Me pēhea te hanga i tētahi otinga pūwero
Pendahuluan
He otinga matū te otinga pākawa e pupuri ana i te pH pumau ahakoa he iti noa te waikawa, te kawa rānei e tāpirihia ana. He mea nui ngā otinga pākawa i roto i ngā momo mara, tae atu ki te matū koiora, te rongoā, me ngā taiwhanga rangahau. Ka hipokina e tēnei tuhinga te hanga otinga pākawa, tae atu ki te māramatanga taketake mō te mahi a ngā otinga pākawa, ngā wāhanga e hiahiatia ana, me ngā mahi motuhake e whai wāhi ana.
Te Mārama ki ngā Otinga Pūwero
Ko te otinga parepare he takirua waikawa-pūtake honohono ka taea te mimiti i ngā iona H⁺, OH⁻ rānei e tāpirihia ana ki te otinga, ā, mā reira ka ārai i ngā huringa nui o te pH. E rua ngā momo matua o ngā otinga parepare:
1. Pūwero Waikawa: He mea hanga mai i te waikawa ngoikore me tōna tote (kei roto ko tōna turanga honohono). Hei tauira, he ranunga asam asetat (CH₃COOH) me te konutai ātete (CH₃COONa).
2. Pūwero Tūāpapa: He mea hanga mai i te tūāpapa ngoikore me tōna tote (kei roto ko tōna waikawa honohono). Hei tauira, he ranunga o te haukini (NH₃) me te haukini pūhaumāota (NH₄Cl).
Te ariā o te pH me te Whārite Pūmau Raina a Hofstadterawe
Ka taea te tatau i te uara pH o tētahi otinga parepare mā te whakamahi i te whārite Henderson-Hasselbalch:
\[ \text{pH} = \text{pK}_a + \log \left( \frac{[\text{Pūtake Hononga}]}{[\text{Waikawa]} }\right) \]
kāore i te mana:
– Ko te \(\text{pH}\) te nui o te waikawa o te wairewa.
– Ko te \(\text{pK}_a\) te pūmau wehenga waikawa o te waikawa i whakamahia.
– Ko te \([\text{Pūtake Honohono}]\) te kukū o te pūtake honohono.
– Ko te kukū o te waikawa ko \([\text{Acid}]\).
Ngā Wāhanga e Hiahiatia ana hei Hanga i tētahi Otinga Pūwero
1. Waikawa ngoikore/Pūtake ngoikore: Kōwhiria he waikawa ngoikore, he pūtake ngoikore rānei, he tata te pH ki te pH e hiahiatia ana.
2. Tote Waikawa/Turanga Honohono: Kōwhiria te tote waikawa hono, te tote turanga rānei e tika ana hei waihanga i te pūnaha ārai.
3. Otinga Paerewa: Ka āwhina te otinga paerewa ki te horoi, ki te whakau rānei i te pH o te pūwero.
Ngā Hipanga hei Hanga i tētahi Otinga Pūwero
1. Whakatauhia te pH e hiahiatia ana
Whakatauhia te pH e hiahiatia ana mō te pūwero. Hei tauira, ki te hiahia koe ki tētahi pūwero me te pH o te 7,0, ka taea e koe te whakamahi i te pūnaha ngā waikawa me ngā turanga ngoikore tōna hononga honohono e tata ana te (kuputuhi{pK}_a) ki tēnei uara.
2. Kōwhiria te Pūnaha Pūnaha Tika
Tīpakohia te takirua waikawa-pūtake hei whakamahi. Hei tauira, ko te waikawa acetic (\(\text{pK}_a = 4.76\)) me te konutai acetate e whakamahia ana mō te arai acetate, ko te haukini (\(\text{pK}_b\) mō te NH₃ he 4.75) me te ammonium chloride e whakamahia ana mō te arai haukini.
