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Question 3: 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?                                                                  
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 liter.
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 1023 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 1023 water molecules, or 1 mole of Na+ is equal to 6.02 x 1023  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 1023 atoms of oxygen (O) will have a mass of 16g whereas 1 mole or 6.02 x 1023 atoms of sodium (Na) will have a mass of 23g
Although you may sometimes see it written as g/liter, 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 liter 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 1023 NaCl molecules ie 1 mole. So for 3 moles of NaCl you would need to dissolve 175.32g in 1 liter of water (175.32/58.44 =3) whereas If you only dissolved 29.22g of NaCl in 1 liter of water this would result in a 0.5 molar solution (29.22/58.44= 0.5)

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Subject: Biology, Science

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