Question

HW problems:

1)

Give the net ionic equation for the reaction that occurs when aqueous solutions of lithium

carbonate and barium nitrate are mixed.

2)

Which of the following solutions will have the highest concentration of chloride ions? 0.10 M NaCl, 0.10 M MgCl2, 0.10 M AlCl3, 0.05 M CaCl2, 0.05 M AlCl3, 0.15 M NaCl

3)

What mass (in grams) of NH3 must be dissolved in 650.0 g of methanol to make a 0.250 m

solution?

4)

How many kJ of energy are required to transform 30.00 moles of solid benzene at -20.00 °C to

gaseous benzene at 140.0 °C?

Answer 1

1)Give the net ionic equation for the reaction that occurs when aqueous solutions of lithium

carbonate and barium nitrate are mixed.

Answer : Li₂CO₃(aq) + Ba(NO₃)₂(aq) --> 2Li⁺(aq) + 2NO₃^- (aq) + BaCO₃ (s)

2)

Which of the following solutions will have the highest concentration of chloride ions? 0.10 M NaCl, 0.10 M MgCl2, 0.10 M AlCl3, 0.05 M CaCl2, 0.05 M AlCl3, 0.15 M NaCl

Answer :

The concentrations of Chloride ions will be:

0.10 M NaCl, : 0.1 M ( each molecule will give one Cl^- )

0.10 M MgCl2, : 2X 0.1 = 0.2 M ( each molecule will give two Cl^- )

0.10 M AlCl3, : 3X 0.1 = 0.3 M ( each molecule will give three Cl^- )

0.05 M CaCl2, 2X0.05 = 0.1 M ( each molecule will give two Cl^- )

0.05 M AlCl3,   : 3X0.05 = 0.15 M ( each molecule will give three Cl^- )

0.15 M NaCl   : 0.15 M ( each molecule will give one Cl^- )

So highest concentration is in 0.10 M AlCl3,

3)

What mass (in grams) of NH3 must be dissolved in 650.0 g of methanol to make a 0.250 m

solution?

Molality = mass of solute / molecular weight of solute X weight of solvent (Kg)

mass of solute = ?

molecular weight of solute = 17

weight of solvent (Kg) = 0.65 Kg

Molality = 0.25 = Mass / 17 X 0.65

MAss of ammonia = 0.25 X 17 X 0.65 = 2.7625 grams

4)

How many kJ of energy are required to transform 30.00 moles of solid benzene at -20.00 °C to

gaseous benzene at 140.0 °C?

We need the values like :

boiling point melting point molar heat of fusion molar heat of vapourization etc