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When a small amount of acid is added to a non-buffe solution, there is a large change in pH. Calculate the pH when 26.9 mL of 0.0044 M HCl is added to 100.0 mL of pure water. Comment and hint in the general feedback.

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When a small amount of acid is added to a non-buffe solution, there is a large change in pH. Calculate the pH when 26.9 mL of 0.0044 M HCl is added to 100.0 mL of pure water. Comment and hint in the general feedback.

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CatrinMaster · Tutor for 5 years

Answer

<p></p><p>the correct answer is <strong>pH= 2.93</strong></p>

Explain

<p></p><p>HCl is a strong acid.That means it separates. <u><strong>completely</strong></u> in the water as follows:</p><p>hcl(aq)→h+(aq)+cl−(aq )</p><p>When dissociation is complete, the amount of H+ produced is equal to the concentration of HCl.Therefore, we multiply the volume of HCl ( 26.9ml ) added by the concentration of HCl ( 0.0044 m ), and then divide it by the volume of water ( 100.0ml ).Note this factor.26.9ml/100ml is the dilution factor:</p><p> [ HCl ] =..26.9ml/100ml x.0.0044 m =.1.18 x 10−3 m</p><p>We know that pH = -log [ H + ], in this case [ H + ] = [ HCl ] ( because HCl is a strong acid ), so we directly calculate the pH value of [ HCl ] as follows:</p><p>pH = -log[H+ ] = -log[HCl ] = -log ( 1.18 x 10−3 M ) =. <strong>2.92</strong></p><p>please note <u>2.92 is a lower ph</u>So when we add strong acids to the water -- there is no buffer solution -- the pH suddenly drops. </p>
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