# Molarity, Molar mass, Molar Heat

4. The term proof is defined as twice the percent of volume of pure ethanol in solution. Thus a solution that is 95% ethanol by volume is 190 proof. What is the molarity of ethanol in a 92 proof ethanol water solution? (density of ethanol is .8g/cm3; mol. wt. of ethanol is 46).

6. Find the mass percent of CuSO4 in a solution whose density is 1.3g/mL and whose molarity is 1.22M.

8. When .800g of NH4NO3 was added to 150g of water in a cup, the temperature dropped by .413 degrees centigrade. The heat capacity of water is 4.18J/degree centigrade. Assume the specific heat of the solution equals that of pure water and the calorimiter is ideal. What is the molar heat of solution of solid NH4NO3?

9. At a given temp., you have a mixture of benzene (vapor pressure is 745 torr), and toluene (vapor pressure is 290 torr). The mole fraction of the benzene in the solution is .590. Assuming ideal behavior calculate the mole fraction of the toluene in the vapor above the solution.

11. You have a 10.4g mixture of sugar (C12H22O11) and table salt (NaCl). When this mixture is dissolved in 150g of water the freezing point is found to be -2.24 degrees centigrade. Calculate the percent by mass of sugar in the original mixture.

13. A 5.5 g sample of a compound is dissolved in 250g of benzene. The freezing point of this solution is 1.02 degrees centigrade below that of pure benzene. What is the molar mass of this compound? (Kt for benzene is 5.12degrees C/m).

14. If .455g of Thyroxine is dissolved in 10g of benzene, the freezing point of the solution is 5.144 degrees centigrade. Pure benzene freezes at 5.444 degrees centigrade and has a value for the molal freezing point depression constant Kt of 5.12 degrees centigrade/m. What is the molar mass of Thyroxine?

15. Knowing that delta H of vaporization for water is 40.7kj/mol, calculate P of vaporization of water at 37 degrees centigrade.

18. Calculate the molarity of a solution containing KCl and water whose osmotic pressure at 21 degrees centigrade is 100 torr. Assume complete dissociation of the salt.

19. A .2M solution of MgSO4 has an observed osmotic pressure of 7.8atm at 25 degrees centigrade. Determine the observed van't Hoff factor for the experiment.

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#### Solution Summary

The solution answers 10 short first year problems on molarity, molar mass , molar heat of solution, mole fraction, percent by mass of sugar, vaporization, van't Hoff factor etc.

Chemistry Problems

1. The following reaction occurs:

CaCO3 + 2H- -> Ca2+ + CO2 +H2O

If a 25gm sample of calcium carbonate is added to a 75.5 ml HCl (density = 1.125gm/cm3, 26% HCl by mass), calculate the molarity of the HCL remaining in solution (if any) after the reaction is complete. Assume no volume change.

2. A sample of cocaine, C17H21O4N, is diluted with sugar C12H22O11. When a 1.00mg sample of this mixture is burned, 1.00ml of carbon dioxide (density 1.8gm/l) is formed. What is the percentage of cocaine in the mixture?

3. NH4ClO4 is used in a space shuttle along with aluminum metal. The products of the reaction are aluminum oxide, aluminum chloride, NO, and steam. The reaction mixture contains 5.75gm of Al and 7.32gm of NH4ClO4.

a. What is the theoretical yield of the Aluminum chloride? Note that not all of the chloride comes from NH4ClO4.

b. If 1.87gm of Aluminum chloride is formed, what is the percent yield?

4. A 1.58gm sample of C2H3X3 (g) has a volume of 297ml at 769mm of Hg and 35 degrees centigrade. What is element X?

5. What volume of ethane (C2H6), measured at 23.0 degrees centigrade and 752mm Hg, would be required to heat 855gm of water from 25 degrees centigrade to 98 degrees centigrade (H= -226.2kJ/mole)

6. Brass has a density of 8.25gm/cm3 and a specific heat of .363 J/gm degrees centigrade. A cube of brass 7.5mm on an edge is heated on a flame at temperature 95 degrees centigrade. It is then immersed into 20ml of water at 22 degrees centigrade in an insulated container. Assuming no heat loss, what is the final temperature of the water?

9. A water solution containing 28% by mass Iron(III) chloride has a density of 1.271 gm/cm3. Assuming ideal behavior calculate the:

a. Molarity

b. Molality

c. Osmotic pressure at 25 degrees centigrade

d. Boiling point

10. The solution of iron(II) hydroxide, Fe(OH) 2 is 1.43x10-3 gm/liter at 25 degrees centigrade.

a. Write a balanced equation for the solubility at equilibrium.

b. Write the expression for the solubility product constant Ksp, and calculate its value.

c. Calculate the pH of a saturated solution of Fe(OH) 2 at 25 degrees centigrade.

d. A 50ml sample of 3.00x10-3 molar FeSO4 solution is added to 50ml of 4.00x10-6 molar NaOH solution. Does a precipitate of Fe(OH) 2 form? Explain and show calculations to support your answer.