6) Consider the diagram given below: Eudiomet H(B 2 HC1(aq) Zn (s) 21.8 cm water

Question

6) Consider the diagram given below: Eudiomet H(B 2 HC1(aq) Zn (s) 21.8 cm water 7.10 ml of 6.0 M HCl are added to 0.186 g 2n(s) in a tost tube. a) Write a balanced equation for the reaction taking place. b) The liberated H2 ) is collected by displacing vater from an eudiometer, a graduated glass measuring tube for gas analysis. After the reaction is complete, the volume of H2(g) collected above water is 72.18 ml at 18.8. The height of water column in the eudiometer is 21.8 om and the atmospheric pressure ia 753.2 mm Hg,"At 18.8°C the density of Hg is 13.6 g/cms and the water vapor pressure is 17.54 torr. Calculate the ideal gas constant, R, from the information given. Setup:

Explanation / Answer

a)

Reaction is acid + zinc

Zn(s) + 2HCl(aq) = H2(g) + ZnCl2(aq)

b)

V-H2 = 72.18 mL

T = 18.8°C --> 291.8 K

height = 21.8 cm of water

PAtm = 753.2 mm Hg

Get R from this info:

PV = nRT

R = PV/(nT)

moles of H2 --> from ratio

mol of Zn = mass/MW = 0.186/65.39 = 0.002844

mol of HCl = MV = 6*7.1*10^-3 = 0.0426

ratio is 1:2 so , HCl i slimiting, then

0.0426 mol of HCl = 1/2*0.0426 = 0.0213 mol of H2

n = 0.0213

T =291.8

V = 72.18 mL = 72.18*10^-3 L

now, we need P, which is much more complex

From pressure balance:

Ptotal = Pgas + Pwater

753.2 mm Hg = Pgas +

Pgas = 753.2-17.54 = 735.66 mm Hg

R = PV/(nT) = (735.66)(72.18*10^-3)/(0.0213*291.8 )

R = 8.543 mm Hg - L / mol K

now...

c)

%error

Error = (real - calcualted)/real * 100 %= (62.4-8.543)/(62.4)*100% = 86.30% error

d)

H2 via

V molar = V/mol = 72.18 / 0.0213 = 3388.7 mL/mol = 3.3 L/mol

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