1)Small quantities of H 2 gas can be collected by adding HCl to Zn. A sample of
ID: 856190 • Letter: 1
Question
1)Small quantities of H2 gas can be collected by adding HCl to Zn. A sample of 195 mL of H2 gas was collected OVER WATER at 25 C and 753 mm of Hg. What mass of H2 was collected? (vp of water at 25 C is 24 mm of Hg)
a) 0.00765 g b) 0.0153 g c) 0.0159 g d) 0.0164 g e) 11.7 g
2)How many molecules of O2 occupy a volume of 1.0 L at 65 C and 778 mm of Hg?
a) 0.037 molecules? b) 2.2 x 1022 molecules ? c) 1.2 x 1023 molecules d) 1.7 x 1025 molecules
3)If the pressure of a gas is tripled and the absolute temperature of the gas is quadrupled, by what factor will
a) H2 b) O2 c) N2 d) Cl2 e) all the same
the volume of the gas change?
Explanation / Answer
1. Zn+ 2HCl - -> ZnCl2 + H2(g))
pH2 = Ptotal -Po2 = 753 - 24 = 729 mmhg
no of moles of H2 = 0.9592*0.195/0.0821*298.15
= 0.00764 mole
mass of H2 = 0.0153 grams.
B is correct answer.
2.
volume at STP = 760*273.15/778*338.15* 1
= 0.789 lit
at stp
22.4 l = 6.023*10^23 molecules
0.789 lit = ?
no of molecules of H2 = 6.023*10^23*0.789/22.4 = 2.1214942*10^22 molecules.
B is correct answer.
3. p2 = 3p1
t2 = 4t1
P1V1/T1 = P2V2/T2
P1V1/T1 = 3P1*V2/4T1
V2 = V1*4/3 = 1.33 V1
Then volume of H2,o2,n2,cl2 is increased to 4/3 times of it original volume.
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