Question

1. A calorimetry investigation is performed to determine the heat of neutralization when hydrochloric acid and sodium hydroxide solutions are mixed.
   1. Write the complete chemical equation for the reaction between hydrochloric acid and sodium hydroxide.
   2. Write the net ionic equation for the reaction between hydrochloric acid and sodium hydroxide.
   3. The procedure then calls for measuring 50.00 mL of each 0.10 molar solution. Why is it important to measure the volumes as accurately as possible?
   4. What is the most accurate measuring instrument in your lab for measuring liquid volumes? Explain.
   5. The measured volumes of each solution are put into separate containers and allowed to sit for several minutes. The initial temperature of each solution is recorded as. The solutions are mixed in the coffee cup calorimeter and the highest temperature is recorded. Assume that the acid and base solutions have the same density and specific heat as water. Explain how the measurements are used to calculate the heat produced during the procedur (Use q= mcDT and give the correct units for each term)
   6. Use the net ionic equation from b. to calculate the number of moles of product formed during the procedure.
   7. Use your answers to #e and #f to calculate the value of the heat of reaction, DH, for the procedure in kilojoules per mole. (You can make up your own temperatures if it makes it easier!, but then generalize)
   8. A follow-up activity uses nitric acid and potassium hydroxide solutions as the reactants. The same amounts and the same concentrations of the reactants are used and the same measurements are made. Write the complete equation for this reaction.
   1. Write the net ionic equation for these reactants given in #h.
   10. Predict how the calculated value for the heat of reaction for nitric acid and potassium hydroxide would compare to the calculated value calculated in #g.

Answer 1

#(a): Since hydrochloric acid(HCl) is an acid and sodium hydroxide(NaOH) is a base, acid-base neutralization reaction takes place to form H₂O(l) and NaCl(aq). Hence the complete balanced chemical equation is:

HCl(aq) + NaOH(aq) ----> H₂O(l) + NaCl(aq)

#(b): Since HCl and NaOH are strong acid and bases respectively, they are completely dissociated in water. NaCl is also completely dissociated in water. Hence the completely ionic equation is:

H⁺(aq) + Cl^-(aq) + Na⁺(aq) + OH^-(aq) -----> H₂O(l) + Na⁺(aq) + Cl^-(aq)

Net ionic equation can be obtained by cancelling all the spectator ions. The spectator ions are the ions that are common to both sides. Hence spectator ions are: Cl^-(aq) and Na⁺(aq). Hence net ionic equation is:

H⁺(aq) + OH^-(aq) -----> H₂O(l) (Answer)

#(c): Volume needs to be accurately measure because higher volume will lead to higher moles of either of the reactant or both. This will also change the volume of the solution. Since enthalpy of neutralizaiton is measure per mole of the reactants, the experimental enthalpy of neutralization will not be accurate.

#(d): The most accurate measuring instrument for measuring liquid volume available in lab are graduated cylinder.

Because graduated cylinders are thinner than beaker and more graduated mark and are designed to measure with error within 0.5%.