Question

Say you are presented with two beakers, beaker A and beaker B, each containing a white, powdery compound.

a. From your initial observations, you suspect that the two beakers contain the same compound. Describe, in general terms, some experiments in a laboratory that you could do to help prove or disprove that the beakers contain the same compound.

b. Would it be easier to prove that the compounds are the same or to prove that they different? Explain your reasoning.

c. Which of the experiments that you listed above are the most convincing in determining whether the compounds are the same? Justify your answer.

d. A friend states that the best experiment for determining whether the compounds are the same is to see if they both dissolve in water. He proceeds to take 10.0 g of each compound and places them in separate beakers, each containing 100 mL of water. Both compounds completely dissolve. He then states,

Answer 1

a) You have to do the test using five sense-organs, i) physical appearance at glance, i.e. amorphous or crystalline or solid; color, ii) smell, iii) taste (if you are sure it's a normal salt), iv) sounding of molecule flow to ears v) contact by hand (If you are sure it's a normal salt)

After the test by sense-organs, if still not concluded, try to dissolve i) in water and see the observation ii) in dilute acid and see the observation iii) in the dilute base and see the observation.

b) Test by sense-organs is preferable only when the given compounds are simple salts, otherwise, it's better to try the solubility in water, acid or base.

c) Solubility test and checking the observation of precipitate formation (if any) and color change (if any) is the most acceptable/convincing method as they could be done without any risk.

d) Just by dissolving in water, it's difficult to decide whether they are the same or not. You should observe many things, like color change (or any other physical change). So you can't rely just on the solubility in equal amounts of water.

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