a) Formaldehyde (CH2=O) is the simplest aldehyde and is miscible in ethanol.
i) Would the following intermolecular interactions be present or absent for an ethanol-formaldehyde mixture: hydrogen bonding, London dispersion, ion-ion, and dipole-induced dipole. [8 marks]
ii) 66 g of formaldehyde is dissolved in 800 g of ethanol. Given that the density of ethanol 789 g L-1, calculate the molarity, molality, and mole fraction for this solution. [20 marks]
iii) Ethanol has a freezing point depression coefficient Kfp = -1.99 K kg mol-1. Given that the freezing point of pure ethanol is -114.6°C, what temperature does this ethanol-formaldehyde mixture freeze at? [22 marks]
Formaldehyde is miscible in ethanol
H2C=O- - - - HO-CH2-CH3
The interactions are present in molecule such as hydrogen bonding, London Forces, ion ion interactions and induced dipole interactions. c=O bond of formaldehyde exists as a dipole. Since, oxygen is more electronegative than carbon it withdraw electron pair towards itself. It becomes partially negatively charged and carbon become partially positively charged.
2). MOLARITY:
GIVEN mass of formaldehyde= 66g
Molar mass of formaldehyde=30g / mol
Number of moles of formaldehyde= 66/30=2.2 moles
Mass of solution=66+800=866g
Density of ethanol=789g/L
Volume of 800g of ethanol= 800/789~1Li.e 1000mL
Molarity= no. Of moles/ volume of solution in L=2.2M
MOLALITY:
NO. OF moles= 2.2
Mass of solvent=800g
Molality=2.2×1000/800mol/g=2.75m
MOLE FRACTION:
Mole fraction of formaldehyde:
No. Of moles of formaldehyde=2.2moles
Molar mass of ethanol=46g/mol
No. Of moles of ethanol=800/46=17.39 moles
Mole fraction of A=no. Of moles of A/ total no. Of moles(A+B)
Mole fraction of formaldehyde=2.2/2.2+17.39)=2.2/19.59=0.11
Total mole fraction=1
Mole fraction of ethanol=1-0.11=0.89
3).∆Tf=Kf.m
∆Tf= depression in freezing point=To-Ts
Kf=constant
m= molality of solution
∆Tf=-1.99×2.75=-5.47
To=-114.6
Ts=To-∆Tf=-114.6+5.47=-109.13°C
a) Formaldehyde (CH2=O) is the simplest aldehyde and is miscible in ethanol. i) Would the following...
Which of the following best describes London dispersion forces. Question 1 options: the intermolecular forces that exist when ions from an ionic compound are attracted to the dipole of polar molecules in a mixture. involves molecular orientations in which the positive end of one dipole is near the negative end of another forces that exist only between molecules that contain hydrogen atoms bonded to highly electronegative atoms such as O, N, F. Interactions between temporary dipoles cause atoms to be...