Testing for Cations

Edited by Jamie (ScienceAid Editor)

Flame Test

A flame test can be used where a compound is put under a flame. The procedure is as follows:

  1. 1
    Heat the nichrome wire.
    Was this step helpful? Yes | No | I need help

  2. 2
    Dip it in the hydrochloric acid.
    Was this step helpful? Yes | No | I need help

  3. 3
    Dip the wire into the compound you are testing so a small blob is collects on the wire.
    Was this step helpful? Yes | No | I need help

  4. 4
    Put the tip of the wire into a flame and see what color it turns.
    Was this step helpful? Yes | No | I need help

how to carry out the flame test

These are the colors you will see for different ions:

Ion Color
Sodium (Na+) Orange-yellow
Potassium (K+) Lilac
Calcium (Ca2+) Brick-red
Copper (Cu2+) Green

Sodium Hydroxide Test for Cations

Add several drops of sodium hydroxide (NaOH) solution to the solution being tested. If a coloured precipitate is formed then stop and find out what the cation is. If a white precipitate forms then continue to add NaOH to it and observe whether the precipitate dissolves.

Was this helpful? Yes | No | I need help

Cation Precipitate color Further results
Aluminium (Al3+) White Precipitate dissolves as more NaOH is added to the solution
Calcium (Ca2+) White Precipitate will not dissolve in the NaOH solution
Copper (Cu2+) Pale blue none
Iron(II) (Fe2+) Pale green none
Iron(III) (Fe3+) Red-brown none

The ionic equation for these reactions are all very similar, here is an example it with Aluminium:

Al3+(aq) + 3OH- ==>> Al(OH)3(s)

All you have to do for any other ionic equations for this test is to change the number of OH- ions so that it balances with the oxidation state of the metal anion. E.g. Iron (II) would need two OH- whereas Iron(III) needs 3.

Was this helpful? Yes | No | I need help

Questions and Answers

Why do cations form and how do we tell by the color?

How do we know by the color of the precipitate for which cation it is, is it the bonds

ScienceAid QnA. This section is not written yet. Want to join in? Click EDIT to write this answer.

I am looking for the Cation test which uses HCL, are you able to tell me what it is?

Hi Jamie,. . I am looking for the Cation test which uses HCL, are you able to tell me what it is?. Thanks. . It will help a bunch

ScienceAid QnA. This section is not written yet. Want to join in? Click EDIT to write this answer.

Comments

ScienceAid welcomes all comments. If you do not want to be anonymous, register or log in. It is free.




Jamie
Featured Author
166 Articles Started
1,271 Article Edits
43,065 Points
Jamie is a featured author with ScienceAid. Jamie has achieved the level of "Captain" with 43,065 points. Jamie has started 166 articles (including this one) and has also made 1,271 article edits. 43,400 people have read Jamie's article contributions.
Jamie's Message Board
Jamie: Hi, my name is Jamie.
Jamie: Can I help you with your problem about "Testing for Cations"?
 

Article Info

Categories : Applied

Share this Article:

Thanks to all authors for creating a page that has been read 3,051 times.

Do you have a question not answered in this article?
Click here to ask one of the writers of this article
x

Thank Our Volunteer Authors.

Would you like to give back to the community by fixing a spelling mistake? Yes | No