EFFECT OF CONCENTRATION ON RATE OF REACTION
The rate of a chemical reaction depends on the frequency of the collisions between the atoms or ions of the reactants. In this investigation the rate at which aluminum replaces hydrogen from a solution of hydrochloric acid will be observed.
» Test tube, 16 x 150 mm
» Test tube clamp
» Beakers 100 mL/3.4 oz, 400 mL/13.5 oz
» Glass right angle bend
» Rubber stoppers #0, 1 hole
» Rubber tube 5/16" x 18"
» Safety goggles
» Aluminum metal
» Hydrochloric acid, 1.0N HCI
» Stopwatch or clock with second hand
» Laboratory burner or a candle
Add strands of aluminum metal to 16 x 150 mm test tube. If any strands are longer than 1-1/2", bend them in half.
Moisten the hole in the #0 rubber stopper and also one end of the glass right angle bend. Carefully insert the right angle bend into the stopper. Attach the rubber tube to the other end of the glass bend. Set the stopper assembly aside for now.
Put on your safety goggles and gloves. Add just enough 1.0N hydrochloric acid, HCI, to the test tube to cover the aluminum metal, not over 1-1/2" (38.1 mm).
Note: The aluminum metal has an oxide coating on its surface. This coating acts as a barrier between the metal and the acid, and it prevents the reaction from proceeding at its maximum rate.
While holding the test tube at a 45-degree angle, gently warm the acid solution, do not boil (a candle could be used as the heat source). The warm acid will gradually remove the oxide coating, and the rate of reaction between the aluminum and the acid will increase.
Insert the stopper assembly into the test tube. Use the 13.5 oz./400 mL beaker to support the test tube.
Fill the 3.4 oz/100 mL beaker with water. Place the free end of the rubber tube in the beaker.
Observe the rate at which bubbles of hydrogen gas are escaping from the end of the rubber tube.
As soon as the rate slows down to the point where it is possible to count each bubble as it rises to the surface, begin taking data. While one person keeps track of time, another counts bubbles released.
Count the number of bubbles released in 30 seconds. Repeat, this process, counting the number of bubbles released in 30-second intervals, for a total of at least eight, 30-second time segments, or until the number of bubbles released during a 30-second interval has dropped to about 4. Record all data.
As the concentration of the reactants decreases, the frequency of collisions decreases, and the rate of the reactions slows down.