Separation and Qualitative Determination of Cations and Anions
Introduction and Help Sheet
“Lab Bible”
In this qualitative lab, you will be using chemical reactions to determine the presence of ions in solution.
First, you will practice with a solution that is known to contain the ion and then test an unknown solution to see
which of the possible ions it contains. After the “known” solution has been tested and the results carefully
recorded, obtain an “unknown” solution and repeat the process. By comparing your results you should be able
to determine which ions your solution contains. Your “unknown” must contain at least one of the ions, but it
could contain as many as ALL of the target ions.
Pre-Lab
1. First, carefully read through the Introduction, Background (READ THE LAST 2 SENTENCES
VERY CAREFULLY!!!), General Techniques for Qualitative Analysis (READ THIS WHOLE
SECTION VERY CAREFULLY!!!), and Safety Precautions sections of the lab.
2. Answer the pre-lab questions on the pre-lab sheet (they are different than the questions given in the
lab. The Background, General Technique, Experimental Overview, and Safety Precaution
sections will help with the general questions. The Procedure section (particularly what is in the
boxes) will be a huge help in answering the Testing and Reaction questions.
3. Read carefully through the procedure and fill out the Procedure column of the Data Table. KEEP
IT VERY BRIEF! Use abbreviations like “TT” for test tube, “PPT” for precipitate, “TA” for add till
acidic (+ HNO3 TA for add nitric acid until the solution is acidic), “TB” for add till basic, “TD” for
add till dissolves, “D” for drops, “HB” for heat in hot water bath, and “C” for centrifuge. Don’t
bother to include extra information that is not important for the procedure.
4. The pre-lab portion of the lab is due on 5/5!
Lab
Follow the directions in the lab very carefully. In order to get good results (and a good grade) you must
be thorough, precise, orderly, and neat!
 You will have only 10class days to complete the lab. The lab will be open before and after school
most days until the last day. Come in and work if you get behind. Your lab is due at the end of the
hour on 5/18. NO EXCEPTIONS!!!
 Only use small test tubes in the lab!
 The black labeled bottles are for the cation and the red labeled bottles are for the anions.
 Most of the acids and bases are in the fume hood.
 Use the pH paper sparingly (and distilled water and soap)! You can do many tests on one short strip.
Touch the stirring rod to the solution and then touch the paper. Make sure you check the color on the
chart – don’t just look for a color change! When adding until acidc/basic litmus paper is actually
easier because you will always get a color change!
 Use parafilm instead of rubber stoppers when shaking your mixture or storing it overnight.
 Store all solutions upright in a beaker!
 You will get 3 clean pipets at the start of the lab.
1) One Beral pipet (long thin stem) for mineral oil separation in Anion Step 2 (after doing the
known and unknown it will have to be thrown away)
2) One Beral pipet for collecting CO2 gas in Anion Step 3 and, after it is properly cleaned (see
below), for use again in Anion Step 5.
3) One graduated pipet (it has marks for 0.25, 0.5. 0.75, and 1 mL) for dispensing your
unknowns for all unknown parts of the lab (follow the directions found in the “Avoid
Contamination” section of the lab (page 2) for proper cleaning after each use).
 Reread the section on “Measuring Solutions”. Know approximately what 1 mL looks like in a small
test tube. Use the graduated pipet to put measure 1 mL of distilled water and place it in a small test
tube. That is what 1 mL looks like.
Using the Centrifuge
 The centrifuge is used in all liquid-solid separations in the lab and also whenever you are disposing a
liquid-solid mixture.
 Use the provided balancing test tubes and tap water to keep the centrifuge balanced while running.
 Liquid levels just need to be close – not exactly the same.
 Before centrifuging, always shake your solution vigorously to (1) cause any solids trapped by
surface tension on the top of the liquid to sink within the liquid and (2) mix any density bands (areas
of uniform density the resist mixing) that prevent the more dense solids from sinking to the bottom
of the test tube.
 Centrifuge directions:
1. Make sure the load is properly balanced
2. While keeping your hand on the knob, close the lid and lock it closed to start the centrifuge.
If the load is unbalanced, IMEDIATELY turn off the centrifuge. When the centrifuge has
stopped spinning (see the next step), check and redistribute the load. If you can’t identify the
problem, see the teacher for help.
3. If the centrifuge is properly balanced, let it spin for around 10 seconds. Turn the knob to turn
off the centrifuge, but keep the lid closed for another 10 seconds. Open the lid and place your
thumb on the round shiny nut to help the machine slow down to a stop.
