BIOL-WRITTEN

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BIO 1121 Unit 2 Written Assignment Question 1 The pH of a solution describes its acidity or alkalinity: Describe how pH and H 3 O + concentration is related and explain why diluting an acid raises the pH, but diluting a base lowers the ph. The concentrations of H+ ions in the solutions are represented by PH (OpenStax College, pg. 52). The H+ ion is a relatively small and positive particle with a high charge density, which is why it identified a molecule to bind to. It generally binds to a water molecule. H2O+H+H3O+. In other words, H+ ions occur in H2O solutions as hydronium ions (H3O+). As a result, their concentrations are equal, and pH equals the unfavorable logarithm of H+ concentration. pH=- lg[H+]. It signifies that the pH is 1 if the concentration is 0.1M or 10-1M. The pH is 2 if the concentration is 0.01M or 10-2M. A higher pH indicates a lower acid content. pH is 6 when an acidic solution is diluted to 10-6M. 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? Donor acid – PHO4 – is hydrogen ion. Acceptor: hydrogen ion (H2PO4) Take the following and combine them: • 14.4g Na2HPO4 (dibasic anhydrous) • 2.4g KH2PO4 • 80g NaCl • 2g KCl (monobasic anhydrous) • distilled water (800 mL) 1. Using HCl, raise the pH to 7.4. 2. Fill 1L with H2O, 3
3. Autoclave for 20 minutes on the liquid cycle after adding H2O to 1L. Place in a cool, dry place. 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) 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? Once they've been dissolved in water, they're ready to use. NaCL forms Na+ and Cl-ions. KCL will generate the ions K+ and CL. 2Na+ and HPO4- ions will be formed by Na2HPO4. K+ and H2PO4- ions will be formed by KH2PO4. 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. When the concentrations of solutions are as described as ‘molar’, this refers to number of moles per litre eg a 3-molar solution of NaCl will contain 3 moles of NaCl in 1 litre of water. As indicated above, the M.W. of NaCl is 58.44g, so in 58.44g there are 6.02 x 10 23 NaCl molecules ie 1 mole. So, for 3 moles of NaCl you would need to dissolve 175.32g in 1 litre of water (175.32/58.44 =3) whereas If you only dissolved 29.22g of NaCl in 1 litre of water this would result in a 0.5 molar solution (29.22/58.44= 0.5) 1. As directed you need to check the periodic table and pick up the atomic masses for each of the component atoms in the compounds. For example, for NaCl you need to pick the atomic weight of both sodium and chlorine and then add them to two decimal places to obtain the molecular mass of NaCl. Be sure to multiply the atomic masses by the number of individual atoms of the same element present in each compound before finally adding to the masses of other component atoms of other elements to make up the total molecular masses. 2. From there you can calculate the number of 'moles' of each compound by multiplying the provided weight of compound used in the PBS solution by their respective molar mass conversion factors (i.e. 1L divided by the molecular mass you have calculated in the first step) 3. Now, the molarity in Mol per Litre (mol/l) is given by the 'number of moles' of each compound (calculated in step 2 above) divided by the given volume of the solution. For more information on how to calculate morality, refer to wikiHow's 4 Ways to Calculate Molarity . Using periodic table found in your textbook, calculate (to 2 decimal places) the molecular mass for each of the compounds used to make PBS.
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Create the following table and fill it in with the mass of each component required to make 1 litre of 10 x PBS (the recipe for 10x PBS is below question 2) and their final molar concentration in the buffer calculated as described above. Compound formula Molecular mass (in g/mol) Mass of compound per litre of 10x PBS (in g) Molar concentration (in mol/l) NaCl 55.44 8.0 1.37 KCl 74.55 0.2 2.7 Na 2 HPO 4 141.96 1.44 9.86 KH 2 PO 4 136.09 0.24 1.8 Question 5 As previously stated, the concentration of NaCl, KCl and Phosphate in working strength 1 x PBS is 0.137M NaCl, 0.012M Phosphate, 0.0027M KCl, pH 7.4 How do they compare to the concentrations you calculated for 10x PBS? Watch the following videos and answer the remaining questions " Using an Electronic Balance " from Bio-Rad tutorials “ Using a pH Meter " from Bio-Rad tutorials " Making a PBS solution " from Community College Consortium for Bioscience Credentials In comparison to 1 x PBS, the concentration of 10 x PBS 1 was calculated to be 10 times higher. Question 6 What is the first thing to do after putting a weighing boat on the balance? The balance must be reset to zero. We don't need to keep track of the weight of the boat. Question 7 If you have excess reagent on the weighing boat, what should you avoid doing and why? Not to return and pollute the bottle, but to eradicate it.
Question 8 If you had the choice between a 1-litre beaker and a 1 litre graduated cylinder, which one should you use to measure volumes with maximal precision when making 1 litre of PBS? (you can perform an internet search to find this if you are not sure of the answer) Because it is accurate, I would prefer a 1-liter graduated cylinder. The graduation of the beaker is also approximate. Question 9 What should be done before measuring an unknown pH of a solution using a pH meter? To begin, concentrate the pH meter. For calibration, three separate standard buffers are used: acid, neutral, and basic. PBS is made by dissolving substances in 800ml H2O, adjusting the pH to 7.4, and then adding H2O up to 1 liter. Because the pH of a solution remains stable once diluted if the concentration of its constitutive avid and base isn't too low, the final pH should be 7.4. Question 10 The recipe for PBS says to dissolve compounds in 800 ml of water, adjust the pH to 7.4, then add water up to 1 litre. The final pH should still be 7.4, because the pH of buffer solutions remains stable when they are diluted as long as the concentration of its constitutive acid and base is not too low. Why do you think the protocol does not say to dissolve compounds directly in 1 litre of water? I don't believe it's for the purpose of destroying the pH, but rather for some other chemically concentrated reaction. Question 11 The PBS protocol above says to adjust pH to 7.4 with HCl. What does this imply on the pH of 10x PBS before adjusting the pH, would it be greater or smaller than 7.4? The pH level will be higher than 7.4. Because HCl is an acid, adding it to a solution lowers the pH. Question 12 The last step in the protocol is to autoclave the 10x PBS solution. Why do you think this step is important? Look up the definition of autoclave if you are unsure what it means. The PBS solution is sterilized in an autoclave to avoid contamination when it comes into contact. Question 13 Taking into account your response to question 5, now that you have made a 10x PBS solution, describe how you would prepare 1 litre of 1x working solution PBS, including which glassware you would use. Will you need to adjust the pH again?
The first thing I'd do is pour 800 gallons of water into a graduated cylinder, then pour into the water: KCl 0.2 NaCl 8.0 KH2PO4 0.24 Na2HPO4 1.44 Using HCL, adjust the PH to 7.4 To make 1 liter, add H2O. On the liquid cycle, autoclave for 20 minutes. Keep the container at room temperature. There are 1555 words in this article. References: OpenStax College (2013) Biology. OpenStax College Clark, M.A., Choi, J. & Douglas, M. (2020, Jan 18). Biology 2e. Open Stax . Available online https://openstax.org/books/biology-2e/pages/preface or for PDF download at the following links:
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