In a hospital laboratory, a 10.0 mL sample of gastric juice (predominantly HCl), obtained several hours after a meal, was titrated with 0.1 M NaOH to neutrality; 7.2 mL of NaOH was required. The patient’s stomach contained no ingested food or drink, thus assume that no buffers were present. What was the pH of the gastric juice?

Respuesta :

Answer: 1.14

Explanation:

[tex]HCl+NaOH\rightarrow NaCl+H_2O[/tex]

To calculate the molarity of acid, we use the equation given by neutralization reaction:

[tex]n_1M_1V_1=n_2M_2V_2[/tex]

where,

[tex]n_1,M_1\text{ and }V_1[/tex] are the n-factor, molarity and volume of acid which is [tex]HCl[/tex]

are the n-factor, molarity and volume of base which is NaOH.

We are given:

[tex]n_1=1\\M_1=?\\V_1=10.0mL\\n_2=1\\M_2=0.1M\\V_2=7.2mL[/tex]

Putting values in above equation, we get:

[tex]1\times M_1\times 10.0=1\times 0.1\times 7.2\\\\M_1=0.072M[/tex]

To calculate pH of gastric juice:

molarity of [tex]H^+[/tex] = 0.072

[tex]pH=-log[H^+][/tex]

[tex]pH=-log(0.072)=1.14[/tex]

Thus the pH of the gastric juice is 1.14

The pH of the gastric juice is 1.14

We'll begin by calculating the molarity of the HCl needed for the reaction.

HCl + NaOH —> NaCl + H₂O

From the balanced equation above,

The mole ratio of the acid, HCl (nA) = 1

The mole ratio of the base, NaOH (nB) = 1

  • From the question given above,

Molarity of base, NaOH (Mb) = 0.1 M

Volume of base, NaOH (Vb) = 7.2 mL

Volume of acid, HCl (Va) = 10 mL

Molarity of acid, HCOOH (Ma) =?

MaVa / MbVb = nA/nB

(Ma × 10) / (0.1 × 7.2) = 1

(Ma × 10) / 0.72 = 1

Cross multiply

Ma × 10 = 0.72

Divide both side by 10

Ma = 0.72 / 10

Ma = 0.072 M

  • Next, we shall determine the concentration of the hydrogen ion in the solution

HCl (aq) —> H⁺(aq) + Cl¯(aq)

From the balanced equation above,

1 mole of HCl contains 1 mole of H⁺.

Therefore,

0.072 M HCl will also contain 0.072 M H⁺

  • Finally, we shall determine the pH.

Hydrogen ion concentration, [H⁺] = 0.072 M

pH =?

pH = –Log [H⁺]

pH = –Log 0.072

pH = 1.14

Thus, the pH of the gastric juice is 1.14

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