When 25ml of 0.10 mol/l HBr is titrated with 0.10 mol/l NaOH, what is the pH at the equivalence point?
Whenever you titrate a strong acid with a strong base, the pH at the equivalence point is 7.00.
Whenever you titrate a strong acid with a weak base, the pH at the equivalence point is less than 7.00.
Whenever you titrate a weak acid with a strong base, the pH at the equivalence point is greater than 7.00.
Now, you will say: why?
HBr(aq) + NaOH(aq) -----> NaBr(aq) + H2O(l)
0.10 M ...... 0.10 M
Strong acid ionizes completely
HBr(aq) -------> H+(aq) + Br-(aq)
0.10 M ............. 0.10 M
Strong base dissociates completely:
NaOH(aq) -------> Na+(aq) + OH-(aq)
0.10 M .................................... 0.10 M
At the equivalence point:
Mole H+ = Mole OH-
After neutralization the solution contains Na+ and Br- ions. Since these ions cannot hydrolize ( react with water to produce H+ or OH-), the solution becomes completely neutral.
You will have the salt of a strong base and a strong acid; therefore, the pH will be 7.0
To determine the pH at the equivalence point, we need to calculate the number of moles of hydrochloric acid (HBr) and sodium hydroxide (NaOH) present.
Step 1: Determine the number of moles of HBr:
Molarity (M) = moles/liters
moles = Molarity × volume (in liters)
Moles of HBr = 0.10 mol/l × 0.025 L = 0.0025 moles
Step 2: Determine the number of moles of NaOH:
The balanced equation for the reaction between HBr and NaOH is:
HBr + NaOH → NaBr + H2O
From the equation, we can see that the stoichiometric ratio between HBr and NaOH is 1:1.
Hence, the number of moles of NaOH will also be 0.0025 moles.
Step 3: The equivalence point occurs when the moles of HBr equal the moles of NaOH.
At the equivalence point, all HBr has reacted with NaOH to form sodium bromide (NaBr) and water (H2O).
Step 4: The pH at the equivalence point will depend on the final solution formed.
Since HBr is a strong acid and NaOH is a strong base, the final solution will be neutral. Therefore, the pH at the equivalence point will be 7.
To determine the pH at the equivalence point, we first need to understand the reaction that occurs during the titration.
HBr reacts with NaOH in a 1:1 stoichiometric ratio to produce water (H2O) and a sodium bromide (NaBr) salt:
HBr + NaOH → NaBr + H2O
At the equivalence point, the moles of acid (HBr) equal the moles of base (NaOH). Since the concentration of both solutions is 0.10 mol/l, the volume ratio is also equal to the mole ratio.
Given that 25 ml of 0.10 mol/l HBr is titrated, the number of moles of HBr can be calculated as follows:
moles of HBr = concentration × volume = 0.10 mol/l × 0.025 l (25 ml converted to liters) = 0.0025 moles
Since the reaction is 1:1, the number of moles of NaOH required to reach the equivalence point is also 0.0025 moles.
Now, to find the volume of 0.10 mol/l NaOH required to reach the equivalence point, we divide the number of moles by the concentration:
volume of NaOH = moles / concentration = 0.0025 moles / 0.10 mol/l = 0.025 l (25 ml)
As you can observe, the volume of NaOH required to reach the equivalence point is the same as the volume of HBr initially taken. Therefore, the total volume at the equivalence point is 25 ml + 25 ml = 50 ml.
Now, let's consider the reaction at the equivalence point. Since equal volumes of strong acid (HBr) and strong base (NaOH) are mixed, the resulting solution contains the salt NaBr along with water. Therefore, the pH at the equivalence point will be neutral, i.e., pH 7.