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# ph measurement and buffer solution lab report

Rinse your buret, small funnel, and four 150-mL beakers several times using deionized water. Label this second beaker “HA” and set it aside for now. From the measured pH and concentration of a weak acid solution you can determine the value of $$K_{a}$$ for the acid. Your instructor will demonstrate the proper use of the pH meters. 2010. 2. $$K_{a}$$ of unknown weak acid: ______________ (, How do you know the concentrations of $$\ce{HA}$$ (. Put the magnetic stirrer onto your buret stand so that the buret is directly over the magnetic stirrer. Includes colorimetric results using different acid-base indicators. Because $$[\ce{HA}] = [\ce{A^{-}}]$$, the pH of this buffer solution equals the value of pKa for the unknown acid. Record your measured value on your data sheet and obtain your instructor’s initials confirming your success. Consider your results for the 0.1 M $$\ce{Na2CO3}$$ solution. Rinse this beaker once more with about 5 mL of 0.2 M $$\ce{NaOH}$$. Department of Medical Technology Use the value of the pH at the midpoint of your graph to determine the value of $$K_{a}$$ for your unknown acid. Now we will test the buffer solution you prepared against changes in pH. Donato Using Equations \ref{6} and \ref{7} , we may express Equation \ref{5} as, $K_{a}=\dfrac{[\ce{H3O^{+}}]^{2} }{[\ce{HA}]_{0} - [\ce{H3O^{+}}]} \label{8}$. This new solution will be a buffer solution since it will contain equal amounts of $$\ce{HA}$$ (aq) and $$\ce{A^{-}}$$ (aq). Faculty of Pharmacy As $$[\ce{H3O^{+}}]$$ decreases the equilibrium indicated by Equation \ref{1} will shift to the right and $$[\ce{HIn}]$$ will decrease while $$[\ce{In^{–}}]$$ increases. The pH of Buffer 2 was 5.5 and the ratio of conjugate base to acid was 5.47. You will then combine equal volumes of these two solutions in order to form a new solution. Then use it to collect about 75 mL of the 0.2 M $$\ce{NaOH}$$ solution. To create and study the properties of buffer solutions. If you are being asked to make a buffer at pH 4.00, what is the appropriate ratio of A. These data will be used to plot a titration curve for your unknown acid. Have questions or comments? Is the color obtained when tested with bromcresol green indicator as expected? Fauni Chapter 7 Lab Report Background Research pH is a measure of the potential hydrogen ion concentration of a solution. Explain. Two buffer systems were created. Record the results on your data sheet. DOCX, PDF, TXT or read online from Scribd, *Single column version due to uploading problems. Measure the new pH and record it. Suppose we add base to the solution resulting in a decrease of $$[\ce{H3O^{+}}]$$. Using your large graduated cylinder, measure out 50.0 mL of your unknown acid solution and transfer this to a second 150-mL beaker. Then use it to collect about 75 mL of the 0.2 M $$\ce{NaOH}$$ solution (available in the reagent fume hood). Recall that the pH of a buffer solution is given by the Henderson-Hasselbach approximation: pH = pKa + log[A −] [HA] Because [HA] = [A −], the pH of this buffer solution equals the value of pK a for the unknown acid. Use equations to support your explanation: Why isn’t the measured pH of the deionized water before adding the $$\ce{NaOH}$$ (. Calculations do not need to be shown here. A buffer resistschanges in pH because it contains both an acidic species to neutralize OH- ions and a basic oneto neutralize H+ ions. For this lab you will be doing a “one- You will use these values to calculate $$K_{a}$$. Add 5 drops of the remaining 0.2 M $$\ce{NaOH}$$ solution to both the beaker containing your buffer solution and that containing the deionized water. Now using the remaining solutions in the beakers labeled “HA” and “A- ”, prepare a buffer solution that will maintain the pH assigned to you by your instructor (see background section). Obtain a magnetic stirrer, magnetic stir-bar, and 50-mL buret from the stockroom. When $$[\ce{In^{–}}]$$ becomes significant compared to $$[\ce{HIn}]$$ the color of the solution will begin to change. Is the solution acidic or basic? Obtain a vial containing your unknown solid acid from your instructor and record the letter and number of this unknown acid on your data sheet. Rinse four small 100 or 150-mL beakers several times using deionized water.