Analitik kimyoda organik reagentlar

Suvning ion ko‘paytmasi, suvli eritmalarning pH qiymati
Suv o‘ta kuchsiz elektrolit H₂O = H⁺ + OH^–
MTQ ni qo‘llassak:
(I)
(I) tenglama suvning dissotsiatsiyalanish darajasi. [H₂O] - suv molekulasining dissotsiatsiyalanmagan molyar konsentratsiyasi bo‘lib, 1 litr suvdagi mollar sonidir.

Distilangan suvdagi [H⁺] va [OH^–] ionlari konsentratsiyalarini ko‘paytmasi IK_H2O = [H⁺] * [OH^–] suvning ion ko‘paytmasi deb ataladi, uning qiytmati K_dis (H₂O) dan albatta farq etadi
[H⁺] * [OH^–] = K_H2O * [H₂O] =1,810^-16 * 55,56 = 1*10^-14
Demak suvning ion ko‘paytmasi doimiy son bo‘lib 1*10^-14 ga teng. Bu tenglikdan analitik reaksiyalar uchun o‘ta muxim bo‘lgan eritmaning pH qiymatini xisoblashda foydalaniladi.
Distillangan suvda [H⁺] = [OH^–] bo‘lgani uchun [H⁺]² = 1*10^-14
[H⁺] = √1*10^-14 = 1*10^-7 muxit neytral
Suvning ion ko‘paytmasini logariflab, barcha xadlarni (–1)ga ko‘paytirib:
(–1) · lg[H⁺] + lg[OH^–] = –14 · (–1); –lg[H⁺] + (–lg[OH^–]) = 14
Vodorod ioni konsentratsiyasini manfiy logarifmi rN deb ataladi

–lg[Н⁺] = рН

Demak suvning ion ko‘paytmasining logarifmik ko‘rinishi

pOH + pOH = 14
Suvli eritmalar pH qiymatlari quyidagi shkalada tavsiflanadi (3-rasm).

[H⁺]= 10^-1 10^-3 10^-5 10^-7 10^-8 10^-10 10^-12 10^-14

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pH= | 3 | | 5 | 7 | 8 10 | 12 14
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