5. When a student mixes 50 mL of 1 M HCI and 50 mL of 1 M NaOH in a coffee-cup c

Question

5. When a student mixes 50 mL of 1 M HCI and 50 mL of 1 M NaOH in a coffee-cup calorimeter, the temperature of the resultant solution increases from 21.0 C to 27.5 °C a) Find the moles of each reagent. Which of the reagents is the limiting one? b) Calculate the heat gained by solution. (Use the equation Q s m AT assume that s, the specific heat of the solution, is 4.18 J/g-K. m s the total mass of solution (density i gmL) and ?? is the change in temperature c) Using the above data calculate the enthalpy of the reaction (for 1 mol of HCl with 1 mol NaO1H) assuming that the calorimeter does not lose any heat.

Explanation / Answer

Calorimetric expeiment

a) moles HCl = 1 M x 0.050 L = 0.05 moles

moles NaOH = 1 m x 0.05 L = 0.05 moles

Both reagents are in equal amounts.

Both are limiting to each other

b) heat gained by solution = mCpdT

                                          = 100 x 4.18 x (27.5 - 21) = 2717 J

density of water = 1 g/ml

100 ml solution = 100 ml x 1 g/ml = 100 g

c) enthalpy dH

dH = 2717 J/0.05 mol x 1000 = 54.34 kJ/mol

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