Chemistry Questions: Solutions and Reactions

Question 1: Radioactive Decay of Cu-64

Read each question carefully and provide the correct answer. In order to receive full (or partial) credit, YOU MUST SHOW ALL YOUR WORK (all calculations and units where appropriate), AND YOU MUST USE DIMENSIONAL ANALYSIS. The final answer must be enclosed in a box and must have the correct number of significant figures and units. Make sure all reactions are balanced, if they are not; write the balanced reaction in the document

1. A nuclear technician was accidentally exposed to Cu-64 while doing a PET scan for possible tumors. The error was not discovered until 38.1 hours later, when the activity of the sample was 2 µCi.

a. Write the balanced nuclear equation for the decay of Cu-64 (HINT: the imaging tool is useful)

b. If K-42 has a t1/2 12.7 hrs, what is the original activity of Cu-64?

c. Convert the activity you just calculated in (1b) to desintegrations per second (dps)

2. Na-24 is used to treat chronic leukemia among others. It is administered in the form of 24NaCl solution with a dosage of 180 µCi/kg body weight.

a. What dosage (in mCi) would be administered to a 68 kg patient?

b. If the solution is available as 6.5 mCi/mL of solution. How many mL of the solution are needed to treat the patient?

5. Which of the following statements is/are FALSE for the reaction below (mark with an “X”). In order to receive full credit, you must correct the statements. P4(s) + 6 Cl2(g) → 4 PCl3(l) + 304.0 kcal

_____ Heat is absorbed.

_____ This reaction is exothermic.

_____ Heat is a reactant.

_____ This reaction has a negative ΔH or q

6. Consider the reaction: N2 + O2 → 2 NO ΔH = 43.2 kcal. Calculate the heat (in Joules) when 44.9 g of NO are produced.

a. in this reaction, is heat absorbed or released? Circle the correct answer

8. Which of the following will you do to make a reaction go slower? (Mark with an “X”)

______ Increase the concentration of the reactants

______ Cool down the reaction

______ Add a catalyst

9. The equilibrium constant expression (K) for the reaction 2 K(s) + 2 H2O(l) ? 2 KOH(aq) + H2(g), is

11. Consider the reaction system: 2 H2S(g) + 3 O2(g) ? 2 SO2(g) + 2 H2O(g) ΔH = -1036 kJ Which of the following changes will shift the reaction toward reactants? (Mark with an “X” the correct statements).

____ Adding H2S (g) ____ Removing H2O (g) ____ Cooling the reaction

____ Removing O2 (g) ____ Adding SO2 (g) ____ Heating the reaction

____ Increasing the pressure. ____ Increasing the volume

12. Identify the phase change and the sign (+ or -) for the enthalpy for the following processes:

a. H2O(l) → H2O(g) phase change:__________________ ΔH: ______

b. CO2(g) → CO2(s) phase change:__________________ ΔH: ______

14. An ideal gas has a volume of 10.8 L at a temperature of 25.0 °C and a pressure of 1.60 atm. The pressure of the gas is reduced to 370.0 mmHg, but the temperature and number of moles of the gas are kept constant.

a. What is the new volume of the gas (in L)?

b. Which simple gas law explains this behavior? _______________

15. Calculate the volume of 359 g of ethane gas (C2H6) at STP

16. A mixture of gases containing N2, O2, and He is placed in a 25.0 mL container at 298 K. The total pressure of is 760. mm Hg. If the partial pressures of N2 is 90.0 mm Hg and of O2 is 270. mm Hg, What is the partial pressure of He (in atm)?

24. At 88 °C the solubility of potassium nitrate is 88 g per 100. g of water. If 1.53 moles of potassium nitrate are added to 150 mL of water at 20°C, Is the solution, unsaturated, saturated or supersaturated? Provide the appropriate calculations or explanations to support your answer.