Number 2 and 3 What is the purpose of the graduated cylinder in the collection o

Question

Number 2 and 3

What is the purpose of the graduated cylinder in the collection of hydrogen gas by water displacement? What other type of laboratory glassware can fulfill this role? 2. 3. A 0.286-g sample of Zn was used to produce H2(g) by the reaction Zn(s) + 2HCI(aq)- ZnCl2(aq) + H2(g). The barometric pressure was recorded as 761.6 mm Hg and room temperature was 20°C. When the water levels of the eudiometer tube and graduated cylinder were equal, the volume of H2 was measured as 94.8 mL. Calculate the number of moles of hydrogen gas produced in the reaction Also, calculate the theoretical number of moles that can be obtained with the given amount of metal. (Assume the acid is in excess.) Finally, determine a error.

Explanation / Answer

2. The purpose of the graduated cylinder in the experiment is to tell about the volume of H2 collected by the water which is displaced. If we take a normal jar, then it is difficult to measure that volume. We can also take a beaker which has the labeling of the volume. It can also tell that how much water has been displaced.

3. In the experiment, pressure = P = 761.6 mm Hg = 761.6/760 = 1.002 atm

Temperature = 20 oC = 273+20 = 293 K

Volume = 94.8 ml = 0.0948 L

Gas constant = R = 0.082 L.atm/mol.K

Using ideal gas equation, PV = nRT

number of moles = n = PV/RT = 1.002*0.0948/(0.082*293) = 0.0040 mol

Number of moles of H2 collected = 0.004 mol

Theoretically,

In the reaction, mass of Zn used = 0.286 g

Molar mass of Zn = 65.4 g/mol

Moles of Zn used = mass/molar mass = 0.286/65.4 = 0.0044 mol

In reaction, 1 mol of Zn gave 1 mol of H2.

So, 0.0044 mol of Zn will give 0.0044 mol of H2.

Experimental yield = 0.0040 mol

Theoretical yield = 0.0044 mol

% error = [(theoretical-experimental)/theoretical]*100

= [(0.0044-0.0040)/0.0044]*100 = 9.09 %

% error = 9.09 %

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