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Strong and Weak Acids And Bases

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Introduction

Strong and Weak Acids and Bases Khan Salinder Purpose In this lab, a comparison will be made of the properties of strong and weak acids, as well as properties of dilutions of strong acids. Results & Analysis Experiment #1- Measurement of pH Values Calculations for Theoretical Values of pH Hydrochloric Acid 0.1M HCL HCl --> H+ + Cl- 0.1M HCl = 0.1M [H+] pH= -log[H+] pH= 1.0 0.01M HCl HCl --> H+ + Cl- 0.01M HCl = 0.01M [H+] pH= -log[H+] pH= 2.0 Ethanoic Acid 0.1M CH3COOH CH3COOH ? H+ + CH3COO- Ka =1.8x10-5 Ka = [H+][CH3COO] / CH3COOH] [ ] CH3COOH --> H+ + CH3COO- I C E 1.8x10-5 = [x][x] / [0.1] x2= 0.0000018 x = 0.0013 = [H+] pH= -log0.0013 pH= 2.9 0.01M CH3COOH CH3COOH ? H+ + CH3COO- Ka =1.8x10-5 Ka = [H+][CH3COO] / CH3COOH] [ ] CH3COOH --> H+ + CH3COO- I C E 1.8x10-5 = [x][x] / [0.01] x2= 0.00000017 x = 0.00041 = [H+] pH= -log0.00041 pH= 3.4 Sodium Hydroxide 0.1M NaOH NaOH --> Na+ + OH- 0.1M NaOH = 0.1M [OH-] pOH= -log[OH-] pOH=1 pH=14-1=13 pH= 13.0 0.01M NaOH NaOH --> Na+ + OH- 0.01M NaOH = 0.01M [OH-] pOH= -log[OH-] pOH=2 pH=14-2=12 pH= 12.0 0.001M NaOH NaOH --> Na+ + OH- 0.001M NaOH = 0.001M [OH-] pOH= -log[OH-] pOH=3 pH=14-3=11 pH= 11.0 Table 1- Experimental ph Values pH Value from pH paper � 0.5 Observation of ph Paper pH Value from pH meter � 0.05 0.1 M hydrochloric acid 1.0 Dark Red 1.10 0.01 M hydrochloric acid 2.0 Red 1.92 0.1 M ethanoic acid 3.0 Brown 2.75 0.01 M ethanoic acid 5.0 Light Orange 4.35 0.1M Sodium Hydroxide 12.0 Dark Green 13.76 0.01M Sodium Hydroxide 10.0 Green 11.63 0.001M ...read more.

Middle

This is exactly what should be expected, because with an increase in concentration of HCl, the concentration of hydrogen ions in the acid also increases. 0.1M Ethanoic acid had a pH of 3, so we can say that it was less acidic than the 0.1M hydrochloric acid. This is because ethanoic acid is a weaker acid while HCl is a strong acid with more hydrogen ions in its solution. The pH of an acid is defined as the 'power of hydrogen', so as the hydrogen ion concentration increases, the pH decreases. We can use this data to determine the exact value of the pH for HCl and ethanoic acid. From our results, we can determine that hydrochloric acid is a strong acid as it had a lower pH value as a dissolved substance, meaning there were many ions dissociated in the solution, resulting in more hydrogen ions. Ethanoic acid had a higher pH value, meaning there were less ions in the solution, less ions disassociated, fewer hydrogen ions, and therefore is a weaker acid. Our experimental and theoretical values were off, but these differences can be determined by human errors. The total % uncertainty for the pH paper was much greater than the total % error. Because the % uncertainty was larger than the % error, equipment uncertainties were more significant than systematic errors, while using the ph paper. Because the % error was larger than % uncertainty for ph meter, systematic errors were more significant than equipment errors. These % values make sense as the pH meter is obviously much more accurate than the pH paper. There were a few possible errors for this experiment. The errors of the pH paper were much more significant than human errors. ...read more.

Conclusion

Taking readings at eye level to avoid parallax errors would also improve measurement errors. Other human errors could have been adding too much of too little of a solution, which would effect the reactions. Conclusion In this lab we learned that: The properties of weak bases are: * Low conductivity * Less basic (lower pH values than strong bases) Weak bases will dissociate less, and therefore will have fewer ions to conduct heat/electricity. They will be less basic because there won't be as many OH- ions in the solution and pOH values will be high, resulting in low pH values. The properties of strong bases are: * Very high conductivity * Very basic (high pH values than weak bases) Strong bases will dissociate more, so there will be more OH- ions for conductivity, and to decrease the pOH values, which in turn will increase the pH values. This will make the solution very basic. The properties of weak acids are: * Low conductivity * Less acidic (higher pH values than strong acids) As with weak bases, weak acids will ionize less, so there will be fewer hydrogen ions for conductivity, and this will increase the pH values, making the solution less acidic. The properties of strong acids are: o High conductivity o Very acidic (low pH values than weak acids) Strong acids will ionize more, so the increase in hydrogen ions will improve conductivity and lower the pH value, making the solution more acidic. The properties of dilutions of strong acids are: o The more dilute solutions of strong acids will be weaker conductors and will have higher pH values. T o There will be fewer molecules to ionize, resulting in fewer hydrogen ions. As mentioned above, fewer hydrogen ions will result in the solution being a weaker conductor, and in being less acidic (higher pH value) ...read more.

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