Unit 3 Equilibrium Formulas/Calculations

Question 1

Which pHs are considered acidic?

Answer 1

1-6 acidic

Question 2

Which pH is neutral?

Answer 2

7

Question 3

Which pHs are considered basic?

Answer 3

8-14

Question 4

How do you calculate pH?

Answer 4

-log [H3O+]

negative log of the concentration of hydronium ions

Question 5

What is the pH of a solution of 0.004 moles/litre of H3O+?

Answer 5

pH = 2.4

Question 6

What is the pH of solution of 0.00000009 moles/litre of H3O+?

Answer 6

pH = 7.0

Question 7

pH + pOH = ?

Answer 7

14

Question 8

If pH is a measure of how acidic something is, what is pOH a measure of?

Answer 8

how basic something is

Question 9

How do you calculate pOH?

Answer 9

pOH = -log [OH-]

negative log of the concentration of hydroxide ions

Question 10

If the pH of a solution is 5, what is the pOH?

Answer 10

14-5 = pOH = 9

Question 11

How do you calculate the [H3O+] from pH?

Answer 11

[H3O+] = 10^-pH

Question 12

How do you calculate the [OH-] from pOH?

Answer 12

[OH-] = 10^-pOH

Question 13

If the pH is 4.3, what is the [H3O+]?

Answer 13

10^-4.3 = 5.0 x 10^-5 mol/L

Question 14

If the pH is 4.3, what is the [OH-]?

Answer 14

14-4.3 –> pOH = 9.7

10^-9.7 = [OH-] = 2.0x10^-10 mol/L

Question 15

HA + H2O –> A- + H3O+
is a generic acid reacting with water reaction
How do you calculate Ka?

Answer 15

Ka = ([H3O+][A-])/[HA]

Question 16

B- + H2O –> HB + OH-
is a generic base reacting with water reaction
How do you calculate Kb?

Answer 16

Kb = ([HB][OH-])/[B-]

Question 17

For reaction:
N2 + 3H2 –> 2NH3
Write the Kc (equilibrium expression)

Answer 17

Kc = ([NH3]^2)/([N2]^1 [H2]^3)

note: coefficient become exponents in the Kc expression

Question 18

How do you calculate concentration?

Answer 18

c = n/v = moles/volume

Question 19

How do you calculate moles?

Answer 19

n = m/M = mass/Molar Mass

Question 20

Kw = two things multiplying, what are they?

Answer 20

Kw = 1x10^-14 = Ka x Kb

Question 21

Using Kw, what is the Kb for the conjugate base of oxalic acid?

Answer 21

Kb = Kw/Ka = (1x10^-14)/(5.6x10^-2) = 1.78x10^-13

Note: K (equilibrium constants don’t have units)

Question 22

If you dilute a solution (i.e. add more water), the concentration changes. What is the formula for calculating this?

Answer 22

C1V1 = C2V2

Question 23

500mL of 0.2 mol/L solution is diluted to 700mL. What is the new concentration?

Answer 23

(500mL)(0.2mol/L) = x (700mL)
x = 0.14 mol/L

Question 24

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?

Answer 24

C1V1 = C2V2 since HCl and NaOH react 1:1 (otherwise you would use stoich)
volume of 1.25L

Question 25

Spectator ions

Answer 25

answer