A 20.0 mL sample of gastric juice was taken from a patient suspected of having hypochloridia (low stomach acid). The sample was taken several hours after a meal so there was no ingested food or drink, and it was assumed no buffers were present. The sample required 6.3 mL of 0.0011 M NaOH to titrate the sample to neutrality.
What was the pH of the gastric juice?
mols NaOH = M x L = ?
mols HCl(in the gastric juice) = mols NaOH
M HCl = mols HCl/L HCl. L = 0.020.
Then convert M to pH.
pH = -log(H^+).
-1.70
12
To determine the pH of the gastric juice, we can first calculate the number of moles of NaOH that reacted with the gastric juice. Then, we can use this information to determine the concentration of OH- ions in the solution, which will allow us to calculate the pOH and pH of the gastric juice.
1. Calculate the number of moles of NaOH:
- Given volume of NaOH solution used: 6.3 mL
- Convert mL to L: 6.3 mL = 0.0063 L
- Concentration of NaOH solution: 0.0011 M
- Use the formula n = M * V to calculate the number of moles: n(NaOH) = 0.0011 M * 0.0063 L
2. Determine the number of moles of H+ ions in gastric juice:
- According to the balanced equation for the reaction between NaOH and HCl (the main component of gastric juice), the ratio of NaOH to HCl is 1:1. Therefore, the number of moles of NaOH is equal to the number of moles of H+ ions in the gastric juice.
3. Calculate the number of moles of H+ ions in the gastric juice:
- n(H+) = n(NaOH) = 0.0011 M * 0.0063 L
4. Calculate the concentration of OH- ions in the solution:
- In a neutral solution, the concentration of H+ ions is equal to the concentration of OH- ions. Therefore, the concentration of OH- ions in the gastric juice sample is also 0.0011 M.
5. Calculate the pOH of the gastric juice:
- Use the formula pOH = -log[OH-] to calculate the pOH: pOH = -log(0.0011)
6. Calculate the pH of the gastric juice:
- The pH of a solution can be calculated using the formula pH = 14 - pOH: pH = 14 - pOH
By following these steps and performing the necessary calculations, you can determine the pH of the gastric juice.