3. Tātaihia te Ōwehenga Ngā Waikawa me ngā Kawenga Hononga
Whakamahia te whārite Henderson-Hasselbalch hei tatau i te ōwehenga e hiahiatia ana o te waikawa ki te turanga honohono. Hei tauira, ki te hanga i tētahi arai me te pH o te 7 mā te whakamahi i te waikawa phosphoric (\(\text{pK}_a 2 = 7.2\)), ka pēnei te whārite:
\[ 7.0 = 7.2 + \log \left( \frac{[HPO_4^{2-}]}{[H_2PO_4^{-}]} \right) \]
Nō reira,
\[ \log \left( \frac{[HPO_4^{2-}]}{[H_2PO_4^{-}]} \right) = 7.0 – 7.2 \]
\[ \log \left( \frac{[HPO_4^{2-}]}{[H_2PO_4^{-}]} \right) = -0.2 \]
\[ \frac{[HPO_4^{2-}]}{[H_2PO_4^{-}]} = 10^{-0.2} \approx 0.63 \]
Nō reira, e 0.63 ngā mole o te turanga honohono (HPO_4^2-) e hiahiatia ana mō ia mole o te waikawa (H_2PO_4^-).
4. Whakaritea he Otinga Waikawa me te Pūtake Honohono
Kia rite ngā otinga rakau o ngā waikawa me ngā kawa honohono i roto i ngā kukū e mōhiotia ana. Hei tauira, ki te mea kei te hanga koe i tētahi otinga arai 1 rita, me tatau ngā otinga waikawa me te turanga i runga i te taahiraa o mua.
5. Whakaranua te Otinga
Whakaranua ngā otinga waikawa me ngā otinga kakano honohono ki ngā ōwehenga kua tatauhia. Hei whakarite i te pH tika, whakaohokia te ranunga kia tino pai, ka whakamātautau i te pH mā te whakamahi i tētahi mita pH kua whakatikatikaina.
6. Whakatikatikahia te pH mēnā e tika ana
Mena kāore te pH o te otinga parepare i te rite ki te hiahia, ka taea e koe te whakatika mā te tāpiri i ētahi iti o te waikawa kaha (hei tauira, HCl) me te turanga kaha rānei (hei tauira, NaOH) kia tae rā anō ki te pH e hiahiatia ana. Heoi anō, me tūpato kei kino te pūnaha parepare mā te tāpiri i te nui rawa o te waikawa, o te turanga rānei.
7. Whakapūmautanga Tūturu
Kia tika te pH, tāpirihia te wai whakakore ion ki te rōrahi e hiahiatia ana, hei tauira 1 rita mēnā kei te whakarite koe i te 1 rita o te pāhare pākawa waro.
Tauira Whaihua mō te Hanga Otinga Pūwero
Tauira 1: Pūwero Phosphate (pH 7,0)
Hei hanga i te 1 rita o te otinga pāhare pākawa me te pH 7,0:
– Ngā rauemi e hiahiatia ana:
– 0,1 M Na₂HPO₄ (Pūkawaihaite Hauwai Konutai)
– 0,1 M NaH₂PO₄ (Pūkawaihāte Dihydrogen Konutai)
– Ngā Hipanga:
1. Tātaihia te ōwehenga mā te whakamahi i te whārite Henderson-Hasselbalch e ai ki ngā mahi i runga ake nei.
2. Whakaranua te 0,63 mol (63 ml) Na₂HPO₄ ki te 1 mol (100 ml) NaH₂PO₄.
3. I muri i te whakaranu, whakamātauria te pH, ā, whakatikatikahia mēnā e tika ana.
4. Tāpirihia te wai kia tae rā anō ki te 1 rita te rahinga.
Tauira 2: Pūwero Āketita (pH 4.76)
Hei hanga i te 500 ml o te otinga parepare acetate me te pH 4.76:
– Ngā rauemi e hiahiatia ana:
– 0.1 M Waikawa Āketi (CH₃COOH)
– 0.1 M Konutai Āketita (CH₃COONa)
– Ngā Hipanga:
1. Whakaranua te 0.5 mol o te waikawa acetic ki te 0.5 mol o te konutai acetate.
2. Whakamātauria te pH, ā, whakatikatikahia mēnā e tika ana.
3. Tāpirihia te wai kia eke ki te 500 ml te rahinga.
Whakamutunga
Ko te hanga i ngā otinga pūmau me mārama ki te matū waikawa-pūtake me te kaha ki te mahi tātaitanga mā te whakamahi i te whārite Henderson-Hasselbalch. Mā ngā mahi pūnaha, ka taea e koe te hanga i ngā otinga pūmau ka pupuri i te pH pumau i raro i ngā momo āhuatanga whakamātautau. Mā te mahi tonu, ka matatau ake koe ki te hanga i ngā otinga pūmau e hāngai ana ki ō hiahia.
