Lose Star CHEN 141 Exam 2 Fall 201 S A dlute solutioe is prepared by tmasferring

Question

Lose Star CHEN 141 Exam 2 Fall 201 S A dlute solutioe is prepared by tmasferring 30.00 mL of a 0-6274 Msck solution to 25.0 volumeteric flask A) 002s96 M and diluting to mark What is the molarity of this dilute solution? 0.3137 0.006490 MM D) 005192 E 0.1516M imienne of helium and chlorine, occupyin avolume of 23.3 L at 7446 Hg and 21.PC, it thar the partial pressure of chlorine ins 357 mmlg. What is the total mass of the sample A) 197 g B) 34.2 g C 70.9s D) 32.2 p E) 182g Using the van der Waals equation, determine the pressure of 352.0 g of So () in a 5.30-L at 751 K. For SO,(e), 6.865 L atm/moF and & 0.05679 L/mol A) 63.9 a B) 10.4 atm C) 75.3 atm D) 60.5 at E) 10.5 atm 8. Using the following data, calculate the standand enthalpy of reaction for the coal gasification A) +153 kJ B) -378.6kJ C) 378.6 kJ D) -157.2 k E) -116.0kJ 9, An unknown gaseous hydrocarbon consists of 85.63% carbon by mass. A 0.504-g sample of the gas occupies a volume of 0.268 L at STP. What is the identity of the gas? A) CaHs C) CH E CH

Explanation / Answer

Q5

We need to apply dilution law, which is based on the mass conservation principle

initial mass = final mass

this apply for moles as weel ( if there is no reaction, which is the case )

mol of A initially = mol of A finally

or, for this case

moles of A in stock = moles of A in diluted solution

Recall that

mol of A = Molarity of A * Volume of A

then

moles of A in stock = moles of A in diluted solution

Molarity of A in stock * Volume of A in stock = Molarity of A in diluted solution* Volume of A in diluted solution

Now, substitute known data

30*0.6274 = 725 * M2

M2 = 30*0.6274 /725

M = 0.025961 mo per liter (M)

choose A

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