Nā nīnau hoʻohālike e kūkākūkā ana i ka pH o nā waikawa ikaika a me nā kumu ikaika
ʻO ka pH, a i ʻole ka hiki o ka hydrogen, he ana ia o ka acidity a i ʻole ka alkalinity o kahi hopena. Loaʻa ka pālākiō pH mai ka 0 a i ka 14, me nā helu ma lalo o 7 e hōʻike ana i kahi hopena acidic, nā helu ma luna o 7 e hōʻike ana i kahi hopena kumu, a ʻo 7 e hōʻike ana i kahi hopena neutral. Ma kēia ʻatikala, e kūkākūkā mākou i kekahi mau pilikia hoʻohālike e pili ana i ka pH o nā waikawa ikaika a me nā kumu ikaika, me kā lākou mau hopena.
Pendahuluan
Nā Manaʻo Kumu o ka pH
ʻO ka pH kahi ana i hoʻohana ʻia e hoʻoholo ai i ka acidity a i ʻole alkalinity o kahi hopena e pili ana i ka nui o nā ion hydrogen (H+). ʻO ke ʻano kumu no ka helu ʻana i ka pH penei:
\[ \kikokikona{pH} = -\log{[H^+]} \]
Ma kahi o [H+] ka nui o ka ion hydrogen ma mol/L.
Ma kekahi ʻaoʻao, no nā hopena kumu (nā kumu ikaika), hiki iā mākou ke helu mua i ka pOH a laila hoʻololi iā ia i ka pH me ka hoʻohana ʻana i kēia ʻano hana:
\[ \kikokikona{pOH} = -\log{[OH^-]} \]
\[ \kikokikona{pH} = 14 – \kikokikona{pOH} \]
ʻAkika Ikaika vs. ʻAkika Nawaliwali
ʻO ka waikawa ikaika kahi waikawa e hoʻokahe piha i loko o ka wai. ʻO ke ʻano kēia, ua like ka nui o nā ion H+ i loko o ka wai me ka nui o ka waikawa ponoʻī. ʻO nā hiʻohiʻona o nā waikawa ikaika ʻo HCl (hydrochloric acid), HNO3 (nitric acid), a me H2SO4 (sulfuric acid).
I ka hoʻohālikelike ʻana, ʻaʻole i hoʻokahe piha nā waikawa nāwaliwali i loko o ka hopena, no laila ʻoi aku ka paʻakikī o kā lākou helu ʻana i ka pH a koi ʻia ka manaʻo o kahi kūpaʻa acidity (Ka).
Kumu Ikaika vs Kumu Nawaliwali
E like me nā waikawa ikaika, hoʻohui pū nā kumu ikaika i ka ionization i loko o ka wai. ʻO nā hiʻohiʻona o nā kumu ikaika ʻo NaOH (sodium hydroxide) a me KOH (potassium hydroxide).
Hoʻokaʻawale hapa ʻia nā kumu nāwaliwali a koi ʻia ka manaʻo o kahi kūpaʻa kumu (Kb) e helu ai i ka pH.
Nā Nīnau Laʻana a me ke Kūkākūkā
Laʻana Nīnau 1: ʻAkika Ikaika
> E helu i ka pH o kahi hopena HCl 0.01 M.
Kūkākūkā:
No ka mea he waikawa ikaika ʻo HCl, e hoʻoheheʻe loa ia i loko o ka hopena.
\[ \kikokikona{HCl} \rightarrow \kikokikona{H}^+ + \kikokikona{Cl}^- \]
ʻO ka nui o nā ion H+ i loko o ka hopena e like ia me ka nui o ka HCl i hāʻawi ʻia, ʻo ia hoʻi ʻo 0.01 M.
\[ [H^+] = 0.01 \, \kikokikona{M} \]
Ke hoʻohana nei i ke ʻano pH:
\[ \text{pH} = -\log{[H^+]} = -\log{0.01} = -\log{10^{-2}} = 2 \]
No laila, ʻo ka pH o kahi hopena HCl 0.01 M he 2.
Laʻana Nīnau 2: Nā Kumu Ikaika
> E helu i ka pH o kahi hopena 0.001 M NaOH.
