You multiply the molarity by the volume in litres.
Explanation:
Molarity is the number of moles of a substance in one litre of solution. The official symbol for molarity is “c” (concentration), but many people use the old symbol “M”.
M
=
n
V
, where
n
is the number of moles and
V
is the volume in litres.
We can rearrange this equation to get the number of moles:
n
=
M
×
V
Example
:
How many moles of
NaCl
are contained in 0.300 L of 0.400 mol/L
NaCl
solution?
Solution:
n
=
0.300
L soln
×
0.400 mol NaCl
1
L soln
=
0.120 mol NaCl
Answer:
n = 2.208x10¹⁸ photons
Explanation:
The energy of a photon( an elementary particle) is given by the equation:
E = nxhxf
Where n is the number of photons, h is plank constant (6,62x10⁻³⁴ J.s), and f is the frequency. Knowing that the power level is 0.120mW (1.2x10⁻⁴ W), the energy in J, for a time of 78 min (4680 s)
E = 1.2x10⁻⁴x4680 = 0.5616 J
The frequency of a photon is its velocity ( c= 3x10⁸ m/s) divided by its wavelength, which is 780 nm = 780x10⁻⁹ m
f = 3x10⁸/780x10⁻⁹
f = 3.846x10¹⁴ s⁻¹
Then, the number of photons is:
0.5616 = nx6,62x10⁻³⁴x3.846x10¹⁴
n = 2.208x10¹⁸ photons.
Answer: The heat energy produced is 53831.25KJ
Explanation:
METHANE is the main component of natural gas. It can undergo combustion reaction in air with a bright blue flame to produce carbondioxide and water. The heat of reaction (enthalpy) is negative because heat is absorbed during the chemical reaction. To calculate the heat energy produced by the combustion of one kilogram (1 kg) of methane the following steps are taken:
Molecular mass of methane =16 gm/mol.
So moles of 1 kg methane =
Given mass of methane ÷ molecular weight of methane
But the given mass = 1kg = 1000g
Therefore,
moles of 1000g methane = 1000÷16
= 62.5 moles
Hence, energy evolved = (moles of methane) × (heat of combustion)
Therefore,
heat energy produced= 62.5 × (-861.3kj)
= -53831.25kj
1) moles = mass/mR
CaCO3 Mr = 40 + 12 + (16×3)
= 52 + 48
= 100
mass = 15
so the moles would be 15 ÷ 100
which is 0.15 moles of CaCO3
2) moles = mass ÷ Mr
Mr of Al2O3 = 27 + (16×3)
= 27 + 48
= 75
mass = 204
so the moles would be 204/75 which is 2.72 moles of Al2O3
