Unit 3 Equilibrium Formulas/Calculations Flashcards
Which pHs are considered acidic?
1-6 acidic
Which pH is neutral?
7
Which pHs are considered basic?
8-14
How do you calculate pH?
-log [H3O+]
negative log of the concentration of hydronium ions
What is the pH of a solution of 0.004 moles/litre of H3O+?
pH = 2.4
What is the pH of solution of 0.00000009 moles/litre of H3O+?
pH = 7.0
pH + pOH = ?
14
If pH is a measure of how acidic something is, what is pOH a measure of?
how basic something is
How do you calculate pOH?
pOH = -log [OH-]
negative log of the concentration of hydroxide ions
If the pH of a solution is 5, what is the pOH?
14-5 = pOH = 9
How do you calculate the [H3O+] from pH?
[H3O+] = 10^-pH
How do you calculate the [OH-] from pOH?
[OH-] = 10^-pOH
If the pH is 4.3, what is the [H3O+]?
10^-4.3 = 5.0 x 10^-5 mol/L
If the pH is 4.3, what is the [OH-]?
14-4.3 –> pOH = 9.7
10^-9.7 = [OH-] = 2.0x10^-10 mol/L
HA + H2O –> A- + H3O+
is a generic acid reacting with water reaction
How do you calculate Ka?
Ka = ([H3O+][A-])/[HA]
B- + H2O –> HB + OH-
is a generic base reacting with water reaction
How do you calculate Kb?
Kb = ([HB][OH-])/[B-]
For reaction:
N2 + 3H2 –> 2NH3
Write the Kc (equilibrium expression)
Kc = ([NH3]^2)/([N2]^1 [H2]^3)
note: coefficient become exponents in the Kc expression
How do you calculate concentration?
c = n/v = moles/volume
How do you calculate moles?
n = m/M = mass/Molar Mass
Kw = two things multiplying, what are they?
Kw = 1x10^-14 = Ka x Kb
Using Kw, what is the Kb for the conjugate base of oxalic acid?
Kb = Kw/Ka = (1x10^-14)/(5.6x10^-2) = 1.78x10^-13
Note: K (equilibrium constants don’t have units)
If you dilute a solution (i.e. add more water), the concentration changes. What is the formula for calculating this?
C1V1 = C2V2
500mL of 0.2 mol/L solution is diluted to 700mL. What is the new concentration?
(500mL)(0.2mol/L) = x (700mL) x = 0.14 mol/L
5L of 0.1mol/L of HCl is reacted with NaOH. If the NaOH has a concentration of 0.4mol/L, how much of the NaOH do you need to neutralize the HCl?
C1V1 = C2V2 since HCl and NaOH react 1:1 (otherwise you would use stoich)
volume of 1.25L
Spectator ions
answer
