Ngā Tauira Pātai e Matapaki ana i te pH o ngā Waikawa Kaha me ngā Pākawa Kaha
Ko te pH, te pūmanawa rānei o te hauwai, he ine i te waikawa, i te kawakore rānei o tētahi otinga. Kei waenga i te 0 ki te 14 te tauine pH, ko ngā tau i raro iho i te 7 e tohu ana i tētahi otinga waikawa, ko ngā tau i runga ake i te 7 e tohu ana i tētahi otinga taketake, ā, ko te 7 e tohu ana i tētahi otinga kūpapa. I roto i tēnei tuhinga, ka matapakihia e mātou ētahi tauira raruraru e pā ana ki te pH o ngā waikawa kaha me ngā turanga kaha, me ō rātou otinga.
Pendahuluan
Ngā Ariā Taketake o te pH
Ko te pH he mehua e whakamahia ana hei whakatau i te waikawa, te kawakore rānei o tētahi otinga i runga i te kukū o ngā iona hauwai (H+). Ko te tātai taketake mō te tatau i te pH ko:
\[ \text{pH} = -\log{[H^+]} \]
Ko [H+] te kukū o te katote hauwai i roto i te mol/L.
I tētahi atu taha, mō ngā otinga taketake (ngā turanga kaha), ka taea e tātou te tatau i te pOH i te tuatahi, kātahi ka huri ki te pH mā te whakamahi i te tātai e whai ake nei:
\[ \text{pOH} = -\log{[OH^-]} \]
\[ \kuputuhi{pH} = 14 – \kuputuhi{pOH} \]
Waikawa Kaha me te Waikawa Ngoikore
Ko te waikawa kaha he waikawa e whakakōkī katoa ana i roto i te wairewa. Ko te tikanga o tēnei ko te kukū o ngā katote H+ i roto i te wairewa he rite ki te kukū o te waikawa tonu. Ko ngā tauira o ngā waikawa kaha ko te HCl (waikawa hauwaiora), te HNO3 (waikawa hauota), me te H2SO4 (waikawa whanariki).
He rerekē, kāore ngā waikawa ngoikore e tino ionize i roto i te wairewa, nō reira he uaua ake ā rātou tataunga pH, ā, me whakamahi i te ariā o te pūmau waikawa (Ka).
Pūtake Kaha vs Pūtake Ngoikore
Pērā i ngā waikawa kaha, ka tino ionize hoki ngā turanga kaha i roto i te wairewa. Ko ngā tauira o ngā turanga kaha ko te NaOH (hauwai konutai) me te KOH (hauwai pāhare pākawa).
He wāhanga noa iho o te ionization o ngā turanga ngoikore, ā, me whakamahi te ariā o te pūmau taketake (Kb) hei tatau i te pH.
Ngā Pātai Tauira me te Kōrero
Tauira Pātai 1: Waikawa Kaha
> Tātaihia te pH o tētahi otinga HCl 0.01 M.
Kōrero:
Nā te mea he waikawa kaha te HCl, ka whakakōkī katoatia i roto i te wairewa.
\[ \kuputuhi{HCl} \rightarrow \kuputuhi{H}^+ + \kuputuhi{Cl}^- \]
Ka rite te kukū o ngā katote H+ i roto i te otinga ki te kukū o te HCl i whakaratohia, arā, 0.01 M.
\[ [H^+] = 0.01 \, \kuputuhi{M} \]
Mā te whakamahi i te tātai pH:
\[ \text{pH} = -\log{[H^+]} = -\log{0.01} = -\log{10^{-2}} = 2 \]
Nō reira, ko te pH o te otinga HCl 0.01 M he 2.
Tauira Pātai 2: Ngā Pūtake Kaha
> Tātaihia te pH o tētahi otinga NaOH 0.001 M.
