I can't do this kinetic energy question. I've got the mark scheme but I still don't get it. Please help!?

2019-02-19 6:33 pm

(d) Calculate the mass, in kg, of a single 25Mg+ ion.
Assume that the mass of a 25Mg+ ions is the same as that of a 25Mg atom.
(The Avogadro constant L = 6.022 × 1023 mol–1) ...................................................................................................................................... .................................................................................................................................. [1]
(e) In a TOF mass spectrometer, the kinetic energy (KE) of a 25Mg+ ion was 4.52 × 10–16J Calculate the velocity of the ion using the equation.
KE = 1⁄2 mv2 (m = mass / kg and v = velocity / ms–1

更新1:

the mark scheme answer to (d) = 1.5055 x10^22 answer to (e) = 1.48 × 10⁻⁵ m s⁻¹

更新2:

copied (e) wrong sorry its answer to (e) = 1.48 × 10⁵ m s⁻¹

回答 (1)

胡雪8°

2019-02-19 7:14 pm

(d)
Mass of 1 mole of ²⁵Mg⁺ ions = 25.0 g mol⁻¹
Mass of a single ²⁵Mg⁺ ion = (25.0 g mol⁻¹) / (6.022 × 10²³ mol⁻¹) = 4.15 × 10⁻²³ g

(e)
K.E. = (1/2) m v²
4.52 × 10⁻¹⁶ J = (1/2) × (4.15 × 10⁻²³ / 1000 kg) × v²
Velocity, v = √[4.52 × 10⁻¹⁶ × 2 × 1000 / (4.15 × 10⁻²³)] m s⁻¹ = 1.48 × 10⁻⁵ m s⁻¹

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