Is the Chem B Final exam question?
Answer:
Molecular mass
Explanation:
Molecular formulas is the actual number of atoms of each element in the compound while empirical formulas is the simplest or reduced ratio of the elements in the compound.
Thus,
Molecular mass = n × Empirical mass
Where, n is any positive number from 1, 2, 3...
Thus if the molecular mass is known, then we can find the value of n which results to molecular formula.
Explanation:
The given data is as follows.
= 5.00 L, = ?
= -50.0 + 273 = 223 K, = 100.0 + 273 = 373 K
P = constant
Therefore, calculate as follows.
=
Since pressure is constant so, P will be cancelled out from both the sides.
=
=
=
=
= 8.36 L
Thus, we can conclude that is 8.36 L.
Answer:
16.5 g
Explanation:
When a nonvolatile compound is dissolved in a pure solvent, the freezing point of the solvent is reduced, because the interaction solvent-solute requires more energy to be joined, and so, it freezes. This property is called cryoscopy, and the temperature change (ΔT) can be calculated by:
ΔT = Kc*W*i
Where Kc is the cryoscopy constant of the solute X, W is the molality of the solution, and i is the van't Hoff factor, which determines the percent of the solute that is dissolved. For organic molecules, such as alanine, i = 1.
The molality is the number of moles of the solute divided by the mass (in kg) of the solvent (1200 g = 1.2 kg). The molar mass of alanine is 89.09 g/mol, and the number of moles of it is the mass divided by the molar mass:
n = 45.8/89.09
n = 0.5141 mol
W = 0.5141/1.2 = 0.4284 mol/kg
So, Kc of X is:
4.10 = Kc*0.4284*1
Kc = 9.57 °C.kg/mol
So, if now sodium chloride is added to X, and the variation temperature is the same, and i = 1.82:
4.10 = 9.57*W*1.82
W = 0.2354 mol/kg
The number of moles of the solute is then:
W = n/1.2
0.2354 = n/1.2
n = 0.2825 mol
The molar mass of sodium chloride is 58.44 g/mol, thus the mass is the molar mass multiplied by the number of moles:
m = 58.44*0.2825
m = 16.5 g
Answer:
Explanation:
aCa + bCO₂ + cO₂ → dCaCO₃
Chemical reactions obey the law of conservation of matter. The law states that "matter is neither created nor destroyed in the course of a chemical reaction". From this, we can deduce that the total mass of the products and reactants are equal.
To balance a chemical reaction, we can do so by inspecting the atoms/compounds involved and putting the appropriate coefficients at the back of the reactants and products. For equations in which inspection might not easily work, we can use a mathematical approach.
By inspecting the reaction above, we can easily balance it
Using the mathematical approach:
The coefficients are a,b,c and d. They are needed to conserve the atoms. So:
For Conservation of Ca: a = d (i)
C: b = d (ii)
O: 2b + 2c = 3d (iii)
if we assume that a = 1, then d = 1
b = 1
from (iii): 2c = 3d -2b
2c = 3- (2 X 1)
2c = 1
c =
Therefore we have a = 1
c =
b = 1
d = 1
aCa + bCO₂ + cO₂ → dCaCO₃
Ca + CO₂ + O₂ → CaCO₃