Need help with this equilibrium question

Question

need help solving this question with steps

5. Determine the hydronium ion concentration and hydroxide ion concentration in each solution.

A) 0.95 mol/L hydrobromic acid. (2 marks)

B)  0.012 mol/L calcium hydroxide (4 marks)

Answer 1

A) you are given the concentration of HBr acid as 0.95 M

HBr is one of the seven inorganic strong acids that dissociates completely into its ions,

HBr -----> H3O+ + Br-

this means HBr with a Molarity of 0.95M has a H3O+ concentration of 0.95 mol/L (M)

To find the {OH-} you take the following steps:

1) find the pH of the HBr, convert to that to the pOH and then take the antilog of the -pOH to obtain the {OH-}

pH = -log {H+} = -log 0.95 = 0.022

pH + pOH = 14: 0.022 + pOH = 14

pOH = 14 - 0.022 = 13.978

{OH-} = antilog -pOH

{OH-} = antilog -13.978 = 1.052 x 10-14 M

B) Given the Molarity of Ca(OH)2 = 0.012 M

Ca(OH)2 is a strong base meaning it dissociates completely into its respective ions,

Ca(OH)2-----> Ca+2 + 2OH-

Note that for every one mole of Ca(OH)2 you form one mole of Ca+2 and 2 moles of OH-

Therefore you must multiply the Molarity of Ca(OH)2 by x 2 to obtain the Molarity of {OH-}

{OH-} = 0.012 x 2 = 0.024 M

1) To find the H3O+ concentration, {H+}, the steps are very similar to part A)

You find the pOH, subtract that number from 14 to obtain the pH, then take the antilog of the -pH and that will give you your {H3O+}

pOH = -log {OH-}

pOH = -log 0.024 = 1.62

now use the relationship: pH + pOH = 14

1.62 + pH = 14

pH = 14 - 1.62 = 12.38

final step: take the antilog of the -pH to get the {H3O+}

{H3O+} = antilog -12.38 = 4.169 x 10-13 M (mol/L)