pH question

[wait4me]

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"If the patient took an antacid that neutralized 99.9% of HCl, what would the pH of the resulting solution be? the pH of gastric juice is 1" The answer to the problem is pH 4. I dont understand how they got this number.

On the same passage, I dont understand how to answer this question:

"The pH of a solution produced when 10mL of gastric juice and 10mL of pure water combine is about:"

 

[loveoforganic]

pH = 1 means [H+] = 0.1 M. (0.1 M HCl)*(0.001) = 0.0001 M. -log0.0001 = 4




pH = -log[H+], so [H+] = 10^-pH. [H+] = 10^-1 = 0.1 moles / liter

(0.1 moles / liter)*(0.01 liters) / (0.02 liters) = 0.05 moles / liter = 0.05 M

-log5*10^-2 = pH = 2-log5 = something around 1.3