Disposal
 Except for the mineral oil waste in Anion Step #2 ALL liquid waste solution can be carefully
decanted (pour down your stirring rod so the solid stays behind) down the drain, leaving the solid
portion behind in the test tube.
o How do you get the solid out of the test tube and into the appropriate waste beaker?
 Turn the test tube sideways and use the tap water squirt bottle to squirt water into the
test tube and flush the solid out into the waste beaker. 1 or 2 little squirts should be
enough to flush out most of the solid. DO NOT PUT THE SPOUT INTO THE TEST
TUBE OR YOU WILL COMTAMINATE THE BOTTLE.
 Cation waste goes in waste container #1
 Anion waste from steps 1, 4, and 5 goes in waste container #2, and anion waste
mineral oil from step 2 goes in waste container #3.
Deductions
 Every time I see you not disposing of waste properly, you will lose 1 point on your lab!
 You must clean up all spills appropriately and keep the lab area clean! When you leave the lab, your
station should be clean and DRY. Every time I see you not cleaning up after a spill or when you
leave the lab, you will lose 1 point on your lab!
 Replace the red tips on the bottle immediately! Every time I see you not replace the lid, you will
lose 1 point on your lab!
 Rule 2014 – Every small test tube broken will cost you a point on the lab!
 Every time I see you without goggles on, you lose 5 points!
 If you have to sit out the lab because you forgot “closed-toed shoes”, you lose 10 points!
 If you need more unknown, it will cost 5 points!
Common Errors and Tricky Steps
 When adding until acidic or basic, make sure to mix the solution thoroughly between testing for
acidity/basicity! THIS IS THE SINGLE MOST COMMON CAUSE OF MISTAKES IN THE LAB!
The best method of mixing involves wiggling your fingers to shake the test tube or covering the test
tube with parafilm and thoroughly shaking.
 Cation Step 3. Make sure the water is boiling and then leave it in at least 3 minutes! If you don’t,
you’ll pay for it in step 11!
o Did you get a blue solution in Step 9 or a brown precipitate in Cation Step 11 that ruins the
confirming test for Zinc? You did not get the water bath hot enough or heat the solution long
enough back in Step 3 and you didn’t precipitate out all of the copper and iron. You may
have also not added enough NaOH to precipitate all of the Cu2+/Fe3+ ions. YOU MUST
START OVER and do Step 3 correctly or you will never know if you have any zinc!
 Anion Step 5. One of the toughest tests to do properly without getting a false positive! Be very
careful adding the NaOH/unknown solution to the test tube – use the Beral pipet and release the
liquid down at the bottom of the test tube to make sure none of it touches the top third of the test
tube. Use a SMALL piece of cotton ball and push it half way down the tube. Finally, wet the red
litmus paper with DISTILLED water, fold over the top 1/4 and hang it in the top of the tube. (In the
Anion tray, use the paper clip with the hooked end to fish out the cotton ball and discard in the
trash.)
 Anion Step 3. Many people miss the cloudy precipitate and get a false negative. Hold the test tube
up to the light and give it a shake. Do you see ANY cloudiness?
Known Cations and Anions
o It doesn’t say it in the lab, but start with 10 drops of “known” cation solution to begin the cation
tests. The known ion solutions are in the larger bottle in appropriate tray.
o Don’t get rid of the liquid! You always save the liquid above the precipitate (called the supernatant)
for further testing until the very end of the cation lab.
Unknown Cations and Anions
o Obtain the “unknown” Cation and Anion (they are different samples!) from your teacher and record
the number in the Post-Lab Results Table.
o The sample contains 1-6 of the unknown ions.
o Shake the unknown to make sure it is uniformly mixed before starting any test.
o Be careful to use a CLEAN pipet when obtaining your 10 drops for testing so you don’t contaminate
your sample!
o Keep the unknowns safe! If you need more, it will cost you 5 points!
o Cations
 Look closely at it before you start the lab and read the beginning of the Part 1 Procedure very
carefully! (Especially read what is in the box!)
 Start with 10 drops of the unknown solution.
Cleaning and Returning Unknown Test Tubes
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Dump remaining solution down the drain
Rinse twice with tap water and then three times with distilled water
Return empty test tubes to teacher
Grades
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Qualitative Analysis Prelab: 30 points
Qualitative Analysis Lab: 200 points