m,,„, .100% .
C2% = 92,23% = — ^ (2)
^ 10.1,8+IS.HH,,,
V i d binh 1 nudrc bi háp thu bai dung dich H2SO4 dac, do do n6ng do axit CO giam nhung m„ s,,^ khdng d6i ntn chia (1) cho (2) ta c6:
18+18n„,„ 95
n„,„=0,03 mol.
18 92.32 . => m„ = 2. n„ o = 0,06 gam. . => m„ = 2. n„ o = 0,06 gam. • Do tang kh6'i luong binh 2 bang m^o, •
3 3.1,32 , =^ m,, =—.m„,^ = — j y - - = 0,36 (gam). =^ m,, =—.m„,^ = — j y - - = 0,36 (gam).
=> mo = 0,74 - (0,06 + 0,36) = 0,32 (gam).
Goi c6ng thiic ciia X la C.HyO,
0,36 0,32 „ , -
=> X : y : z = : 0,06 : = 3 : 6 : 2 ^ 12 16 => C6ng thiJc dom gian nhát cua X: CiH^Oj. CO CTPT ciia X ta tinh Mx:
MA = 2.37 = 74 g/mol.
=>(C3H,02)„ = 7 4 : ^ n = 1.
CTPT ciia X chinh la cAng thiic dcm gian nhát: QH^Oj.
b) Bien luan xdc dinh cong thiic phan tA
Mot bai toan xac dinh CTPT hop chat hiJu ca duoc coi la dii di6u kidn khi dong thcri cho biét:
- Khoi lugng mol cua chat hiJu cọ
- Kh6'i lugng cac san ph^m phan tich (d6't chay) d^ xac dinh c6ng thiJc don gian nhát (CTDGN).
Neu thieu m6t trong 2 di^u kien tr^n thi bai toan can dugc giai bang
phuong phap bien luqn thfch hop.
- Bien ludn khi chi biet khoi liMnfi mol (M^)
\2\ y = M^
M
12x < M ^ X < n
Ket hop v6i dieu kifin y < 2x + 2 va cac gia trj x, y nguyfin duong (y chi láy gia tri chSn) => lap bang xet gia tri cua y theo x, tim cap nghiSm thfch hgp.
D6'i vdri hidrocacbon khi: x < 4.
+ Neu A CO chiia oxi (C,HyOJ, ta co phuong trinh: 12x + y + 16z = MA
I 1 2X < M A; 1 6Z < M A
y chan va y < 2x + 2
Cho z = 1 tinh X, y tuong tu tru&ng hgp trfin.
12x + y = M A- 1 6 .
Cho z = 2 12x + y = M A - 32
Gia trj cua z phu thu6c vao hgp chat huu co chiia cac nhom chiic khac nhau: ancol, etc, andehit, xeton, axit, estẹ.. va kh6'i lugng mol.
+ Dua vao c6ng thiic tinh s6' liSn ket d6i (hoac s6' vong) hoac lien k€t
ba (mot lien két ba bang 2 lien két doi) trong phan tir de xac djnh CTCT
(đng phan) co thi co, sau do dua vao tinh chat hoa hgc cua hgp chát hoac
cáu tao ciia san phdm phan ling oxi hoa kh6ng hoan toan hgp chat do d^
suy ra CTCT diing trong s6' cac d6ng phan da tim dugc.
- Bien luan khi chi biet CTDGN
+ Khi da tim dugc c6ng thiic don gian nhát (CIBGN), co th^ xac djnh CTPT |Jii biet hgp chat thu6c chiic nao (ancol, ete, andehit, xeton, axit, este, amin...).
+ Chuyen cAng thiic nguyfin thanh c6ng thiic chiia nhom chiic c^n xac djnh.
Thi du 1. CTDGN ciia axit huu c a no, da chiic la C2H3O2.
CTPT la (CH.Ô)^ -> C2„H,„02„.
Chuyen thanh CTPT cua axit: C„H2„(COOH)„.
Bien luan 6i tim gia trj ciia n dua vao s6' nguySn tir oxị
Thi du 2. Hay bien luan xac dinh CTPT cua m6t axit hflu c a no, mach
CO CTDGN la C2H3O2.
Viet CTCT ciia axit va ggi ten. Biét axit nay mach thang.
Hu&ng đn gidi:
Ggi CTPT cua axit la (C2H302)„ hay C2„H,„02„. -> C„H2„(COOH)„. V i axit no nSn:
2n = 2.n + 2 - n
=^n = 2 ^ C T P T : C4H,04
A x i t m a c h h d , thSng c6 C T C T : H G O C - C H ^ - CH^ - C O O H . 2. Xac d m h c o n g thiirc cau tao (CTCT) hdp chat hOru c a
- T u o n g ling vdri mftt C T P T c6 n h i ^ u C T C T (cac d 6 n g phan). Di xac
d i n h diing C T C T ciia m6l hap chat hQu ca phdi hiét mot so tinh chat hoci
hoc hoac mot so tinh chat vat li (nhir t " , t;;,,, d6 hoa tan...) ciia chát áỵ
- Cung CO the dua v a o cau tao san pham o x i hoa k h d n g hoan toan ciia hop chat hixu C O do ma s u y ra C T C T diing ciia nọ