1. What mass of pure sulfuric acid (molar mass = 98.09 g/mol) is needed to produ
ID: 507844 • Letter: 1
Question
1. What mass of pure sulfuric acid (molar mass = 98.09 g/mol) is needed to produce 1L of aqueous sulfuric acid solution with pH=2?
2. Using standard bond enthalpies, predict whether 2CO2 --> CO + O2 is endo- or exothermic, and give the H°rxn
3. A hydrate of FeSO4 loses 45.3% of its mass when heated, changing from blue-green to tan. What is the formula of the hydrate (FeSO4 * xH2O)? (solve for x)
4. Heating a sample of liquid has what effect on enthalpy and entropy? (increase or decrease in H and S)
5. Are you concerned with the heat death of the universe? Why or why not?
Explanation / Answer
1) pH = 2 that is [H+] = 1.0x10-2 M
thus to prepare 1.0x10-2 M sulfuric acid ,
molarity = (mass/molar mass) /V (L)
1.0x10-2 M = (xg/98.09g/mol)/1 L
thus x g = 0.9809 g
2) 2CO2 ----------> CO + O2
delta H rxn = bond enthlpies of reactants - products
= [4xC=O] - [1xCtriple O + 1xO=O]
=[4x799] -[1072 +494]
= + 1630 kJ
Thus the reaction is endothermic.
3) FeSO4 water
%mass 54.7 45.3
moles 54.7/151.908 45.3/18
= 0.36 =2.516
ratio 1 6.99
Thus the ratio of FeSo4 to water is 1:7 or for one mole of FESO4 , 7 water molecules are present.
Thus the formmula is FeSO4 .7H2O
4) X(l ) <-------> X9G)
The entropy of a substance increases with temperature and varies with physical state as
S solid < S liquid < S gas.
Thus heating a sample of liquid increase the entropy.
Similarly delta H , enthalpy also increases with temeperature.
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