WRITTEN ASSIGNMENT UNIT 2

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Dec 6, 2023

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www.UoPeople.edu BIO 1121 Unit 2 Written Assignment UNIT 2: Biological Macromolecules Department of Health Sciences University of the People Instructor: Chidioze Udeogu BIOL 1121-01 WRITTEN ASSIGNMENT 2 June 27 th , 2023 Directions Accurately measuring the volume of liquids, weighing chemicals, and adjusting the pH of solutions are routine procedures in a working laboratory environment. This assignment is designed to provide you with an overview of the general skills and knowledge you would need to perform such tasks. Before completing this assignment, you should ensure you have read your textbook – particularly the section entitled pH, Buffers, Acids, and Bases. Answers should be concise and well written. Make sure you correctly explain your thought process and provide all the necessary information.

www.UoPeople.edu Question 1 The pH of a solution describes its acidity or alkalinity: Describe how pH and H 3 O + concentration are related and explain why diluting an acid raises the pH, but diluting a base lowers the pH. Answer: H 2 O + Hydronium is acidic. When an acid or a base is diluted reduces the ions concentration. When an acid is diluted the pH rises to 7 in it’s way to lessen acidic. And when a base is being diluted, the neutrality decreases from 7 as it becomes less basic. Question 2 Phosphate Buffered Saline (PBS) is a commonly used buffer for experiments in biology because its pH and ion concentrations are similar to those in mammalian organisms. It works in a similar fashion to the blood plasma buffer mentioned in the textbook, but using dihydrogen phosphate ions and hydrogen phosphate ions for buffering through the following chemical reaction: H 2 PO 4 - (aq) ⇆ H + (aq) + HPO 4 2- -(aq) The equilibrium arrows depict that the phosphate ion (H2PO4 - ) is dissociating further into two component ions in solution, but at the same time H + and HPO4 2- ions are combining simultaneously to form phosphate in solution. So, at any given point in time, and under the appropriate conditions, there is an equal quantity of dissolved ions and combined ions in solution. There is therefore always a hydrogen ion donor and an acceptor in solution. Based on the equation above, which ion plays the role of hydrogen-ion donor (acid) and which ion plays the role of hydrogen-ion acceptor (base) in PBS? Answer: As chemical reaction using dihydrogen phosphate ions and hydrogen phosphate ions for buffering is H 2 PO 4 (aq) ⇆ H + (aq) + HPO 4 2- (aq) then ions playing the role of hydrogen-ion donor (acid) is H 2 PO 4 and HPO 4 2- as the receptor (base). Question 3 The composition of PBS is 0.137M NaCl, 0.012M Phosphate, 0.0027M KCl, pH 7.4. Below is the protocol to make 1 litre of 10x concentrate PBS. Combine the following: • 80g NaCl • 2g KCl • 14.4g Na 2 HPO 4 (dibasic anhydrous)

www.UoPeople.edu • 2.4g KH 2 PO 4 (monobasic anhydrous) • 800mL distilled H 2 O 1. Adjust pH to 7.4 with HCl 2. Add H 2 O to 1L 3. Autoclave for 20 minutes on liquid cycle. Store at room temperature. Which ions are being produced by this process, assuming that each of the chemical compounds dissociate into their constituent parts once they are dissolved in water? Answer : Assuming that each of the chemical compounds dissociate into their constituent parts once they are dissolved in water; it's evident that by this process hydrogen ions are being produced. NaCL (s) + H2O ⇆ Na ++CL - Question 4 Preparation of the correct buffer is key to any good biological experiment and it is important that you understand how to calculate the mass of each chemical required to make that buffer and what the resulting concentration of those constituents will be in moles per litre. Your text book explains that moles are just a way to express the amount of a substance, such that one mole is equal to 6.02 x 10 23 particles of that substance. These particles can be can be atoms, molecules, ions etc, so 1 mole of water is equal to 6.02 x 10 23 water molecules, or 1 mole of Na + is equal to 6.02 x 10 23 Na + ions. Since different chemicals have different molecular weights (based on the number of protons and neutrons each atom contains) 1 mole or 6.02 x 10 23 atoms of oxygen (O) will have a mass of 16g whereas 1 mole or 6.02 x 10 23 atoms of sodium (Na) will have a mass of 23g If you need more information on moles, please read Encyclopedia Britannica's Moles website . Although you may sometimes see it written as g/litre, the concentration of solutions is more often described in term of molarity since it better defines the chemical properties of a solution because it is proportional to the number of molecules or ions in solution, irrespective of molecular mass of its constituents. However, it is not possible to measure moles on a laboratory balance, so in the first instance chemicals are measured by mass (milligrams, grams, kilograms etc) and the number of moles is calculated using the known molecular mass (often called molecular weight and abbreviated to M.W.) of the chemical. As indicated earlier, the molecular mass of a chemical is based on the number of protons and neutrons that is contained in each atom ( eg NaCl is made up of one molecule of Na, M.W. = 22.99g and one molecule of Cl, M.W. = 35.45g, so the M.W. of NaCl is 58.44g). These values can be found in the periodic table however the molecular mass of chemicals is generally provided by any vendors of the products and so can also be found on various suppliers’ websites.

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