1.14g of sodium bicarbonate (NaHCO3)is dissolved in 500 mL H2O. What is the Ph of the solution? Assume constant volume.
I have been trying to work this out with no success - any help would be great - Thanks
Without deriving the equation, the formula for what you want is
(H^+) = sqrt(k1k2) or
pH = 1/2(pK1 + pK2)
The answer for NaHCO3 is about 8.3 or so.
To determine the pH of a solution, we need to know the concentration of hydrogen ions (H+) in the solution. The concentration of H+ can be found by calculating the concentration of the hydronium ion (H3O+), which is a measure of acidity.
In this case, we have 1.14g of sodium bicarbonate (NaHCO3) dissolved in 500 mL of water. To find the concentration of H3O+ ions, we need to first calculate the number of moles of NaHCO3 and then use the balanced chemical equation of its dissociation in water.
The molar mass of NaHCO3 is:
Na = 22.99 g/mol
H = 1.01 g/mol
C = 12.01 g/mol
O = 16.00 g/mol
So, the molar mass of NaHCO3 is:
22.99 + 1.01 + 12.01 + (3 × 16.00) = 84.01 g/mol
To find the number of moles of NaHCO3, we divide the mass of NaHCO3 by its molar mass:
1.14 g / 84.01 g/mol = 0.0136 mol
Now, looking at the balanced chemical equation for the dissociation of NaHCO3:
NaHCO3 ⇌ Na+ + HCO3-
We can see that NaHCO3 dissociates into Na+ and HCO3-. In water, HCO3- acts as a weak base and reacts with water to form H3O+ ions and CO32- ions:
HCO3- + H2O ⇌ H3O+ + CO32-
However, since the question assumes constant volume, we can assume that the HCO3- ions are present in excess, and the conversion to H3O+ ions is complete. Therefore, the concentration of HCO3- ions is equal to the concentration of H3O+ ions.
The concentration of H3O+ (and HCO3-) ions can be calculated using the following formula:
Concentration (mol/L) = (moles of solute) / (volume of solution in liters)
In this case, the volume of the solution is given as 500 mL, which is equal to 0.5 L. Therefore:
Concentration of H3O+ ions = 0.0136 mol / 0.5 L = 0.0272 mol/L
To find the pH of the solution, we can use the equation:
pH = -log[H3O+]
Plugging in the value for the concentration of H3O+ we calculated earlier:
pH = -log(0.0272) ≈ 1.57
Therefore, the pH of the solution is approximately 1.57.