Results after the experiment
Amount of magnesium used (g) = 0.0590
Volume of h20+hcl in eudiometer= 63 cm3
Volume of h2 gas formed= 58.8 cm3
Pressure of room= 104.2 kpa
Water vapor pressure at 22c= 2.6kpa
Temperature of the room= 22 c
Discussion and conclusion.
Step one: - The Dalton’s law of particle pressure states that the total pressure of a mixtures of gases is equal to the sum of the pressure of all of the constituent gases alone. For this experiment, the total pressure inside the eudiometer will be the sum of the pressure of the hydrogen gas formed and the water vapor. It can be expressed as follows:
P eudiometer = Ph2+ P water vapor …………………………………………….Equation 1
Here the total pressure of the eudiometer is equal to the pressure of the room since it was lifted making its water level equal to the level of water in the measuring cylinder. The pressure of water vapor at 22c is equal to 2.6Kpa (refer to table 1). Then the pressure of hydrogen gas is:
P h2= P Eudiometer – P water vapor
= 104.2 Kpa – 2.6 Kpa
= 101.6 Kpa
Step two:- An ideal gas is one in which there are no attractive forces between the particles and the kinetic energy of the particles is directly proportional to the absolute temperature. In an ideal gas equation, the pressure and volume of the gas are related to the amount and temperature of the gas by ideal equation:
P*V=n*R*T …where P is pressure in Kpa
V is volume in dm3
N is in moles ………………………………………..................Equation 2
T is temperature in Kelvin
R is ideal gas constant with value of 8.314 k-1mol-1
From the above equation, we can derive that the amount of substance (n) is equal to
n = P*V ..........................................................................Equation 3
R*T
By applying equation 3, it is possible to find out the amount of substance (n) for the hydrogen gas formed:
n = 101.6 Kpa * 0.0588 dm3
8.314 k-1 mol-1 *295 k
= 0.0024 moles of hydrogen gas
From the balanced chemical equation we can find out that for every mole of magnesium used there will be one mole of hydrogen gas formed. So for 0.0024 moles of hydrogen gas formed, 0.0024 moles of magnesium must have been used.
Mg(s) + 2HCl→ h2(g) + mgcl2(aq)
One mole excess one mole
The molar mass of magnesium can be found using the following formula:
Molar mass (M) = given mass (m) …………………………………Equation 4
Amount of substance (n)
Then…. Molar mass of magnesium = 0.0590 g
0.0024 moles
= 24.2 ≈ 24
The percentage yield of the reaction can be calculated using the following formula:
% yield = Actual yield × 100 ………………………………………………Equation 5
Theoretical yield
Theoretical yield: - is calculated amount (or expected yield) of a product when a limiting reactant is completely consumed. In this reaction, the limiting reactant is magnesium.
Mg(S)+2 HCl → H2(g)+mgcl2(aq)
24 g 2 g …….where 24 and 2 are molar masses of mg and h2
0.0509 g X
Then X is equal to = 2 g × 0.0509g = 0.0042 g of hydrogen gas
24 g
This can be written in terms of amount of substance (n) for hydrogen gas:
Amount of substance (n) = 0.0042 g
1 g
= 0.0042 moles of hydrogen gas
Actual yield: - is the amount of product actually obtained i.e. the quantity of product finally collected or isolated from a reaction. In this case, the actual amount of hydrogen gas obtained is 0.0024 moles. Then by applying equation 5 the percentage yield can be found.
% yield = Actual yield × 100
Theoretical yield
= 0.0024 × 100
0.0042
= 57.1%
Usually actual yield is less than theoretical yield for many reasons. It could be problem with the apparatus used and errors in measurement etc.