(11 pts) 22. Hydrogen gas is produced when zinc reacts with sulfuric acid. If 15
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(11 pts) 22. Hydrogen gas is produced when zinc reacts with sulfuric acid. If 159 mL of wet hydrogen is collected over water at 24 C and a barometric pressure of 738 mmHg, how many grams of zinc have been consumed? The vapor pressure of water at 24°C is 22.4 mmHg. Zn(s) + H2SO4(l) H2(g) + ZnSO4(aq) (11 pts) 23. A 2.50 g sample of CaCl2 is added to 45.0 mL of water in a Styrofoam cup and stirred until it dissolves. The temperature of the solution increases from 22.7°C to 32.1°C. What is the heat of solution (AHson) of CaCl2? The specific heat of water is 4.184 J/(g.°C). Hsoln = ? CaCl 2(s) CaCl2(aq)Explanation / Answer
PV = nRT
V = 159ml = 0.159L
R = 0.0821L-atm/mole-K
T = 24+273 = 297K
PH2 = barometric pressure - vapor pressure of water
= 738-22.4 = 715.6mmHg
PH2 = 715.6/760 = 0.94atm
n = PVRT
= 0.94*0.159/0.0821*297 = 0.00612 moles
Zn(s) + H2So4 (aq) -----------> H2(g) + ZnSo4(aq)
1 mole of H2 produced from 1 mole of Zn
0.00612 moles of H2 produced from 0.00612 moles of Zn
mass of Zn = no of moles * gram atomic mass
= 0.00612*65.4 = 0.4g of Zn
23. mass of water = volume * density
= 45*1 = 45g
mass of solution = mass of CaCl2 + mass of H2O
= 2.5 +45 = 47.5g
DH = mCDT
= 47.5*4.184*(32.1-22.7)
= 1868.16J = 1.868Kj
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