IN COLLECTION

Lab: Periodic Trends

By now you should have a fairly good idea of what happens to the atomic size, ionization energy, and electron affinity as you move around the periodic table.  Ultimately, you should be able to use this knowledge to predict the relative reactivity of different substances.  The lab today will challenge your prediction skills.

We will be considering three substances today:  Potassium, Calcium, and Zinc.  We are trying to determine which of these substances is most reactive when combined with water.  You will need to decide how you will determine what is most and what is least reactive and take data and observations accordingly.

PLEASE HAVE YOUR GOGGLES ON AT ALL TIMES!!!

Begin the lab by washing all of the glassware.  You should have 3 Erlenmeyer Flasks (at least 500mL), a pair of forceps, 3 pieces of pH tape and a pair of flame resistant gloves.

Once your glassware is clean, fill each flask with 200mL of water. 

Select a person to garner the chemicals.  Make sure that you record the mass of each substance.  Get only 1 substance at a time.  Obtain the substance, test the reactivity, dispose of the waste, and obtain the next substance.  Please wait for your teacher to give you the OK before getting the potassium.

GARNERING THE SUBSTANCES

  • Use a coffee filter to gather approximately 10 small pieces of zinc
  • Use DRY tongs to get one piece of calcium, place it on a coffee filter on the scale
  • Use DRY tongs to get one piece of potassium, place it on a coffee filter on the scale

 

SUBSTANCE

MASS OF SUBSTANCE (g)

Zinc

 

 

Calcium

 

 

Potassium

 

 


TESTING THE REACTION

  • During all reactions, gently place substance into the water and immediately stand back
  • Don’t forget to record qualitative and quantitative observations (i.e. time)
  • QUICKLY STAND BACK TO WAIT FOR REACTION
  • If no reaction happens after a minute, gently swirl the container.  When doing this, please make sure that you have the flame resistant glove on.  If a reaction happens, carefully but quickly, step back
  • Never look directly over the top of the flask!


TESTING pH

  • Don’t forget to test the pH.  If the paper turns red, you have an acid…if it is blue you have a base.


DISPOSAL

  • Zinc Reaction—dump water down the drain (no solids!!!) and place any solids in the beaker under the fume hood
  • Calcium Reaction—dump all wastes into the disposal container under the fume hood
  • Potassium Reaction—dump all wastes in the disposal container under the fume hood


You will be graded on both a lab write up (using the lab report rubric) and the following questions.

PRE-LAB WORK:
1)    What is the problem/question of this lab?


2)    What is your hypothesis?  Make sure that your hypothesis is testable (i.e. how will you determine which is most reactive…time? …precipitate formed?…relative difference in color?…heat produced?



3)    Justify your hypothesis using all that you know about chemistry so far.  Please be thorough.




Questions to consider for the lab—Include as Appendix A in your Lab Report (4pts each)

1)    How do you know when a chemical reaction has taken place?



2)    Write the electron configuration for each of the following metals (you may use the shortcut):

K: ____________________________________________________________________________
Ca: ___________________________________________________________________________
Zn: ___________________________________________________________________________

3.    Why do you think that the Potassium must be stored under mineral oil?


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