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2800graph - [HA ratio became the smaller the change in pH...

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Brittney Brown October 20, 2010 Chem 2800/L Partner: Erica Francis For both Figures 1 and 2, the more diluted the acid became the more basic the pH changed. The acid reacted with the water causing the concentration of the OH - ion to increase resulting in an increase in the pH. The more the acid was dilution, the more basic the solution became. HCl is a strong acid and completely dissociate in water. At the end of the dilution series, HCl had a higher pH than acetic acid. In Figure 3 and 4, the concentrations of the buffer system stayed the same. Even as the concentration stayed the same, the pH increased for the acidic buffer solution and decreased for basic buffer solution. Even thought the concentration is constant the ratio of [A - ]/[HA] is different and resulted in a change in pH prevalent to their relative amounts. In Figure 5, as the [A - ]/[HA] ratio decreased, the ΔpH also decreased except for the dilution series G and H. The ΔpH started to go back up for the dilution series G and H. The closer to 1 the [A
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Unformatted text preview: -]/[HA] ratio became the smaller the change in pH became. Table 1. The Buffer Region Solutions Spiked with HCl 0.1M Acetic Acid (mL) 0.1M Sodium Acetate (mL) pH 0.1M HCl (mL) pH ΔpH 1 24 3.74 2 3.03 0.71 3 22 3.86 2 3.35 0.51 5 20 4.12 2 3.76 0.36 10 15 4.63 2 4.40 0.23 12.5 12.5 4.60 2 4.56 0.14 15 10 4.92 2 4.73 0.19 20 5 5.26 2 5.06 0.20 24 1 5.97 2 5.44 0.53 Table 2. The Effect of Ionic Strength on pH 1.0M HCl (µL) Ca(NO3)2 (mL) pH measured-log[H + γ]-log[H + ] 250 2.0 2.66 2.69 2.60 250 5.0 2.53 2.69 2.60 250 10.0 2.58 2.71 2.60 250 15.0 2.55 2.72 2.60 250 25.0 2.55 2.73 2.60 250 30.0 2.50 2.73 2.60 The measured pH values were very inconsistent and wrong. The calculated pH values without including the activity of the salt were all the same values. The calculated pH including the activity of the salt was a more accurate measurement of the pH. As the ionic strength increased, the activity coefficient decreased....
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