Constants | Periodic Table Using the van\'t Hoff factors in the table below, cal

Question

Constants | Periodic Table Using the van't Hoff factors in the table below, calculate the mass of solute required to make each aqueous solution. Van't Hoff factors at 0.05 m concentration in aqueous solution Solute Nonelectrolyte NaCl MgSO4 MgCl2 K2SO4 FeCl3 Expected Measured 2.7 2.6 3.4 4 You may want to reference (Pages 609- 610) Section 13.7 while completing this problem. Part A Calculate the mass of solute required to make a sodium chloride solution containing 159 g of water that hasa melting point of -1.5 °C Express your answer using two significant figures. Submit Request Answer

Explanation / Answer

Freezing point depression = I( Van't Hoff factor)*m( molalirty)*Kf( Freezing point depression constant)

for NaCl, i= 1.9 ( measured)

m= molality= moles of NaCl/kg of solvent water= moloes of NaCl/ (159/1000)= moles of NaCl/0.159=6.3* moles of NaCl

Kf= 1.86 deg.c/m, Freezing point depression =Freezing point of water- Freezing point of solutio n=0-(-1.5)= 1.5 deg.c

hence 1.5= 1.9*6.83* moles of NaCl*1.86

moles of NaCl= 1.5/(1.9*6.83*1.86)= 0.062 moles

mass of NaCl= moles* molar mass = 0.062*58.5 =3.63 gm

2. for magnesium sulfate, Osmotic pressure = i*C*RT

C= concentration of solute= mass of solute/ liter of solution , R= gas constant= 0.0821 L.atm/mole.K and T= 309K,. i= 1.3 measured for MgSO4, volume of solution =261 ml = 261/1000L

3.95= 1.3* moles of MgSO4* 0.0821*309/(261/1000)

moles of MgSO4= 0.041

mass of MgSO4= moles* molar mass = 0.041*120.3 =4.93 gm

3. Boiling point elevation,c deltaT= boiling point of solutino- boiling point of water= 111-1000=11 deg.c

Boiling point elevation = i*m*Kb( boiling point elevation constant)

11= 3.4*m*0.512

m= 6.31

Moles of FeCl3/ kg of solvent = 6.31

kg of solvent = 253/1000 =0.253 kg

moles of FeCl3= 0.253*6.31 =1.59

mass of FeCl3= moles* molar mass =1.59*162.5 gm =258.4 gm

=

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