Here is the continuation of the salt analysis done by a student (Grade 8), after having gone through the ENV model to identify different variables encountered in a salt.

Unknown Salt



We are going to test an unknown salt to find its basic and acid radical. We are going to go through a series of tests to accomplish this.

Hypothesis We can test the salt in a few different ways, such as: Flame test and Precipitation test. These different types of experiments will give different, and (maybe some) similar results.

Apparatus Safety gear (Safety goggles and lab apron), test tubes, spatula, pipette, Bunsen burner, platinum/nichrom wires, matches/lighter, starch Iodine paper, test tube holders and Petri dishes.

Reagents Na OH, HCL, Distilled water and lime water.


Gas test:

1)      Put the salt in a dry and clean test tube.

2)      Hold the test tube (with test tube holders) over a Bunsen burner.

3)      Now you can do any of these four tests:

a)      Put a glowing match into the test tube , if it rekindles the substance has oxygen in it

b)      Do the same as A), instead of the match rekindling, a thick brown gas comes out. If this happens the substance has [k1] Nitrogen Dioxide.

c)       Now don’t do any of the actions in A) or B). Instead you just hold the test tube (with test tube holders) over the Bunsen burner and hold a Starch-Iodine-Paper over the gas outlet. If the paper turns blue it contains Chloride.

d)   Pour lime water into the test tube, if it turns cloudy the substance contains Carbon Dioxide. [k2]


Flame test:

1)      Squirt HCL onto the salt (with a pipette, into a Petri dish)

2)      Let the HCL dissolve all the salt, and use a platinum/nichrom wire to hold the salt (with HCL) over the Bunsen burner.

3)      Observing the color you can tell what the basic radical in the salt is.

Precipitation test:

1)      Take a small spatula of salt into a test tube

2)      Squirt distilled water into the test tube, put a cork on the test tube and shake it.

3)      Take off the cork and add Na-OH observe the color and by the color you can tell what basic radical the substance is




Gas test: In the gas test we found out that the salt contained Nitrogen[k3] , because the gas was brown. (Chemical Equation: Fe (NO3)3 (Heatà) Fe+3NO3[k4] )

Precipitation test: In the PPC test the liquid [k5] was also brown, telling us that the salt contained Ferric. (Chemical Equation: Fe (NO3)3+3NaOH -à Fe (OH) 3+3NaNO3)

Altogether this told us that the salt was Ferric Nitrate.


[k1]Is giving out

[k2]Pass the gas that is coming out through lime water, not pour lime water into the test tube1


[k4]Look up the chemical reaction!

[k5]Precipitate was brown


# Alexander Sokol 2011-05-28 16:25
Krishna, can you please elaborate a little on how you see teaching thinking in this particular part of the lesson? It'd be great if you could connect it to the framework and follow the structure of the post we agreed on.
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