A.Determine the pH of the solution.
a solution that is 1.17% HCl by mass (Assume a density of 1.01 g/mL for the solution.)
B. Amphetamine (C9H13N) is a weak base with a pKb of 4.2. Calculate the pH of a solution containing an amphetamine concentration of 279 mg/L.
A.
1.17% by mass means 1.17g HCl/100 g soln.
mols HCl = grams/molar mass
Convert 100 g to mL using density.
Then M = mols/L
B. To save typing let's call amphetamine BNH2. M BNH2 = 0.279/molar mass = ?
..........BNH2 + HOH ==> BNH3^+ + OH^-
I.........?..............0.........0
C........-x..............x.........x
E.........?-x.............x.........x
Substitute from the ICE chart into the Kb expression for amphetamine and solve for x = OH^-, then convert that to pH.
To determine the pH of a solution, we need to understand the properties of the given substances and make use of relevant formulas.
A. Determining the pH of a solution of HCl:
1. Calculate the molarity (M) of HCl in the solution:
- Mass percent = (mass of solute / mass of solution) * 100
- Mass of HCl in the solution = (1.17 g / 100 g) * 1.17% (mass of solution is 100 g because it is given as a percentage)
- Density = mass / volume -> volume = mass / density = 1.17 g / 1.01 g/mL = 1.158 mL
- Molarity = (mass of HCl in grams / molar mass of HCl) / volume in liters
- Molar mass of HCl = 1 g/mol + 35.5 g/mol = 36.5 g/mol
- Molarity = (1.17 g / 36.5 g/mol) / (1.158 mL / 1000 mL/L) = 3.21 M
2. Since HCl is a strong acid, it ionizes completely in water, producing H+ ions.
The concentration of H+ ions in the solution is equal to the molarity of HCl, which in this case is 3.21 M.
3. Calculate the pH using the formula: pH = -log[H+]
- pH = -log(3.21) = 0.494
Therefore, the pH of the solution is approximately 0.494.
B. Determining the pH of a solution containing amphetamine:
1. Calculate the concentration (in moles per liter) of amphetamine in the solution:
- Concentration = mass of amphetamine / molar mass of amphetamine
- Mass of amphetamine = 279 mg = 0.279 g
- Molar mass of amphetamine = (9 * atomic mass of carbon) + (13 * atomic mass of hydrogen) + (1 * atomic mass of nitrogen)
- Atomic mass of carbon = 12.01 g/mol, atomic mass of hydrogen = 1.01 g/mol, atomic mass of nitrogen = 14.01 g/mol
- Molar mass of amphetamine = (9 * 12.01) + (13 * 1.01) + 14.01 = 135.19 g/mol
- Concentration = 0.279 g / (135.19 g/mol * (1 L / 1000 mL))
- Concentration = 0.279 g / 0.13519 mol = 2.062 M
2. Calculate the pOH using the formula: pOH = -log[OH-] (since amphetamine is a weak base):
- pKb = -log(Kb) -> Kb = 10^(-pKb)
- Kb = 10^(-4.2) = 6.31 x 10^(-5)
- OH- concentration = sqrt(Kb * concentration of amphetamine)
- OH- concentration = sqrt((6.31 x 10^(-5)) * (2.062))
3. Determine the concentration of H+ ions using the Kw formula: Kw = [H+][OH-] = 1 x 10^(-14)
- H+ concentration = Kw / OH- concentration
4. Calculate the pH using the formula: pH = -log[H+]
- pH = -log(H+ concentration)
By following these steps, you can calculate the pH of the amphetamine solution.