1. If a student used an excess of HCI to dissolve 0.0565 grams of pure Mg ribbon

Question

1. If a student used an excess of HCI to dissolve 0.0565 grams of pure Mg ribbon. The temperature was 22.0 °C, the atmospheric pressure was 755 mmHg and the volume of hydrogen gas collected was 45.0 mL a) Using the mass of magnesium, how many grams of hydrogen (H2) gas could the student produce? 2 HCl (aq) + Mg MgCl2 (aq) + H2 (g) b) If the lab thermometer reads 22.0 °C, what is the vapor pressure of water in mmHg (look up this value in the table in the introduction)? c) What is the partial pressure of the H2 gas? PH2 PT PH20 d) Using the ideal gas law, PV-nRT, calculate the moles of hydrogen gas collected in the eudiometer. R = 0.0821 atm·Lmol.K and then convert it to grams of H2

Explanation / Answer

Q1

a)

mol of Mg = mass/MW = 0.0565/24.3 = 0.002325 mol of Mg

1 mol of Mg = 1 mol of H2

0.0023045 mol of Mg = 0.002325 mol of H2

mass = mol*MW = 0.002325 *2 = 0.00465

b)

Pvapor of water 22°C = 19.8 mm Hg ( From data)

c)

Pgas= Ptotal - Pvapor = 755-19.8 = 735.2 mm Hg

d)

PV = nRT

n= PV/(RT)

n = (735.2)(0.045)/(62.4*(22+273))

n = 0.00179 mol of H2

mass = mol*MW = 0.00179*2

mass of H2 = 0.00358 g

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