7. Al metal has a specific heat of 0.880 J/gram-degree C. How many joules of hea

Question

7. Al metal has a specific heat of 0.880 J/gram-degree C. How many joules of heat are needed to heat 562grams of Al from 25.0oC to 95.0oC ?

8. The enthalpy of combustion of C2H6 is 1541kJ/mole. How many kJ of heat result when 775 grams of C2H6 are combusted ?

9. Explain why although both NaCl and sucrose, C12H22O11 , are soluble in water one of their solutions conducts electricity, but the other does not.

10. A sample of a hydrate of NiCl2 weighing 0.235 grams is heated to drive off the water leaving a weight of 0.128 grams. What is the formula of the hydrate ? i.e. What is the value of X in NiCl2(XH2O)

Explanation / Answer

Heat required = mass * specific heat * temp difference

                    = 562 g * 0.88J/goC * (95-25)= 34619.2 J

34619.2 J energy is required to heat the metal to 95oC

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Mol. Wt of C2H6 = 34g/ mole

Heat evolved when 1 mole of C2H6 is combusted = 1541 kJ/mole

moles of c2H6 combusted = 775g/34gmole-1 = 22.79 moles

Amount of heat evolved = 22.79 moles * 1541 kJ/mole = 35119.39 kJ

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NaCl when dissolved in water, ionize in Na+ and Cl-. Due to the presence of ions the solution conducts electricity. Sucrose dissolves in water and does not ionize. As there is no ions present , the solution does not conduct electricity.

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Weight of the moisture = weight of hydrated NiCl2 - weight of heated compound

                                 = 0.235- 0.128 = 0.107 g

moles of water = 0.107 /18 = 0.006 moles

moles of NiCl2 = 0.128/129.59 = 0.00098 moles

Mole ratio = 0.00098 moles/ 0.006 moles =1/6

x = 6

Formula of the salt = NiCl2.6 H2O

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