Kūkākūkā:
He kumu ikaika ʻo NaOH a e ionize loa ia i loko o ka hopena.
\[ \kikokikona{NaOH} \rightarrow \kikokikona{Na}^+ + \kikokikona{OH}^- \]
ʻO ka nui o nā OH- ions i loko o ka hopena ua like ia me ka nui o NaOH, ʻo ia hoʻi ʻo 0.001 M.
\[ [OH^-] = 0.001 \, \kikokikona{M} = 10^{-3} \, \kikokikona{M} \]
E helu mua i ka pOH:
\[ \kikokikona{pOH} = -\log[OH^-] = -\log{10^{-3}} = 3 \]
E hoʻololi i ka pOH i ka pH:
\[ \kikokikona{pH} = 14 – \kikokikona{pOH} = 14 – 3 = 11 \]
No laila, ʻo ka pH o kahi hopena 0.001 M NaOH he 11.
Laʻana Nīnau 3: Waikawa Sulfuric (H2SO4)
> E helu i ka pH o kahi hopena 0.01 M H2SO4.
Kūkākūkā:
He waikawa ikaika ʻo H2SO4 me ʻelua mau pae o ka ionization. ʻO ke kahua mua:
\[ \kikokikona{H2SO4} \rightarrow \kikokikona{H}^+ + \kikokikona{HSO4}^- \]
ʻO ka hopena o ka ionization pae mua e like me ka nui o ka H2SO4 o 0.01 M no kēlā me kēia H+ a me HSO4^-. Eia nō naʻe, hoʻopuka ka pae mua i ʻelua mau ion H+ mai hoʻokahi mole H2SO4.
No laila, ʻo ka huina [H+] e pālua i ka nui mua:
\[ [H^+] = 2 \times 0.01 = 0.02 \]
Ke hoʻohana nei i ke ʻano pH:
\[ \text{pH} = -\log{[H^+]} = -\log{0.02} = -\log{2 \times 10^{-2}} = -(\log{2} + \log{10^{-2}}) \]
No kou ʻike,
\[ \log{2} \approx 0.301 \]
No laila:
\[ \kikokikona{pH} = -(0.301 + (-2)) = 1.699 \]
No laila, ʻo ka pH o kahi hopena 0.01 M H2SO4 ma kahi o 1.699.
Laʻana Nīnau 4: Kumu Ikaika (Ca(OH)2)
> E helu i ka pH o kahi hopena 0.005 M Ca(OH)2.
Kūkākūkā:
He kumu ikaika ʻo Ca(OH)2 a hāʻawi kēlā me kēia mole i ʻelua mau iona OH-:
\[ \kikokikona{Ca(OH)2} \rightarrow \kikokikona{Ca}^{2+} + 2\kikokikona{OH}^- \]
ʻO ka nui o OH- e pālua i ka nui o Ca(OH)2 no ka mea ʻo kēlā me kēia mole o Ca(OH)2 e hana i ʻelua OH-. No laila,
\[ [OH^-] = 2 \times 0.005 = 0.01 \, \text{M} \]
E helu mua i ka pOH:
\[ \text{pOH} = -\log{[OH^-]} = -\log{0.01} = -\log{10^{-2}} = 2 \]
E hoʻololi i ka pOH i ka pH:
\[ \kikokikona{pH} = 14 – \kikokikona{pOH} = 14 – 2 = 12 \]
No laila, ʻo ka pH o kahi hopena 0.005 M Ca(OH)2 he 12.
Ka hopena
Ma kēia ʻatikala, ua kūkākūkā mākou pehea e helu ai i ka pH no kekahi mau hiʻohiʻona o nā hopena waikawa ikaika a me nā hopena kumu ikaika. E hoʻomanaʻo no nā waikawa ikaika a i ʻole nā kumu, ke manaʻo nei mākou ua hoʻohuihui piha ʻia lākou i loko o ka hopena. No laila, ʻo ka nui o nā ion H+ no kahi waikawa ikaika a me nā ion OH- no kahi kumu ikaika e like me ka nui mua o ka waikawa a i ʻole ke kumu, ma hope o ka hoʻoponopono ʻana no nā kumu stoichiometric inā pono. Hoʻomaʻalahi kēia i nā helu pH me ka hoʻohana ʻana i nā ʻano pH a me pOH kumu.
He mea koʻikoʻi ka hoʻomaopopo ʻana i kēia manaʻo, ʻoi aku hoʻi i nā noi kemika, inā paha ma ka hale hana kemika, ʻoihana, a i ʻole ke ola o kēlā me kēia lā. Me ka hoʻomaʻamaʻa a me ka hoʻomaopopo paʻa, e lilo ka helu ʻana i ka pH o nā waikawa ikaika a me nā kumu i mea maʻalahi.
