CemistryTutorSite.com

The Molarity of Concentrated of H2SO4 (Sulfuric Acid)

Molarity of concentrated of sulfuric acid (H2SO4) can be calculate if the density of the solution and its percentage concentration are known. We usualy calculate the molarity of concentrated sulfuric acid when we will preapare the more dilute of H2SO4 solution. We do this more in the analytical experiments. But the easy way is to take a look on the label of the container of the concentrated sulfuric acid solution. From this we can get the density and the percent by mass of this solution. How we can calculate the molarity of concentrated H2SO4? just take the example below:

“Calculate the molarity of concentrated of H2SO4 (sulfuric acid solution) that has the spesific gravity 1.84?”

Here the answer:

First we should now the definition of specific gravity (SG). SG is  defined as the ratio of density of the material to the density of water at a specified temperature 4^oC. Specific Gravity is dimensionless and can be expressed as

SG = p / pH2O

where
p = density of the material
p = density of H2O at 4^oC= 1000 Kg/m³ = 1 g/cm³

from the formula above we can calculate the density of the concentrated of sulfuric acid solution as

density of concentrated H2SO4 solution
= SG x pH2O
= 1.84 x 1 g/cm³
= 1.84 g/cm³
= 1.84 g/mL

Assume that we have 100 mL of the concentrated of sulfuric acid thus we can calculate the mass of this solution

mass of solution
= volume x density
= 100 mL x 1.84 g/mL
= 184 g

mass of H2SO4 in this solution can be calculate by multipliying the mass of the solution with its concentration

mass H2SO4
= mass of the solution x percentage
= 184 g x 98%
= 180.32 g

and the moles of H2SO4 are
= mass / molar mass
= 180.32 g / 98.086
= 1.838 mol

and finaly the concentration of concentrated H2SO4 solution can be calculate by dividing the moles with the volume of the solution

Molarity H2SO4 concentrated = 1.838 mol / 0.1 L
Molarity H2SO4 concentrated = 18.38 M

Add comment June 12th, 2008

Calculate Molar Mass of A Gas Using Ideal Gas Law

Ideal gas law is an equation of state for a gas. This means that the state of the gas is its condition at a given time. It is important to recognize that the ideal gas law is an empirical equation that based on experimental measurements. The gas that obey this ideal gas law is said to behave ideally. However most gas obey the ideal gas law equation closely enough at pressure below 1 atm that only minimal errors result from assuming ideal behavior. A particular state of the gas is described by its pressure, volume, temperature, and number of moles. The knowledge of any three of these properties is enough to define the state of the gas, since the fourth property can be determined from the equation.

Here is the example how we calculate the molar mass of the gas using ideal gas law:

“What is the molecular mass of a gas if a volume of 500 cm³ has a mass of 1.00 g at -25⁰C and 98.4 KPa?”

use the ideal gas law formula

in which:
P = Pressure in atm
V = Volume in Liter
n = mol
R = universal gas constant 0.08206 L.atm/K.mol
T = Temperature in K

First change the unit of all of the formula above

1 atm = 101325 Pa , so
P = 98.4 KPa = 98400 Pa
P = 98400 Pa/101325 Pa x 1 atm = 0.971 atm
V = 500 cm3 = 500 mL = 0.5 L
T = (-25) + 273 = 248 K

and substitute to the ideal gas law we have

0.971 atm x 0.5 L = n x 0.08206 L.atm/K.mol x 248 K
n = 0.024 mol

we know that mol = mass / Mr , thus

Mr = mass/mol
Mr = 1 / 0.024
Mr = 41.667
Mr = 42

thus the molecular mass of the gas is 42 gr/mol

Add comment June 8th, 2008

The Ideal Gas Law Formula

The three laws of the behavior of the gas are discribe with the Boyle’s, Charles’s, and Avogadro’s law as mention below:

Boyle’s law (at constant T and n )

Charles’s law (at constant P and V)

Avogadro’s law ( at constant T and P)

The relationships in which the volume of the gas that depends on pressure, temperature, and the number of moles of gas can be write as:

the equation above can be writen as :

the equation above more familiar called “The Ideal Gas law”

P = pressure in atm
V = volume in Liter
n = number of moles in mol
R = universal gas constant = 0.08205 L.atm/K.mol

The ideal gas law can be used to solved a variety of problems. You can find one of the characteristic of the gas if the other three is known.

Add comment June 8th, 2008