Question

a) Write a procedure that you would follow to demonstrate the effect of increasingly higher concentrations of hydrochloric acid on its rate of reaction with antacid tablets. You have seen examples of procedures involving the effects of surface area and temperature on this reaction in the lesson and in the Support Questions. Only use the materials listed in the lesson. (5 marks) b) Design a table (giving headings only) for your observations. (2 marks) c) Describe and explain three safety procedures you would have to follow when performing your procedure in a laboratory setting. (3 marks) d) For the procedure that you designed in part (a), describe three different controls you used

Answer 1

1. Short Procedure

measure 10 ml of 1.0M acid and dilute it with 100 ml of water to make .1M acid
measure 10 ml of .1M acid and dilute it with 100 ml water to make .01M acid

Keep track of which is which!

Grind up several antacid tablets and weigh out one portion, about .5g and record how much it weighs. Drop the powder into a beaker filled with one molarity of acid with your scoop and time how long it takes for the reaction to stop. Record this and repeat for the different concentrations of acid.

Detailed procedure:

Some (but not all) antacid tablets contain primarily calcium carbonate, along with flavoring, binders, and other inactive ingredients. These tablets neutralize excess stomach acid, which is actually dilute hydrochloric acid, according to the following equation:

CaCO₃(s) + 2HCI(aq) → CaCI₂(aq) + CO₂(g) + H₂O(I)

We’ll use exactly this reaction to observe and quantify the effect of concentration of reaction rates.

Required Equipment and Supplies

• goggles, gloves, and protective clothing
• balance and weighing paper
• graduated cylinder, 100 mL
• thermometer
• timer
• foam cup (3)
• marking pen
• calcium carbonate antacid tablets (3)
• hydrochloric acid, 4 M (100 mL)
• hydrochloric acid, 2 M (100 mL)
• hydrochloric acid, 1 M (100 mL)
• water

Substitutions and Modifications

• You may substitute small (~ 1 cm) pieces of chalk (calcium carbonate) for the calcium carbonate antacid tablets.
• In making up the dilute hydrochloric acid solutions, you may substitute muriatic acid from the hardware store, which is typically 31.45% (10.3 M), for reagent grade hydrochloric acid, which is typically 37% (12 M). Adjust quantities accordingly.

Procedure

1. If you have not already done so, put on your splash goggles, gloves, and protective clothing.
2. Label three foam cups 4 M, 2 M, and 1 M.
3. In the first foam cup, make up 100 mL of 4 M hydrochloric acid by adding 33.3 mL of 12 M HCl to 66.7 mL of water. Again, make sure that the combined mass of the foam cup, antacid tablet, and 100 mL of hydrochloric acid is less than the maximum capacity of your balance. If not, reduce the quantity of hydrochloric acid accordingly.)
4. In the second foam cup, make up 100 mL of 2 M hydrochloric acid by adding 16.7 mL of 12 M HCl to 83.3 mL of water.
5. In the third foam cup, make up 100 mL of 1 M hydrochloric acid by adding 8.3 mL of 12 M HCl to 91.7 mL of water.

CAUTION: Add Acid to Water and Wait

6. Weigh one of the antacid tablets to 0.01 g and record its mass on Line A of Table.
7. Place the first foam cup with 4 M hydrochloric acid on the balance and record the mass to 0.01 g on Line B of Table.
8. Measure and record the temperature of the HCl solution on Line C of Table.
9. With the cup and its contents still on the balance, drop the antacid tablet into the cup.
10. Note the combined mass of the cup, acid, and tablet every five seconds and record each mass in Table. (It may be helpful to have one person watching the clock while another calls out the mass reading at each 5-second milestone.)
11. Continue recording the changing mass until you reach one minute or until the reaction completes, as evidenced by the cessation of bubbling.
12. When the reaction completes, record the final mass of the cup, water, and tablet on Line Q of Table.
13. Dispose of the spent solution and rinse out the cup.
14. Repeat steps 6 through 9, using 2 M hydrochloric acid.
15. Repeat steps 6 through 9, using 1 M hydrochloric acid.

Table: Effect of concentration on reaction rate – observed and calculated data

Item	Trial A (4 M HCI)	Trial B (2 M HCI)	Trial C (1 M HCI)
A. mass of tablet	___.__g	___.__g	___.__g
B. mass of cup + hydrochloric acid	___.__g	___.__g	___.__g
C. temperature of hydrochloric acid	___.__°C	___.__°C	___.__°C
D. mass at 0:00 (A + B)	___.__g	___.__g	___.__g
E. mass at 0:05	___.__g	___.__g	___.__g
F: mass at 0:10	___.__g	___.__g	___.__g
G: mass at 0:15	___.__g	___.__g	___.__g
H: mass at 0:20	___.__g	___.__g	___.__g
I: mass at 0:25	___.__g	___.__g	___.__g
J: mass at 0:30	___.__g	___.__g	___.__g
K: mass at 0:35	___.__g	___.__g	___.__g
L: mass at 0:40	___.__g	___.__g	___.__g
M: mass at 0:45	___.__g	___.__g	___.__g
N: mass at 0:50	___.__g	___.__g	___.__g
O: mass at 0:55	___.__g	___.__g	___.__g
P: mass at 1:00	___.__g	___.__g	___.__g
Q: mass at completion of reaction	___.__g	___.__g	___.__g
R: mass loss (D – Q)	___.__g	___.__g	___.__g
S: mass loss percentage [(R/A)·100]	___.__%	___.__%	___.__%

Safety Procedures:

1.   Always add acid to water. Adding water to a concentrated acid can cause splattering.

      2. Diluting acid produces heat. Because we want concentration to be the only variable, it’s important to ensure that all three acid solutions are at the same initial temperature.

3. Make your dilute acid solutions ahead of time and allow all three cups to cool to room temperature before proceeding.