CHEM 103: FINAL EXAM STUDY GUIDE WITH ANS

CHEM 103: FINAL EXAM STUDY GUIDE WITH

ANS


1. Water (H2O) with a molecular weight of 18 has a boiling point of 100oC

and methane (CH4) with a somewhat similar molecular weight of 16

has a boiling point of -161oC. This difference is much higher than can

be explained by the polarity of water. Explain what causes this

difference.

Hydrogen bonds which are strong intermolecular attractive forces

form between water molecules requiring much more energy to

separate the molecules than for other molecules.




2. Show the calculation of the molar mass (molecular weight) of a

solute if a solution of 14.6 grams of the solute in 200 grams of water

has a freezing point of -1.35oC. Kf for water is 1.86 and the

freezing point of pure water is 0oC. Calculate your answer to 0.1

g/mole. Δtf = Kf ×m




∆tf = Kf x m




molality = ∆tf / Kf = 1..86 = 0.726 m

, molality = (gsolute / MW) / (gsolvent / 1000)




0.726 = (moles) / ()




Moles = 0.726 x 0.200 = 0.1452




0.1452 = (14.6 / MW)




MW = 14..1452 = 100.6




Question 1


1. Convert 0.00346 to exponential form and explain your answer.


2. Convert 2.76 x 104 to ordinary form and explain your

answer. Your Answer:

1. 0.00346 = smaller than 1 = negative exponent, move decimal 3

places = 3.46 x 10-3




2. 2.76 x 104 = positive exponent = larger than 1, move decimal