SAMPLE ALKASELTZER LAB NAMES & WORK WITH A PARTNER

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Sample Alka-Seltzer Lab Names &

work with a partner, hand in one write-up per pair


What affects the rate of a reaction?


Introduction:


In this lab, you will work with a partner to investigate what factors affect the RATE of a chemical reaction. When an Alka-Seltzer tablet is put into water, there is a reaction.


The reaction, however, is NOT between the chemicals in the Alka-Seltzer and the water. The reactants are actually both found in the solid tablet. The water assists in loosening the reactants so that they can move around, collide, and form the products.


One of the products is a gas, which is why we hear fizzing when the tablets are put into water. The ingredients (reactants) of this reaction are CITRIC ACID (H3C6H5O7) and SODIUM BICARBONATE (NaHCO3). These compounds are unable to react when in a solid state. When the tablet is placed in water, the compounds ionize, allowing them to react.


The balanced reaction is:

SAMPLE ALKASELTZER LAB NAMES & WORK WITH A PARTNER H­3­C­6­H­­5O­7­­ (aq) + 3 NaHCO­3 (aq) Na­3­C­6­H­5­O­7­ (aq) + 3 H­2­O (l) + 3CO­2­ (g)


In this lab, you will design experiments to determine TWO concepts:


-how temperature affects the rate of reaction

-how surface area affects the rate of reaction


For EACH part, you will have to:

  1. State a hypothesis (This should be an “If……then….” statement.)

  2. Perform the experiment, and collect data.

  3. After performing the lab, draw a conclusion.



PART ONE: Effect of temperature on a chemical reaction.

HYPOTHESIS (How will temperature affect the rate of a chemical reaction?)

An Alka-Seltzer tablet will dissolve faster in hot water than in cold water.



PROCEDURE (NUMBER YOUR STEPS)

  1. Place an Alka-Seltzer tablet on a piece of paper towel.

  2. Break the tablet in two with a spatula.

  3. Weigh each piece using an electronic balance. Adjust the weight of one piece by breaking off fragments with the spatula so that the masses of each piece are identical. Record the mass of each piece of tablet.

  4. Using a graduated cylinder, measure 50 mL of hot tap water into a 100 mL beaker and measure 50 mL of cold tap water into another 100 mL beaker. Verify the temperatures are different using an electronic thermometer. Record the temperatures of each beaker of water.

  5. Simultaneously add one piece of tablet to each beaker of water.

  6. Observe and note which tablet, if any, dissolves first.



What is the independent variable in this experiment? ______temperature_____________



What is the dependent variable in this experiment? ________time___________________



DATA: (SET UP A DATA TABLE – ROW/COLUMN)



mass of piece of tablet/ g

volume of water/ mL

temperature of water/ oC

time to finish dissolving

time to finish dissolving/ min:s

1.6

50

22.7

second

1:53

1.6

50

48.5

first

1:07



Note you only need one time column: either compare which finishes first or second, or record real times.



CONCLUSION (Was your hypothesis correct? How do you know?)

My hypothesis was correct: the hot water dissolved the piece of tablet faster than cold water. I ensured the only variable was temperature, all other factors were kept constant (mass of piece of tablet, volume of water, identical beakers for each experiment).





If you had more time, what additional procedures could you follow?

  1. Use whole tablets instead of breaking a tablet into pieces. The masses would be the same. There would be no variations in shape or surface area which might slightly affect results as in this experiment.

  2. Use a more accurate balance (2 decimal places).




Explain WHY temperature affects the rate of a chemical reaction

At higher temperatures, the reactant particles in the Alka-Seltzer have more energy and so move faster and therefore collide more often. More collisions result in an increased rate of reaction.









PART TWO: Effect of surface area on a chemical reaction.

HYPOTHESIS (How will surface area affect the rate of a chemical reaction?):

A crushed Alka-Seltzer tablet has a greater surface area than a whole tablet, and will dissolve more quickly in an equal volume of water at the same temperature as a whole tablet.





PROCEDURE (NUMBER YOUR STEPS)

  1. Place an Alka-Seltzer tablet on a piece of paper towel.

  2. Break the tablet in two with a spatula.

  3. Using an electronic balance, record the mass of the smaller piece of tablet.

  4. Using a pestle and mortar, grind the larger piece of tablet into smaller pieces. Weigh out an equal mass of this ground piece of tablet as the piece in 3.

  5. Using a graduated cylinder, measure 50 mL of tap water into two 100 mL beakers. The temperature of water in each beaker of water is the same and can be verified with an electronic thermometer.

  6. Simultaneously add the piece of tablet from 3 and the ground tablet from 4 to each beaker of water.

  7. Observe and note in which beaker, if any, the Alka-Seltzer dissolves first.





What is the independent variable in this experiment? ____surface area of Alka-Seltzer_________



What is the dependent variable in this experiment? _____time_________________________



DATA: (SET UP A DATA TABLE – ROW/COLUMN)



surface area of Alka-Seltzer

mass of piece of tablet/ g

volume of water/ mL

time to finish dissolving

time to finish dissolving/ min:s

low - chunk

1.6

50

second

1:55

high - ground

1.6

50

first

0:47



Note you only need one time column: either compare which finishes first or second, or record real times.



CONCLUSION (Was your hypothesis correct? How do you know?)

My hypothesis was correct: the ground Alka-Seltzer with the higher surface area dissolved more quickly than an equal mass of Alka-Seltzer in a single chunk. I ensured the only variable was surface area; all other factors were kept constant (mass of piece of tablet, volume of water, identical beakers for each experiment, temperature of water).



If you had more time, what additional procedures could you follow?

  1. Use whole tablets initially. The masses would be the same. Then you could grind a whole tablet and transfer all of it to the reaction.

  2. Use a more accurate balance (2 decimal places).

  3. If the Alka-Seltzer is too finely ground I observed that it floats! I would perform another experiment where, instead of grinding it, I instead break into many small pieces with a spatula.



Explain WHY surface area affects the rate of a chemical reaction

Grinding or breaking an Alka-Seltzer tablet increases the number of particles and increases the surface area. Material which was within the tablet is exposed, allowing for more collisions between reactant particles and resulting in an increased rate of reaction.




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