Bonjour,
Ex 1)
1) M = 12xM(C) + 22xM(H) + 11xM(O) = 12x12 + 22x1 + 11x16 = 342 g.mol⁻¹
2) n = m/M = 6/342 ≈ 1,75.10⁻² mol
3) N = n x Na = 1,75.10⁻² x 6,02.10²³ ≈ 1,05.10²² molécules
Ex 2)
1) M = ... = 194 g.mol⁻¹
2) n = m/M = 80,0.10⁻³/194 ≈ 4,12.10⁻⁴ mol
3) 600/80 = 7,5 donc 7 tasses
4) Masse café = 250 g
⇒ masse caféine : m = 250 x 0,10% = 0,25 g
⇒ n = m/M = 0,25/194 ≈ 1,29.10⁻³ g
Ex 3)
1) M = ...
2) n = C x V ...
3) m = n x M = C x V x M
4) C = n/V = (m/M)/V = m/MV
Ex 4)
1) car la digestion et l'effort physique augmente la concentration en acide lactique du sang.
2) M = ... = 90 g.mol⁻¹
C = 0,55 mmol.L⁻¹
⇒ Cm = C x M = 0,55.10⁻³ x 90 = 49,5.10⁻³ g soit environ 50 mg
C = 2,2 mmol.L¹
⇒ Cm = C x M = 2,2.10⁻³ x 90 = 198.10⁻³ g donc environ 200 mg
