Question

4.6 gm of methyl alcohol is dissolved in 25.2 gm of water calculate percentage by mass of methyl alchohol & mole fraction of methyl alcohol and water



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Answer 1

Explanation:

Volume of methyl alcohol =4.6cm3

Density of methyl alcohol =0.7952gcm−3

⇒Density=VolumeMass

⇒0.7952=4.6Mass

⇒Mass=3.657g

∴ Mass of methyl alcohol =3.657g

(i) % by mass of methyl alcohol =mass of methyl alcohol+mass of watermass of methyl alcohol×100=3.657+25.23.657×100=12.6%

(ii) Mole fraction of methyl alcohol and water-

Moles of methyl alcohol =Molecular mass of methyl alcoholMass of methyl alcohol

Molecular mass of methyl alcohol (CH3OH)=12+4×1+16=32g

∴ Moles of methyl alcohol =323.657=0.114

Moles of water =Molecular mass of waterMass of water=1825.6=1.42

Total no. of moles = moles of methyl alcohol + moles of water =0.114+1.42=1.534

∴ Mole fraction of methyl alcohol =total no. of molesmoles of methyl alcohol=

Answer 2

Answer:

1.925

Explanation:

Volume of methyl alcohol =4.6cm

3

Density of methyl alcohol =0.7952gcm

−3

⇒Density=

Volume

Mass

⇒0.7952=

4.6

Mass

⇒Mass=3.657g

∴ Mass of methyl alcohol =3.657g

(i) % by mass of methyl alcohol =

mass of methyl alcohol+mass of water

mass of methyl alcohol

×100=

3.657+25.2

3.657

×100=12.6%

(ii) Mole fraction of methyl alcohol and water-

Moles of methyl alcohol =

Molecular mass of methyl alcohol

Mass of methyl alcohol

Molecular mass of methyl alcohol (CH

3

OH)=12+4×1+16=32g

∴ Moles of methyl alcohol =

32

3.657

=0.114

Moles of water =

Molecular mass of water

Mass of water

=

18

25.6

=1.42

Total no. of moles = moles of methyl alcohol + moles of water =0.114+1.42=1.534

∴ Mole fraction of methyl alcohol =

total no. of moles

moles of methyl alcohol

=

1.534

0.114

=0.075

Mole fraction of water =

total no. of moles

moles of water

=

1.534

1.42

=0.925