Midterm for me
Cations: Ag+, Hg22+, Pb2+, Bi3+, Cu2+, As3+, Co2+, Ni2+, Fe3+, Al3+
Anions: SO42-, CO32-, PO43-, Cl-, NO3-
List the cations whose chlorides are insoluble in water. (5 points)
A salt was completely soluble in water. When this solution was treated with AgNO3 no precipitate was formed. What anions could be present? (5 points)
An unknown solution was treated with BaCl2 and a white precipitate formed which did not dissolve in hydrochloric acid. What anion(s) could be present in the unknown solution? (5 points)
What technique(s) would you use to collect a solid product from an aqueous solution?
Describe. (5 points)
Why do you separate the cations in different groups before performing individual tests? How do you separate them into groups? (10 points)
Molecular Weight of a Vapor (20 points)
Calculate the molecular weight of a volatile liquid, if 0.44 g of it occupies 297 mL at 100°C and 750 mmHg. Show your work. (15 points)
Why is it that you do not have to accurately weigh the mass of the liquid that you put in the flask before you start the experiment? (5 points)
Freezing Point Depression (30 points)
A sucrose (table sugar, molar mass 342 g/mol) solution was made by dissolving 68.2 g of sucrose in 800 g of water. What is the molality of the solution? (5 points) What is the freezing point of this solution if Kf of water is 1.86 °C/Molal? (5 points) Show your work
When 0.354 g of an unknown nonelectrolyte compound was dissolved in 12.5 g of benzene a solution was formed that froze at 4.46°C. Calculate the molar mass of the unknown compound. The freezing point of benzene is 5.48°C, and the Kf of benzene is 5.12 °C/Molal. (20 points) Show your work
Extra Credit. When a pure solvent freezes the temperature remains constant till all liquid is frozen (thus the freezing point). When a solution freezes the temperature keeps decreasing. Explain why you do not see a steady and constant freezing point for a solution. (5 points)
Chemical Kinetics (20 points)
Given the rate law for the reaction between A and B,
rate=k[A]〖[B]〗^2
what is the reaction order with respect to A? What is the overall reaction order?
How will the rate change if the concentration of A is doubled and the concentration of B is tripled at the same time? Show your work.
The rate constant is affected by temperature through the Arrhenius equation
k=Ae^(-E_a/RT)
Explain how the temperature impacts the reaction rate (as the temperature increases and decreases). Show your reasoning.
Given the following data for the reaction A → B, determine the activation energy, Ea, of the reaction.
k (M/s) T (K)
0.681 500
0.715 1000
Given the following data, determine the rate law for the reaction
NH4+(aq) + NO2–(aq) → N2(g) + 2H2O( )
Experiment [NH4+] (M) [NO2–] (M) Rate (M/s)
1 0.2500 0.2500 1.25 ×10–3
2 0.5000 0.2500 2.50 ×10–3
3 0.2500 0.1250 6.25 ×10–4