Good Example Of Essay On pH=-Log10h+=-Log10ka[ch3coo-].
1. The pH values for different solutions were obtained by different pH measuring devices. Each device has its accuracy, precision and error. The values obtained by any device, even the most modern and precise, are always subject to error. Therefore, the difference in pH readings of the same solution produced by the different devices tested in the assignment are caused by random instrumental errors. By analyzing the results, a hypothesis about systematic error can be set. For instance, the device Fisher XL600 produces significantly lower results for neutral solutions (pH near 7). Presumably, its functioning is unstable in neutral solutions and it requires calibration.
The error is characterized by standard deviation. The lower the deviation is the more precise are the results.
The solutions used for the test are salts of acetic acid and acetic acids of different concentrations. Therefore, the pH of the solutions will be different. Solutions of sodium and potassium salts are characterized by slightly basic reaction (pH > 7). This is observed in consequence of hydrolysis and formation of low concentrations of sodium and potassium hydroxides that increase pH. Ammonium acetate hydrolysis produces the weaker ammonium hydroxide solution, and therefore pH is lower.
The solutions of acetic acid are characterized with acidic pH (pH < 7). Solutions with higher molar concentrations of acids have lower pH since hydrogen concentration is higher. For example, pH of 1 M solution is 2.32, while 0.001 M solution has pH of 3.55.
2. The pH of weak acids solutions is calculated on the basis of dissociations constants:
Therefore, we can calculate the pH of the solutions. The dissociations constants are tabulated, and kaCH3COOH=5.6∙10-10. The solutions of the salts are calculated using the same formula. Since dissociations constants of ammonium hydroxide and acetic acid are equal, pH of the solution is neutral, e.g. pH = 7.
The calculations are presented in Table 1.
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