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7.  (WCSP24.[x]) Self-inflating balloons commonly contain a solution of citric acid and solid sodium bicarbonate (baking soda).  When the small packet of citric acid solution is broken, the two components mix to generate carbon dioxide gas.  The balanced reaction is below:   C­6H8O7  (aq) +  3  NaHCO3 (s) 

14. A phase diagram for a substance with a molar mass of 60.1 g/mol is shown below. (WCSP[x]) a. (6 points) Sketch the heating curve for the substance going from -30 °C to 150 °C (point A to point B on the diagram above).  A template is given below. b. (6 points) Calculate the heat required to vaporize 30 g of the substance initially at room temperature (25 ºC). (WCSP[x]) ΔHfus 5.4 kJ/mol ΔHvap 45.1 kJ/mol Cs (solid) 2.45 J/g°C Cs (liquid) 2.26 J/g°C Cs (gas) 2.05 J/g°C Melting point -89.5 °C Boiling point 82.6 °C   Enter the value in the box below.   

(WCSP24) Lactic acid is responsible for muscle soreness after exercise.  a.  What is the molecular formula of lactic acid? C[drop1]H[drop2]O[drop3] b. How many sigma and pi bonds are present in the structure? σ: [drop4] π: [drop5]

4.  (WCSP24.[x], 8 points) Cell phones use electromagnetic radiation with an energy of about 1.08 J/mol of photons.   Calculate the wavelength (in nm) and frequency that can be used to describe light with this energy. Enter the wavelength in nm below.

(WCSP24) When 5.0 g of CaCl2 is dissolved in 25 g of solution, the temperature of the solution increases by 25  ̊C.  Select all of the statements that are true of this process.  

16. Carbon monoxide is a toxic gas.  The upper limit of carbon monoxide (CO) in air is 9 ppm (9.0 x 10-6) over an 8-hour period.  a. At this concentration, how many moles of CO are there in a bedroom with a volume of 29,000 L at 25 oC and 0.98 atm? (3 points, WCSP[x]) b. How many molecules of CO are in the room? (3 points, WCSP[x])   Enter the value from part a in the box below.   

10.  (WCSP24.[x]) Hot air is less dense than cold air and this is the reason that hot air balloons float! A hot air balloon on a cool summer morning is filled with air to a volume of 2.20 x 106 L and warmed to 195 °F (90 °C).  A hot air balloon must be inflated to a volume of approximately 2.60 x 106  L in order to float in air. a. (4 points) At constant pressure, provide a molecular-level explanation of the relationship between temperature and volume of a gas.   b.  (6 points) Calculate the temperature the gas must be (in °C) in order to float.   Enter the temperature below

 (WCSP24) Select the intermolecular force(s) that are present in: CH3CH2OH

8. (WCSP24.[x]) Heavy metals, such as calcium, can be extracted from water by a precipitation reaction.   Hard water has a Ca2+ ion concentration around 4.24 x 10-3 M.   When hard water is mixed with a solution of soda ash (sodium carbonate, Na2CO3), the calcium ions react to form a precipitate and the water is now “softened.”  The precipitate can be removed by filtration. a.  (8 points) Write the complete balanced equation and the net ionic equation that occurs when Ca2+ and sodium carbonate react. Circle the precipitate. b.  (6 points) A 1000 mL soda ash solution was prepared with 5.0 g of sodium carbonate (MW = 106 g/mol).  Calculate the concentration (in M) of the sodium carbonate in the solution.  Calculate the concentration of sodium ions Enter the concentration of sodium ions below.

Suppose we add the following variations to the edges. In which cases is the MST of the original graph still a MST of the updated graph?