Answer
1.1
Work Step by Step
p[H] = -log[H]
[H] is the molar concentration hydrogen ions
[H] = moles of NaOH used to neutralize the gastric juice
7.2 ml of 0.1M NaOH solution contains = (7.2 $\div$ 1000) L $\times$ 0.1 moles/L = 0.00072 moles
10 mL of gastric juice neutralized by 0.00072 moles
So 10 mL of gastric juice contains 0.00072 moles of Hhydrogen ions
So 1 liter of gastric juice will contain 100 $\times$ 0.00072 moles = 0.072 moles
[H] = 0.072 M
pH = -log[0.072] = 1.1
