<h3>Answer:</h3>
a) Moles of Caffeine = 1.0 × 10⁻⁴ mol
b) Moles of Ethanol = 4.5 × 10⁻³ mol
<h3>Solution:</h3>
Data Given:
Mass of Caffeine = 20 mg = 0.02 g
M.Mass of Caffeine = 194.19 g.mol⁻¹
Molecules of Ethanol = 2.72 × 10²¹
Calculate Moles of Caffeine as,
Moles = Mass ÷ M.Mass
Putting values,
Moles = 0.02 g ÷ 194.19 g.mol⁻¹
Moles = 1.0 × 10⁻⁴ mol
Calculate Moles of Ethanol as,
As we know one mole of any substance contains 6.022 × 10²³ particles (atoms, ions, molecules or formula units). This number is also called as Avogadro's Number.
The relation between Moles, Number of Particles and Avogadro's Number is given as,
Number of Moles = Number of Molecules ÷ 6.022 × 10²³
Putting values,
Number of Moles = 2.72 × 10²¹ Molecules ÷ 6.022 × 10²³
Number of Moles = 4.5 × 10⁻³ Moles
Ends....................?
I believe it’s A..but I’m not quite sure.
The atomic mass of K is 39
from Avogadro's law
39g of K contains 6.02x10^23 atoms
therefore if
39=6.02x19^23
X=5.11×10^22
making X the subject of the formula
X= (5.11×10^22×39)÷6.02×10^23
X= 33g
Answer:
20.468 kilo Joules is the enthalpy change when one mole of sodium nitrate dissolves.
Explanation:
Heat lost by solution ad calorimeter = Q
Heat capacity of solution ad calorimeter = C = 1071 J/°C
Change in temperature = ΔT = 21.56°C - 25.00°C = -3.44°C
Heat gained by sodium nitrate = -Q = -(-3,684.24 J)=3,684.24 J
Moles of sodium nitrate = 
When 0.18 mole of sodium nitrate was dissolved in water 3,684.24 joulesof heat was absorbed by it.
Then heat absorbed by 1 mole of sodium nitrate :
1 J = 0.001 kJ
20.468 kilo Joules is the enthalpy change when one mole of sodium nitrate dissolves.
