Answer to Question #103863 in General Chemistry for Beverlie

Question

3. You have learned that adding table salt, NaCl (58.44 g/mol, 2.16 g/cm3), to water (Kb  0.52oC/m) increases the temperature at which it boils. You decide to try cooking pasta faster at a higher temperature in boiling salty water. What increase in the boiling point do you expect if you add 4 tablespoons (1 tbsp  14.8 cm3) of salt to 16 oz of water (474 mL)?

4. The standard molar entropy of lead (II) bromide (PbBr2) is 161 J/mol  K. What is the entropy of 2.45 g of PbBr2?

Answer 1

3)

Mass of 4 tablespoons of table salt =$4*volume*density=4*2.16*14.8 = 127.8 g$

converting this into moles we get

moles of NaCl added = 127.8/58.44 = 2.18

molality of the solution = 2.18/0.474 = 4.62m

$\Delta T_b=m*K_b \newline \Delta T_b=4.62*0.52 = 2.40$

4) Molar mass of PbBr₂ = 367 g

we have to find out the entropy of 2.45g of PbBr₂

which is equal to $\dfrac{2.45}{367}*161 = 1.07J/molK$