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In an acid-base titration, the net ionic equation simplifies the chemical reaction to show only the species that undergo a change. When potassium hydroxide (KOH) reacts with hydrobromic acid (HBr), we focus on the exchange of ions. KOH dissociates in water to form K鈦� and OH鈦� ions, while HBr dissociates into H鈦� and Br鈦� ions.
The reaction between the hydroxide ions (OH鈦�) from KOH and the hydrogen ions (H鈦�) from HBr forms water (H鈧侽).
This can be represented by the net ionic equation:

• OH鈦�(aq) + H鈦�(aq) 鈫� H鈧侽(l)

Neutralization takes place as the acid and base react to form water, highlighting the essential components of the acid-base reaction.

The equivalence point in a titration marks the moment when equal numbers of moles of acid and base have reacted. At this juncture, all the HBr has reacted with KOH, meaning every H鈦� ion has found an OH鈦� ion. Importantly, the solution now contains neither excess acid nor excess base.
What remains in the solution are:

• Potassium ions (K鈦�)
• Bromide ions (Br鈦�)
• Water (H鈧侽)

These leftover ions do not react further, as they are spectator ions. The equivalence point of a strong acid and strong base reaction leads to a neutral pH, typically around 7, due to the absence of strong acidic or basic characters among the products.

The pH of a solution in a titration changes as one moves through the following stages: beginning, halfway to the equivalence point, and at equivalence point.
**Before Any KOH is Added:**

- The pH of HBr (being a strong acid) is given by the concentration of H鈦� ions. - Here, \[ ext{pH} = -\log([0.257]) \approx 0.59 \\]**Halfway to Equivalence Point:**

- Half of the acid is neutralized, the solution consists of partially neutralized acid leading to: \[\text{pH} = -\log([\frac{0.257}{2}]) \approx 1.29\]**At Equivalence Point:**

- Complete neutralization results in a pH of 7. - This indicates a neutral solution, characteristic of reactions between strong acids and bases as no excess hydronium or hydroxide ions remain.

Molarity (M) measures the concentration of a solution in terms of moles of solute per liter of solution, while volume is typically measured in milliliters (mL) or liters in a titration.
To determine the volume of KOH needed to reach the equivalence point:
- Use the relationship: \[ \text{moles of } OH鈦� = \text{moles of } H鈦� \] - Given the molarities and the volume of acid, this relationship can be rewritten as:

• \( V_{KOH} \times C_{KOH} = V_{HBr} \times C_{HBr} \)
• \( V_{KOH} = \frac{V_{HBr} \times C_{HBr}}{C_{KOH}} \)

- Plugging in the values,\[ V_{KOH} = \frac{35.00 \mathrm{~mL} \times 0.257 \mathrm{M}}{0.1375 \mathrm{M}} \approx 64.73 \mathrm{~mL}\]This calculation enables us to predict and measure the exact volume required to achieve equivalence, ensuring all the acid is perfectly neutralized by the base.