Kimyo bakalavr) 2021-2022 o’quv yili I semester uchun II kurs (III semestr) namangan – 2021

Lаbоrаtоriya ishi-12

Eritmаdаgi sulfаt iоnlаri miqdоrini аniqlаsh
Usul sulfat ionining bariy ioni bilan kam eriydigan (K_s°= 1,1 ^. 10^-10) mayda kristall cho'kma hosil qilishiga asoslangan:

SO₄^2- + Ba²⁺  BaSO₄ .

BaSO₄ cho'kmasi mayda kristall tuzilishli bo'lganligi uchun hosil bo'ladigan cho'kmaning mumkin qadar yirikroq bo'lishi uchun sharoit yaratishga e'tibor berish kerak. Hosil qilingan cho'kma dekantatsiya qilinib yuviladi, filtrlanadi, filtr ustida yana yuvib, adsorbilangan begona moddalar qoldiqlaridan tozalanadi. Filtr bilan cho'kma yuvilgandan so'ng quritiladi va kuydiriladi. Kuydirilgan qoldiq bo'yicha tekshiriladigan modda tarkibidagi sulfatning miqdori aniqlanadi.

Sulfatni aniqlashda cho'ktiriladigan va tortiladigan shakllar bir xil bo'lib, cho'kmani kuydirish vaqtida analizga qator xalaqit beruvchi jarayonlar sodir bo'lishi mumkin. Bular qatoriga filtrni kuydirishda hosil bo'lgan kо'miming cho'kmani qisman qaytarishi

BaSO₄+2C BaS+2CO₂

natijada hosil bo'lgan sulfidning havo kislorodi ta'siridan oksidlanib, BaSO₄ hosil qilishi

BaS+2O₂BaSO₄

qizdirish juda katta haroratda o'tkazilayotgan bo'lsa, BaSO₄ cho'kmasining parchalanishi

BaSO₄BaO+SO₃

kiritilishi mumkin. Bundayjarayonlar analizga tegishli xato kiritadi. Ayrim hollarda xatoning oldini olish maqsadida mazkur reaksiyalar davomida hosil bo'lgan BaS va BaO moddalarini sulfatga aylantirish uchun qoldiq 2-3 tomchi konsentrlangan sulfat kislota eritmasi bilan ishlanadi:

BaS + H₂SO₄ BaSO₄ + H₂S

va BaO + H₂SO₄  BaSO₄ + H₂O

So'ngra asta-sekin mo'rili shkafda ortiqcha kislota parchalanib ketgunga qadar qizdiriladi h₂so₄  h₂o + so₃

Shuni unutmaslik kerakki, bunday amal analizga xato kiritishi ham mumkin. Shu bois undan juda ehtiyotkorlik qilingan kam hollardagina foydalanish mumkin.

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