Question

Determine the mass (in grams) of magnesium metal required to produce 40.0 mL of H2 with a temperature of 26.9 oC and an atmospheric pressure of 745 mmHg. Be sure to take into account water vapour.

3. A sample of a halogen gas has a mass of 0.538 g and exerts a pressure of 600.0 torr at 14.0 oC in a 100.0 mL flask. Calculate the molar mass of the halogen gas. Is the halogen gas F2, Cl2, Br2 or I2? R = 0.0821 L atm/mole K 1 atm = 760 torr

Answer 1

Determine the mass (in grams) of magnesium metal required to produce 40.0 mL of H2 with a temperature of 26.9 oC and an atmospheric pressure of 745 mmHg. Be sure to take into account water vapour.

The reaction between Mg and HCl is as follows:

Mg+ 2HCl -- > MgCl2 + H2

First calculate the moles of H2 as follows:

Here the total pressure = 745 mmHg So the pressure of the hydrogen is really 745 -27 mm Hg of Water vapor

= 718 mmHg or 0.945 atm

Volume = 40.0 ml = 0.040 L and R = 0.0821 L atm / K.mol, T= 26.9 Oc or 300.05 K

PV= n RT

n = PV/RT

n= 0.945 *0.040/ 0.0821* 300.05

n=1.53*10^-3 mol

Now calculate the moles of Mg:

1.53*10^-3 mol H2 * 1 mol Mg/ 1 mol H2

= 1.53*10^-3 mol Mg

Amount of Mg= moles * molar mass

= 1.53*10^-3 mol Mg*24.305 g/ mol

= 0.037 g Mg

3. A sample of a halogen gas has a mass of 0.538 g and exerts a pressure of 600.0 torr at 14.0 oC in a 100.0 mL flask. Calculate the molar mass of the halogen gas. Is the halogen gas F2, Cl2, Br2 or I2? R = 0.0821 L atm/mole K 1 atm = 760 torr

Volume = 100.0 ml = 0.100 L and R = 0.0821 L atm / K.mol, T= 14.0 Oc or 287 K

And P = 600 torr = 0.789 atm

PV= n RT

n = PV/RT

n= 0.789 *0.100/ 0.0821*287

n= 3.4*10^-3 mol

number of moles = amount in g/ molar mass

molar mass = amount in g/ number of moles

molar mass = 0.538 g/ 3.4*10^-3 mol

= 158.2 g/ mol

The molar mass of Br is Molar mass of Br2 is 159.8 thus the helogen is Br.