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An acid ionization constant, Ka, also known as acid dissociation constant is a quantitative measure of the acidity of a specified solution. It is the value of a chemical reaction quotient at equilibrium for a dissociation chemical reaction in the context of acid-base reactions. The common dissociation equation of an acid when its at equilibrium is represented as  “HA (aq) + H2O ?? A? (aq) + H3O ? (aq)”. And the reaction is considered to be at equilibrium when the concentration of the generic acid “HA”, the conjugate base of the acid “A-” and the hydronium ion “H+” quit on changing during time. Ka is characterized by: K= A? H3O? / H2O HA noting that the concentration of water will remain constant at equilibrium in a dilute solution. And since the concentration of water is constant, it is allowed  to be a part of a new equilibrium constant  known as the dissociation constant, Ka :  Ka= K H2O = A? H3O? / HA.For practical reasons, it is more convenient to use the logarithmic constant, pKa. It is commonly used as it facilitate mathematical calculations and turns large numbers into smaller and more suitable ones. pKA could be calculated by taking the negative log of a given acid dissociation constant Ka “pKa= -log Ka”. It presents how strong or weak an acid is. The higher the pKa the weaker the acid and the lower the pKa the more stable the conjugate base is. This experiment will determine the acid dissociation constant of Ascorbic acid which is a very known organic acid for its antioxidant properties. The determination of the acid dissociation constant is found by figuring out the pH of a solution obtained by mixing special water with the ascorbic acid and then using it to find the concentration and the Ka of the organic acid solution. Reaction: C6H8O6 + H2O ?? C6H7O6? + H3O?Materials and Chemicals: – Safety goggles- Lab coat- One Digital scale- One scoop- Two Beakers- pH meters- 0.01 moles of ascorbic acid- 100 ml of special water which is a green mixture of BTB, tap water, and deionized waterMethod:Start by wearing both the lab coat and the safety goggles. Using the formula “m=n/M”. Convert 0.01 moles of ascorbic acid to grams. On the digital scale, place one beaker and start scooping out 100 ml of the organic acid. When the required amount of the ascorbic acid is taken out, move it to the second beaker containing 100 ml of the special water obtained by mixing specific amounts of BTB, tap water and  deionized water. Now mix properly. Finally,  find the pH of the obtained solution using the pH meter. Results: pH of solution = 2.61 C6H8O6C6H7O6?H3O?Initial Concentration0.100Change in concentration-x (or 2.45 x 10^-3)+x   (or + 2.45 x 10^-3)+x    (or + 2.45 x 10^-3 )Equilibrium(0.1 – x)  or  0.09755X ( or 2.45 x 10^-3 )X (or 2.45 x 10^-3 )C = n / v =  concentration = number of moles / volume =  0.01 mol / 0.1 dm^3 = 0.1 M     The pH formula:     pH = -log H3O?                          H3O? = 10^(-PH) = 10^(-2.61) = 2.45 x 10^-3 Ka = C6H7O6? H3O? / C6H8O6                Ka = (x)(x) / (0.1 – x)ka=  (2.45 x 10^-3 )( 2.45 x 10^-3 ) / 0.09755 = 6.153 x 10^-5 Pka = -log (ka) = 4.2 Ka pKaAscorbic Acid C6H8O66.153 x 10^-5 4.2 Citric Acid C6H8O77.244 x 10^-4 3.14 Discussion:As shown in the data, the acid dissociation constant (Ka) of the ascorbic acid was calculated to be 6.153 x 10^-5, resulting in a pKa value of 4.2 (pKa= -logKa). Concerning citric acid, the Ka and pKa values were obtained from trusted sources where Ka= 7.244 x 10^-4 and pKa= 3.14. Comparing these values, we see that the Ka value for ascorbic acid is less than that of the citric acid. In addition, the pKa value for citric acid is less than that of the ascorbic acid. The strength of an acid refers to the extent that it dissociates into ions when dissolved in water. When acids react with water, they produce hydrogen ions or hydronium ions. Since Ka is a measure of the strength of an acid,  the larger this number gets the larger tendency the reaction has to drive towards the products side and the stronger tendency the acid has to donate its H+, resulting in a stronger acid. Additionally, and since the pKa value is calculated by taking the negative logarithm of the Ka value, the smaller the pKa value is the more acidic a substance is, i.e stronger acid. All these information signifies that the citric acid is stronger than the ascorbic acid.             Sources of errors and improvements: Some experiments may be error-free, but mistakes do happen often in labs. Concerning this experiment, the accuracy of the results could have been affected by some factors or lack of proper materials. For example, if a 4 digits scale was used when measuring the weight of the organic acid instead of a 2 digits scale, the results could have been more precise during calculations. Additionally, the accuracy of the pH meter was questionable and agreed to be not very precise as the numbers were moving up and down all the time. Overall, the experiment was successful seeing that intelligible results were acquired.

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