and products within the system.
5) Explain the necessary requirements for a chemical reaction to take place. (3 marks)
According to collision theory, three factors must be present for a chemical reaction to occur. The reactants should collide. The reactants must be oriented in that they align themselves well to form and break bonds. Finally, the collision should provide sufficient energy to allow activation of the reactants.
PART B — 600 words +/- 10% (30 marks)
The combination of oxygen (O2) with hemoglobin (Hb), is a complex reaction, but for our purposes here, it can be represented by a simplified equation:
Hb (aq) + O2 (g) HbO2 (aq)
Where HbO2 is oxyhemoglobin, the hemoglobin-oxygen complex that transports oxygen to tissues. Consider the above reaction and address the following:
1) Explain the connection between O2, Hb and red blood cells. (2 marks)
Gaseous oxygen, is only usable within the body when transported via the hemoglobin. Hemoglobin is an aqueous substance contained in the red blood cells. When people breathe in oxygen, the gas diffuses to the red blood cells and binds to the HB forming oxyhemoglobin and is then transported through the body cells, where it dissociate as the blood moves further from the heart.
2) Hb transport protein requires a particular metal ion to effectively transport oxygen around the body. Research which ion this is and state if it is a cation or an anion. Discuss the significance of this ion in relation to oxygen transport. (3 marks) Ion: Iron (Fe2+) ion, a cation. Hemoglobin is coined from two words heme and globin. Each hemoglobin subunit is made of a globular protein containing an embedded heme group. With each heme group is an atom of iron. Being positively charged ion (cation), it binds oxygen ions which is usually negatively charged (anion) thus enabling the transport of oxygen to various body cells (Casiday & Frey, 2008).
3) Explain why O2 requires the transport protein Hb and state the percentage of oxygen transported around the body by Hb. (3 marks)
About, 1.5% of oxygen dissolves directly in blood, however, 98.5% is bound to hemoglobin protein and transported to all body parts. Hb comprises of four subunits: two beta and two alpha subunits. Within each subunit is a central heme group containing iron, which reversibly binds oxygen molecule. Therefore, a single heme group binds four molecules of oxygen. The more oxygen molecule bound the brighter the heme group (Pittman, 2011).
4) Explain where in the body the forward reaction and reverse reactions are most likely to occur, making reference to partial pressures of O2 in your explanation. (6 marks)
Binding of Hb and O2, occur mostly in lungs as inhaled oxygen binds to the hemo group (forward reaction), and the blood flows into the heart. In the heart the blood is then pumped to reach other body parts. As it flows from the heart to the periphery, the O2 partial pressure decrease and sequential unloading of the four oxygen molecules begins. Oxyhemoglobin (HbO2), dissociate as more oxygen is released to the body cells, forming Hb and Oxygen (backward reaction) (Pittman, 2011).
5) Carbon dioxide is a metabolic waste product. Explain the three ways in which carbon dioxide is transported around the body. (4 marks)
Casiday & Frey, (2008) carbon dioxide (CO2) can be transported to within the body via:
Bicarbonate ion: about 85% of CO2 is carried inform of bicarbonate buffer system. CO2 diffuses into the RBC. Within the RBC is carbonic anhydrase (CA) which converts the CO2 into unstable carbonic acid (H2CO3) which breakdown immediately into hydrogen (H+) and bicarbonate ions (HCO3-). The fast conversion of CO2 into HCO3- ions gives room for more CO2 absorption into the blood, as it moves down opts concentration gradient.
Binding to hemoglobin: Abut 10% of CO2 is able to attach itself to plasma proteins or directly enter the RBC and attach to hemoglobin. Within the hemoglobin, it form a carbaminohemoglobin molecule; a reversible molecule and is then carried back to the lungs, it dissociate and is expelled.
Directly dissolution into the blood: CO2 being more soluble in blood compared to oxygen. Approximately 5-7% of CO2 dissolves directly to plasma.
6) Write a chemical equation for the major way carbon dioxide is transported around the body and explain why this reaction is important in the human body. (4 marks)
H2O + CO2 H2CO3
H2CO3 H+ + HCO3—
In reference to Bohr Effect increase in CO2 and H+ concentrations promotes O2 release from hemoglobin within the blood. These phenomenon is fundamental in ensuring successful blood-gas exchange mechanism within the body. As oxygen is carried to the periphery organ it is imperative that it remains bound within the hemo group, but be easily detachable as the blood travels via the arteries to the periphery cells and tissues. CO2 and H+ are products of metabolic activities of the body and the concentration of these elements is high in most metabolic active tissue within the body. Large CO2 and H+ trigger O2 release from the blood depending on the demand (Ibsen, n.d).
7) Which way will the equilibrium shift for the reaction in Question 6 if carbon dioxide levels were higher than normal? What would be the consequences of this happening (from a chemical perspective) and how would this affect the health of an individual? (8 marks)
The equilibrium will shift to the right, as more H2CO3 is being formed. Subsequently this will result into both HCO3- and H+ increase. Increase in CO2 with subsequent unbalanced increase ratio in H2CO3 leads to respiratory acidosis and or depression. However, realizing the CO2 elimination curve nature. That is increase in CO2, leads to increase production of H2CO3 and easily dissociation and removal of CO2 in presence of increase oxygen in lungs, then the abnormalities are not that severe (Ibsen, n.d).
