A solution of NaOH(aq) contains 6.2 g of NaOH(s) per 100.0 mL of solution. Calculate the pH and the pOH of the solution at 25 °C.
moles NaOH = grams/molar mass
M = moles NaOH/L soln.
(OH^-) = M NaOH
pOH = -log(OH^-)
Use pH + pOH = pKw = 14 to convert pOH to pH.
Then convert pH to (H^+) by
pH = -log(H^+).
i didn't know ph could be greater than 14 and poh less than 0
It can.
For example, if M HCl = 0.1M, then (H^+) = 0.1 and pH = 1
If M HCl = 1.0, then (H^+) = 1.0M and pH = -log(1.0) = 0
If M HCl = 10.0, then (H^+) = 10.0M and pH = -log(10) = -log(1) = -1.
We usually work with pH values for solns in the 0.1 and smaller range; therefore, the pH is always greater than zero and positive. In fact, when the pH scale was first devised, the negative sign was put in the definition (pH = -log(H^+) for the expressed purpose of making the number a positive number since the log of numbers less than 1 are negative.
Oh, NaOH, you're so basic! But let's try to calculate the pH and pOH for you. To start, we need to convert grams into moles. The molar mass of NaOH is 40.0 g/mol, so we divide 6.2 g by 40.0 g/mol to get 0.155 mol.
Now, we'll convert mL into L. Since there are 1000 mL in 1 L, 100.0 mL becomes 0.1000 L.
Using the concentration formula, we divide the moles of NaOH by the volume in liters to get the concentration of NaOH. So, 0.155 mol / 0.1000 L gives us a concentration of 1.55 M.
Since NaOH is a strong base, it completely dissociates in water, giving us equal amounts of Na+ and OH- ions. So, the concentration of OH- ions is also 1.55 M.
Now, let's calculate the pOH. The pOH is defined as the negative logarithm (base 10) of the OH- concentration. So, taking the negative logarithm of 1.55 gives us a pOH of -0.810.
Since pH + pOH = 14, we can subtract the pOH from 14 to find the pH. Therefore, the pH is 14 - 0.810, which equals 13.19.
So, the pH of the solution is 13.19, and the pOH is -0.810. I hope that puts a smile on your face!
To calculate the pH and pOH of the solution, we need to first determine the concentration of hydroxide ions (OH-) in the solution.
Step 1: Calculate the moles of NaOH:
Molar mass of NaOH = 22.99 g/mol + 16.00 g/mol + 1.01 g/mol = 39.99 g/mol
Moles of NaOH = mass / molar mass
Moles of NaOH = 6.2 g / 39.99 g/mol = 0.155 mol
Step 2: Calculate the concentration of NaOH:
Concentration (in moles per liter) = moles / volume (in liters)
Volume = 100.0 mL = 100.0 mL * (1 L / 1000 mL) = 0.100 L
Concentration of NaOH = 0.155 mol / 0.100 L = 1.55 M
Step 3: Calculate the concentration of OH- ions:
Since NaOH is a strong base, it dissociates fully in water, so the concentration of OH- ions is the same as the concentration of NaOH: 1.55 M.
Step 4: Calculate the pOH:
pOH = -log10[OH-]
pOH = -log10(1.55) ≈ 0.81
Step 5: Calculate the pH:
The sum of pH and pOH is always equal to 14 at 25 °C.
pH + pOH = 14
pH = 14 - 0.81 ≈ 13.19
Therefore, the pH of the solution at 25 °C is approximately 13.19, and the pOH is approximately 0.81.