View the step-by-step solution to:

1. Sodium phosphate, Na3PO4, is sold over the counter for use in households as a cleaning agent and a degreaser. (13 points) a. Is sodium phosphate

1. Sodium phosphate, Na3PO4, is sold over the counter for use in households as a cleaning agent and a degreaser. (13 points)
a. Is sodium phosphate is an ionic compound? What does this mean in terms of structure? Given its structure, would you calculate the atomic mass, molecular mass, or formula mass of sodium phosphate? (2 points)
b. What is this value for Na3PO4? (2 points)
c. How many moles of Na3PO4 are in 5.00 g of sodium phosphate? How many moles of Na+are in 5.00 g of sodium phosphate? How many sodium ions are in 5.00 grams of sodium phosphate? Use Avogadro’s number, 6.0221 ? 1023 ions/mol. (3 points)
d. You make a solution of sodium phosphate by mixing 243 g of Na3PO4 with 2.00 L of water in a beaker. What is the molarity, or moles/L, of the resulting solution, assuming all of the solute dissolves? (3 points)
e. While mixing the sodium phosphate and water in the beaker, you notice the solution becomes warm to the touch. What makes up the system? What makes up the surroundings? What is the direction of heat transfer when sodium phosphate is dissolved in water? (3 points)




2. Premarin is a drug used to treat ovary-function deficiencies in women. The drug contains only carbon, oxygen, and hydrogen. A 100.0 g sample of premarin produced 293.0 g of carbon dioxide and 73.32 g of water when analyzed by combustion analysis. The molecular mass of premarin is 270.356 g/mol. (22 points)
a. How many moles of carbon were present in the 100.0 g sample? Think about how many moles of CO2 were produced and how that relates to moles of carbon in the sample. (3 points)
b. How many moles of hydrogen were present in the 100.0 g sample? Think about how many moles of H2O were produced and how that relates to moles of hydrogen in the sample. (3 points)
c. What is the mass percent of carbon in premarin? Convert your answer to part a to grams, then figure out what mass percent of the sample was carbon. (3 points)
d. What is the mass percent of hydrogen in premarin? Convert your answer from part b to grams, then figure out what mass percent of the sample was hydrogen. (3 points)
e. What is the mass percent of oxygen in premarin? From your answers to parts c and d, you already know the mass percents of carbon and hydrogen. (2 points)
f. How many moles of oxygen were present in the 100.0 g sample? Figure out how many grams of the sample were oxygen using your answer to part e, then convert to moles. (3 points)
g. What is the empirical formula for premarin? Use your answers to parts a, b, and f. (3 points)
h. What is the molecular formula for premarin? Calculate molar mass for the empirical formula, then compare it to the molecular mass of premarin to determine the molecular formula. (2 points)




































3. A 0.250 L solution of 0.846 M hydrochloric acid is used to neutralize a 25.0 g sample of strontium hydroxide in a coffee-cup calorimeter. Strontium chloride, used as a red-flame coloring agent in fireworks, is produced by the reaction. The temperature in the calorimeter was observed to rise from 20.0°C to 30.1°C during the neutralization. Assume the density of the hydrochloric acid solution is 1.00 g/mL, and that the specific-heat capacity of the system is the same as that for water, 4.18 J/g-K. Assume only water is available to absorb or release heat, and that the reaction is at constant pressure. (21 points)
2 HCl(aq) + Sr(OH)2(aq) → SrCl2(aq) + 2 H2O(l)
a. How many moles of HCl are there? Use that number to calculate the maximum yield of SrCl2. How many moles of Sr(OH)2 are there? Use that number to calculate the maximum yield of SrCl2. Is HCl or Sr(OH)2 the limiting reagent in the neutralization reaction? (7 points)
b. How many moles of Sr(OH)2 are neutralized by the HCl? How many moles of excess reagent were left over? To find how many moles were left over, subtract the number of moles neutralized from the original number of moles of Sr(OH)2. (3 points)
c. If 12.3 g of strontium chloride were obtained after the neutralization was complete, what was the percent yield? Determine how many moles of SrCl2 should theoretically be produced by the reaction. Convert that number to grams, and determine the percent yield. (4 points)
d. What was the enthalpy change (in kJ) for the system in the coffee-cup calorimeter? ΔH = -mcpΔT . Figure out how many grams of hydrochloric acid there are assuming its density is 1 g/ml. Don’t forget about the mass of the Sr(OH)2. Make sure to convert the T from °C to °K.. Assume that the specific heat capacity of the system is the same as that for water, 4.18 J/g-K. (5 points)
e. What was the heat of reaction per mole of water produced? You already have figured out how many moles of HCl were consumed. Use that number to figure out how many moles of water were produced. Then use your answer to part d to figure out the heat of reaction if a mole of water was produced. (2 points)
























4. Heptane, C7H16, is an undesirable component of gasoline. Heptane burns explosively and causes engine knocking in automobiles. The thermochemical equation for the combustion of heptane is shown below. (14 points)
C7H16(l) + 11 O2(g) → 7 CO2(g) + 8 H2O(g) ΔH°rxn = -4,820 kJ
a. Find the heat of formation for heptane using the heat of combustion for heptane and the following three formation reactions. (5 points)
C(s, graphite) + O2(g) → CO2(g) ΔH°f = -394 kJ
H2(g) + ½ O2(g) → H2O(g) ΔH°f = -242 kJ
7 C(s, graphite) + 8 H2(g) → C7H16(g) ΔH°f = ?
Remember that the heat of formation for a reaction is equal to the heat of formation of the products minus the heat of formation of the reactants. Make sure to take into account the number of moles of each product and reactant.
b. What is the heat of reaction for the combustion of heptane, in kcal/mol? Convert the heat of reaction given above to cal, using the following relationship: 4.184 J = 1 cal. (2 points)
c. Before heptane combusts, what type of energy is present in the system? Is it kinetic or potential energy? Where is this energy stored? (2 points)
d. After heptane combusts, what type of energy is associated with the explosion? Is it kinetic or potential energy? (2 points)
e. Heptane can appear harmless, but when ignited, it explodes violently. What is the first law of thermodynamics? Use your answers to parts c and d to write an equation using Ek and Ep that shows how this reaction obeys the first law of thermodynamics.

Recently Asked Questions

Why Join Course Hero?

Course Hero has all the homework and study help you need to succeed! We’ve got course-specific notes, study guides, and practice tests along with expert tutors.

-

Educational Resources
  • -

    Study Documents

    Find the best study resources around, tagged to your specific courses. Share your own to gain free Course Hero access.

    Browse Documents
  • -

    Question & Answers

    Get one-on-one homework help from our expert tutors—available online 24/7. Ask your own questions or browse existing Q&A threads. Satisfaction guaranteed!

    Ask a Question