Kōrero:
He turanga kaha te NaOH, ā, ka whakaionia katoatia i roto i te wairewa.
\[ \text{NaOH} \rightarrow \text{Na}^+ + \text{OH}^- \]
He rite te kukū o ngā iona OH- i roto i te otinga ki te kukū o te NaOH, arā, 0.001 M.
\[ [OH^-] = 0.001 \, \kuputuhi{M} = 10^{-3} \, \kuputuhi{M} \]
Tātaihia te pOH i te tuatahi:
\[ \text{pOH} = -\log[OH^-] = -\log{10^{-3}} = 3 \]
Tahurihia te pOH ki te pH:
\[ \kuputuhi{pH} = 14 – \kuputuhi{pOH} = 14 – 3 = 11 \]
Nō reira, ko te pH o te otinga NaOH 0.001 M he 11.
Tauira Pātai 3: Waikawa Whāwhā (H2SO4)
> Tātaihia te pH o tētahi otinga H2SO4 0.01 M.
Kōrero:
He waikawa kaha te H2SO4, e rua ngā wāhanga o te whakakōkī. Ko te wāhanga tuatahi:
\[ \kuputuhi{H2SO4} \rightarrow \kuputuhi{H}^+ + \kuputuhi{HSO4}^- \]
Ko te hua o te whakakoi i te wāhanga tuatahi he rite ki te kukū H2SO4 o te 0.01 M mō ia H+ me te HSO4^-. Heoi, ka puta i te wāhanga tuatahi e rua ngā katote H+ mai i te ngota H2SO4 kotahi.
Nō reira, ko te tapeke [H+] ka rua te nui o te kukū tīmatanga:
\[ [H^+] = 2 \whakareatia ki te 0.01 = 0.02 \]
Mā te whakamahi i te tātai pH:
\[ \text{pH} = -\log{[H^+]} = -\log{0.02} = -\log{2 \times 10^{-2}} = -(\log{2} + \log{10^{-2}}) \]
Hei whakamōhio atu ki a koe,
\[ \log{2} \tata ki te 0.301 \]
Nā reira:
\[ \text{pH} = -(0.301 + (-2)) = 1.699 \]
Nō reira, ko te pH o te otinga 0.01 M H2SO4 he tata ki te 1.699.
Tauira Pātai 4: Pūtake Kaha (Ca(OH)2)
> Tātaihia te pH o tētahi otinga 0.005 M Ca(OH)2.
Kōrero:
He turanga kaha a Ca(OH)2, ā, e rua ngā iona OH- ka puta mai i ia ngota:
\[ \text{Ca(OH)2} \rightarrow \text{Ca}^{2+} + 2\text{OH}^- \]
Ka rua te kukū o te OH- i te kukū o te Ca(OH)2 nā te mea e rua ngā OH- ka puta i ia ngota ngota o te Ca(OH)2. Nō reira,
\[ [OH^-] = 2 \times 0.005 = 0.01 \, \text{M} \]
Tātaihia te pOH i te tuatahi:
\[ \text{pOH} = -\log{[OH^-]} = -\log{0.01} = -\log{10^{-2}} = 2 \]
Tahurihia te pOH ki te pH:
\[ \kuputuhi{pH} = 14 – \kuputuhi{pOH} = 14 – 2 = 12 \]
Nō reira, ko te pH o te otinga 0.005 M Ca(OH)2 he 12.
Whakamutunga
I roto i tēnei tuhinga, kua matapakihia e mātou te huarahi ki te tatau i te pH mō ētahi tauira o ngā otinga waikawa kaha me ngā otinga turanga kaha. Kia maumahara, mō ngā waikawa kaha, ngā turanga kaha rānei, e whakaaro ana mātou kua tino whakakōkītia rātou i roto i te otinga. Nō reira, ko te kukū o ngā iona H+ mō te waikawa kaha me ngā iona OH- mō te turanga kaha ka ōrite ki te kukū tīmatanga o te waikawa, o te turanga rānei, i muri i te whakarerekētanga mō ngā āhuatanga stoichiometric mēnā e tika ana. Mā tēnei ka māmā ake ngā tataunga pH mā te whakamahi i ngā tātai pH me te pOH taketake.
He mea nui te mārama ki tēnei ariā, inā koa i roto i ngā mahi matū, ahakoa i roto i te taiwhanga matū, i te ahumahi, i te oranga o ia rā rānei. Mā te mahi me te māramatanga pakari, ka māmā noa te tatau i te pH o ngā waikawa me ngā kawakore kaha.
