Chemical Tests Flashcards
What is qualitative analysis
Qualitative analysis is the process of performing chemical tests on unknown compounds to determine their identity. These include tests for cations and anions
Describe the process of a flame test
Dip the tip of a platinum wire into concentrated hydrochloric acid and then in the flame of a bunsen burner in order to clean it and ensure that it doesn’t color the flame from previous tests. Once clean, the wire is dipped again in acid and used to pick up a few crystals of the compound to be tested. When the wire is held at the end of a blue, non-luminous flame, a new color in the flame will appear
What color does the lithium cation (Li+) produce
Red
What color does the sodium cation (Na+) produce
Orange
What color does the potassium cation (K+) produce
Lilac
What color does the calcium cation (Ca2+) produce
Orange red
What color does the copper cation (Cu2+) produce
Green
Why should the platinum wire be cleaned first before using it for the flame test
To avoid contamination and ensure that the wire won’t color the flame from previous tests
Why is a non-luminous flame used
A non-luminous flame is used to clearly see the color of the cation. The yellow color of the luminous flame would mask the color and visibility of the flame color of the test sample
What are the two possible tests for cations and which cations are they for
Flame test: Lithium, Sodium, Potassium, Calcium, Copper(II)
Adding sodium hydroxide solution: Copper(II), Iron(II), Iron(III)
Describe the process of adding sodium hydroxide to identify a cation
Add aqueous sodium hydroxide solution dropwise and then in excess to an aqueous solution containing a metal cation. This will produce a metal hydroxide. Since most metal hydroxides are insoluble, the color of the insoluble precipitate can be used to identify the cation
What color is the precipitate produced when adding sodium hydroxide to copper(II) cations
Blue
What color is the precipitate produced when adding sodium hydroxide to copper(II) cations
Blue
What color is the precipitate produced when adding sodium hydroxide to iron(II) cations
Green
What color is the precipitate produced when adding sodium hydroxide to iron(III) cations
Yellow/orange