This is a sample lab practical for for the chem final I take on Tuesday night! I

Question

This is a sample lab practical for for the chem final I take on Tuesday night! If you could answer the questions so I know exaclty how to do them and can do well that'd be great! Thank you!

Chemistry 211   Lab Final Study Guide   Spring 2015

Useful Information:
1 ampere =coulomb/sec
Faraday’s constant = 96,500 coulombs/mole of electrons
Molar mass of Au = 197.0 g/mole, Molar mass of Cu = 63.55 g/mole
m = moles ,   '   ’

c   kg

Tf

= Tf

Tf

where Tf is for the pure solvent and Tf

is for the mixture.

T = (K

)(m ) ,

m = (

(mass of

solute, g )
)(   ).

f   f   c

c   molar

mass, g

mol 1

mass of

solvent, kg

1.   A student weighs out 1.556 g of t-butyl alcohol into a large test tube. He then measures the freezing point of the t-butyl alcohol (the pure solvent) as 20.6 oC. He then weighs out 1.056 g of water and adds it to the test tube with the t-butyl alcohol. He then measures the freezing point of the mixture to be 14.3 oC.
a)   What is the freezing point depression of the mixture?

b)   What is the freezing point depression constant, Kf of t-butyl alcohol?

2.   If you have a solution of KI that is 1.246 M and you take 200.0mL of the solution and dilute to 1000.0mL, what is the molarity of the final solution?

3.   If you need 16.53mL of 0.0928M NaOH to reach the equivalence point in a reaction with 0.362 grams of an unknown weak acid, what is the molar mass of the unknown acid?

Explanation / Answer

Freezing point depression = Freezing point of t-butyl alcohol+ water - ( freezing point of alcohol =

14.3-20.6= -6.3 deg,c

Freezing point depression = kf*m

Moles = mass/ Molecular weight, mass of solvent = 1.056/1000 kg

Molalty = moles of solute/ kg of solvent = (1.556/74)*1000/1.056=19.91

6.3= kf*19.91

Kf= 6.3/19.91=0.316

2. Moles in 200ml of 1.246M= 1.246*0.2 = 0.2492

from 0.2492= 1L(1000ml)*M1

M1= molarity =0.2492

3. moles of NaOH= 0.0928*16.53/1000=0.001534

moles of acid required at equivalence point =0.001534

Moles = mass/Molar mass

Molar mass= mass/Moles = 0.362/0.001534 =235.98

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.