Answer :
The answer would be 5.1
Volume of KOH, V1 = 17.2mL
Volume of HCI, V2 = 20mL
Molarity of KOH, M1 = 1.72 * 10 ^ - 4 * M
The given titration is between KOH and gastric juice (HCI).
The molarity of HCI can be calculated using the relation,
M1 * V1 =M2 * V2 ---------- (1)
M2 = M1 * V1 / V2
Where,
M1 is the molarity of KOH.
M2 is the molarity of HCI.
V1 is the volume of KOH.
V2 is the volume of HCI.
Substituting the values in equation (1),
M2 = 1.72 * 10^-4 * 17.2 / 20.00
M2 = 1.49 * 10^ -5 g
The pH of gastric juice (HCI) can be calculated using the
equation, pH=-log[H^ + ] -------- (II)
Since, HCI is a strong acid, it dissociates as follows, HCI H+CI
Therefore,
[HCl]=[H^ + ]=[Cl^ - ]= 1.49 * 10 ^ - 5 * M
Substituting this in equation (II),
pH =-log[H^ + ] = - log[1.49 * 10 ^ - 5] = - log(1.49) + 5 * log(10)
The value of pH is calculated as,
pH = - log(4.78) + 5 * log(10) = -0.17314 +5 = 5.1
Hence, pH of gastric juice is 5.1
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