Bonjour,
Ex 8
1) pipette jaugée
2) F = C/C' = V'/V = 500/25 = 20
3) n = C x V = 3,2.10⁻² x 25,0.10⁻³ = 8,0.10⁻⁴ mol
4) ⇒ C' = n/V' = 8,0.10⁻⁴/500.10⁻³ = 1,6.10⁻³ mol.L⁻¹
(on retrouve F = C/C' = 3,2.10⁻²/1,6.10⁻³ = 20)
5) n' = C' x V" avec V" = 20 mL
soit n' = 1,6.10⁻³ x 20.10⁻³ = 3,2.10⁻⁵ mol
Ex 4
V' = 200.10⁻³ L et C' = 5,0.10⁻¹ mol.L⁻¹
Cm = 184 g.L⁻¹
1) M(NH₃) = M(N) + 3xM(H) = 14 + 3x1,0 = 17 g.mol⁻¹
C = n/V = (m/M)/V = m/V x 1/M = Cm/M
soit C = 184/17 ≈ 11 mol.L⁻¹
2) n = C x V = C' x V'
⇒ V = V' x C'/C
soit V = 200.10⁻³ x 5,0.10⁻¹/11 ≈ 9,2.10⁻³ L soit 9,2 mL
