Question
If 50 mL of 0.02 M HCl is added to 950 mL of $H_2O$, then the pH of the final solution will be _________
To determine the pH of the solution after adding 50 mL of 0.02 M HCl to 950 mL of water, follow these steps:
Step 1: Calculate the total volume of the solution.
The combined volume is 50 mL of HCl + 950 mL of water = 1000 mL.
Step 2: Calculate the moles of HCl added.
The molarity (M) of HCl is given as 0.02 M, which means there are 0.02 moles in 1000 mL of solution. Therefore, in 50 mL, moles = 0.02 mol/L × 0.050 L = 0.001 moles HCl.
Step 3: Determine the concentration of H+ ions in the final solution.
Since HCl is a strong acid, it completely dissociates in water, contributing 0.001 moles of H+ in the total volume of 1000 mL (1 L), so [H+] = 0.001 moles/L = 0.001 M.
Step 4: Calculate the pH of the solution.
pH = -log[H+] = -log(0.001) = 3.
This pH value falls within the range 3 to 3, confirming correctness.
Step 1: Calculate the total volume of the solution.
The combined volume is 50 mL of HCl + 950 mL of water = 1000 mL.
Step 2: Calculate the moles of HCl added.
The molarity (M) of HCl is given as 0.02 M, which means there are 0.02 moles in 1000 mL of solution. Therefore, in 50 mL, moles = 0.02 mol/L × 0.050 L = 0.001 moles HCl.
Step 3: Determine the concentration of H+ ions in the final solution.
Since HCl is a strong acid, it completely dissociates in water, contributing 0.001 moles of H+ in the total volume of 1000 mL (1 L), so [H+] = 0.001 moles/L = 0.001 M.
Step 4: Calculate the pH of the solution.
pH = -log[H+] = -log(0.001) = 3.
This pH value falls within the range 3 to 3, confirming correctness.
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Important Questions from Chemical Biology {p}K_a Henderson Hasselbalch
- The equilibrium dissociation constant of acetic acid is $1.74 \times 10^{-5}$ $M$. The $pK_a$ of acetic acid (rounded off to one decimal place) is ________.
- The ionic product of water at $40$ °C is $2.92 \times 10^{-14}$ $M^2$. The pH of water at $40$ °C is ________ (rounded off to 2 decimal places).
- In a lactic acid solution at pH $4.8$, the concentrations of lactic acid and lactate are $0.01$ M and $0.087$ M, respectively. The calculated pKa of lactic acid is ________ (Round off to one decimal place)
An aqueous solution of aspirin (HA) is prepared at pH 7.4. The ratio of concentration of $A^-$ and HA at equilibrium is ________ (round off to the nearest integer).
Given: $K_a$ of aspirin is $3.98 \times 10^{-4}$
One litre of phosphate buffer was prepared by adding 208 grams of $Na_2HPO_4$ (Mol. wt. 142) and 71 grams of $NaH_2PO_4$ (Mol. wt. 120) in water. If the $pK_a$ for the dissociation of $H_2PO_4^-$ into $HPO_4^{2–}$ and $H^+$ is 6.86, the pH of the buffer will be __________
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