Consider the 3 states of matter: solid, liquid and gas. Explain how temperature affects the 3 states of matter and describe the arrangement of particles and attractive forces in each state. (7 marks)
Bettelheim, et al., (2012) increase in temperature, melts down the solid matter to liquid, which if is increased further, the liquid changes to gas. In some gases increase in temperature changes solid direct to gas through a sublimation process. Decrease in temperature or cooling force the gas to condense and form liquid and further cooling forms solid. In solid state, the matter has strong intermolecular force existing among all particles and thus is why solids have a definite volume and shape, and are rigid in nature. Liquids and gases possess. Liquids have temporal intermolecular attraction force encouraging mobility among particles. Liquids have definite volume provided pressure and temperature are constant but adapts the shape of the container. Gases, are more mobile, the intermolecular attraction force is very weak encouraging random movement of particles colliding with one another. That is why gases have no shape or volume.
State the difference between an ionic bond and a covalent bond. (2 marks)
Bettelheim, et al., (2012) ionic bonds occur between a non-metallic and a metallic atoms and there is transfer of an electron(s) while covalent bond, is a chemical bonding achieved by sharing electron(s) between two non-metallic atoms.
Provide the chemical structure and name for an ionic compound and a covalent compound. (4 marks)
Covalent bonding: Ammonium NH4+
Sodium chloride (NaCl)
State the difference between a non-polar covalent and polar covalent bond. (2 marks)
Polar covalent bonds occur where two non-metal atoms differ in their electronegativity level, and thus, no equal sharing of electrons in forming the bonding pair. The bonding occur by displacing the less electronegativity atom to the more electronegativity atom. For a non-polar covalent bond, a pair of non-metal have same level of electronegativity and they form a bond by equally sharing a pair of electron during bonding. No net electrical charge occurring within such molecules. Within a non-polar covalent bond there is even distribution of electrons.
Provide the chemical formula and name for a polar and nonpolar molecule. (4 marks)
Polar molecules: HCl; H-CL, where Cl, electronegativity is 3.0; and H atom has 2.1.
Non-polar molecules H2; H-H with a 2.1 electronegativity
Explain the following intermolecular forces of attraction between molecules: London dispersion, dipole-dipole and hydrogen bonding. (6 marks)
London-dispersion forces- also referred to as Van der Waal’s force occurs from induced dipole, but with weaker interaction moment compared to interaction within dipole-dipole bonding. Therefore, the weightier the molecule the stronger the van der Waal’s interaction force.
Dipole-dipole intermolecular force occur when a polar molecule positive side attracts another polar molecule’s negative side. A dipole molecule has both negative and positive regions.
Hydrogen bonding- compared to all other intermolecular forces, hydrogen bonding are the strongest. Hydrogen bonds, are dipole-dipole forces whose attraction occur between a somewhat positive hydrogen in one molecule and that on another molecule exhibiting slightly negative atom (Chapter 12, n.d.).
Consider the 2 molecules in Question 5. Explain the type of intermolecular forces of attraction that will exist between the nonpolar molecules and polar molecules. (5 marks)
Hydrogen chloride (HCl) is a dipole-dipole interaction. This is so because, the relatively positive polar molecule end region attracts the negative end region of another molecule of HCl. The two dipoles form an attraction unlike full bond because no sharing of electronics occurring between both molecules.
Two HCl molecules with dipole-dipole interaction.
H2- London dispersion forces, compared to hydrogen bonds, Van der Waals forces have weaker bonds, however in some cases London dispersion forces ca be stronger than hydrogen bonding in reference to the number of electron molecules. Normally, electrons are always on motion. When the electron are on one side there is more negativity while the other side is more positivity. Equal distribution results when electrons are on one side. But when the molecule has unequal distribution the molecule has a dipole, and attraction is present to other molecules exhibiting similar unequal distribution.
Bettelheim, F.A., Brown, W.H., Campbell, M.K., Farell, S.O. & Torres, O. (2012). Introduction to General, Organic and Biochemistry 10th Ed. Belmont, CA, United States. Wadsworth Publishing Con Inc.
Casiday, R. & Frey, R. 2008. Hemoglobin and the Heme Group: Metal Complexes in the Blood for Oxygen Transport. Inorganic Synthesis Experiment, St. Louis, Washington.
Chapter 12: Liguids, Solids and Intermolecular Forces. (n.d.). Retrieved 7/21/2017 from, http://www2.sunysuffolk.edu/joshiv/handouts/PDF/Inter_Molecular_Forces_handout.pdf.
Helleur, R. (2012). Chapter 14: Chemical Equilibrium. Chem 1011 Winter.
Pittman, R.N. (2011). Regulation of Tissue Oxygenation. Morgan and Claypool Life Sciences Virginia Commonwealth University, Richmond, Virginia.
Ibsen, L. (n.d.). Fluids, Electrolytes, and Acid-Base Status in Critical Illness. Retrieved 7/21/2017 from, http://pedsccm.org/FILE-CABINET/Practical/Akron_pdfs/8FLUIDS.PDF.
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