When ammonium compounds are heated with sodium hydroxide or calcium hydroxide, ammonia is liberated. The ionic equation for the reaction is shown. $$\[ \mathrm{NH}_{4}^{+}+\mathrm{OH}^{-} \rightarrow \mathrm{NH}_{3}+\mathrm{H}_{2} \mathrm{O} \]$$ FA 1 is prepared by heating $$\(10.0 \mathrm{~cm}^{3}\)$$ of aqueous ammonium chloride, $$\(\mathrm{NH}_{4} \mathrm{Cl}(\mathrm{aq})\)$$, with $$\(25.0 \mathrm{~cm}^{3}\)$$ of $$\(2.00 \mathrm{moldm}^{-3}\)$$ sodium hydroxide, NaOH . The sodium hydroxide is in excess. The reaction mixture is cooled and diluted to $$\(250 \mathrm{~cm}^{3}\)$$ with distilled water. You will determine the concentration of the aqueous solution of ammonium chloride by titrating the remaining sodium hydroxide from the preparation of FA 1 with a known concentration of sulfuric acid. $$\[ 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \rightarrow \mathrm{Na}_{2} \mathrm{SO}_{4}(\mathrm{aq})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \]$$ FA 2 is 0.0520 mol dm $$\(^{-3}\)$$ sulfuric acid, $$\(\mathrm{H}_{2} \mathrm{SO}_{4}\)$$. FA 3 is bromophenol blue indicator. Method - Support the cup in the $$\(250 \mathrm{~cm}^{3}\)$$ beaker. - Use the $$\(25 \mathrm{~cm}^{3}\)$$ measuring cylinder to transfer $$\(25.0 \mathrm{~cm}^{3}\)$$ of distilled water into the cup. - Place the thermometer in the water and tilt the cup, if necessary, so that the bulb of the thermometer is fully covered. Record the temperature of the water in the space for results. - Weigh the container with FA 4. Record the mass. - Add all of FA 4 to the water in the cup. - Stir the mixture gently so that FA 4 dissolves. - Measure and record the minimum temperature reached. - Calculate and record the change in temperature. - Weigh the container with any residual FA 4. Record the mass. - Calculate and record the mass of FA 4 added to the cup. Results

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