Chemical tests Flashcards
tests for anions and cations produce 5 gases
- ammonia
- carbon dioxide
- oxygen
- chlorine
- hydrogen
ammonia turns damp red litmus paper what colour
blue
how to test for ammonia
have a test tube with the solution over a bunsen burner
hold litmus paper at the tip of the test tube but don’t touch the sides
the red litmus paper should turn blue
what is the reaction for the test for carbon dioxide
limewater turns cloudy
test for carbon dioxide
The test for carbon dioxide involves bubbling the gas through an aqueous solution of limewater
test for chlorine gas
- handle in a fume cupboard as it is toxic
- put some damp blue litmus paper to the test tube and it should turn red and then bleach white
why does damp blue litmus paper turn red at the beginning for chlorine
as acids are produced when chlorine comes into contact with water
chlorine has a sharp characteristic, what is it
the smell
colour change for chlorine
from damp blue litmus paper to red and then to white
Test for hydrogen gas
consists of holding a burning splint at the open end of a test tube of gas
If the gas is hydrogen it burns with a loud “squeaky pop”
Be sure not to insert the splint right into the tube, just at the mouth, as the gas needs air to burn
why is there a squeaky pop for hydrogen
its the result of the rapid combustion of hydrogen with oxygen to produce water
test for oxygen
place a glowing splint inside a test tube of gas
If the gas is oxygen, the splint will relight
how do you tell the test for hydrogen and oxygen apart
Try to remember that a ligHted splint has an H for Hydrogen, while a glOwing splint has an O for Oxygen.
how do you carry out a flame test
- dip the loop of a wire in dilute hydrochloric acid
- then place it into a blue flame which decontaminates it
- then place it in a solid sample containing metal ions
- place it back into a blue flame
a colour change should appear
lithium ions produce what colour flame
RED
Potassium ions produce what colour flame
LILAC
Sodium ions produce what colour flame
YELLOW
Copper ions produce what colour flame
Blue- green
Calcium ions produce what colour flames
orange- red
Metal cations in aqueous solution can be identified by what
the colour of the precipitate they form on addition of sodium hydroxide
the metal ion copper forms what precipitate when adding Sodium hydroxide
light blue precipitate formed
the metal ion Iron II forms what precipitate when adding Sodium hydroxide
Green precipitate formed
the metal ion Iron III forms what precipitate when adding Sodium hydroxide
brown precipitate formed
effect of adding sodium hydroxide
to ammonium
Ammonia gas is produced which turns damp red litmus paper blue
anions are what
negatively charged ions
carbonate contains what ions
CO₃²⁻
what is the test for carbonate ions ( anion)
- add dilute hydrochloric acid
- bubble carbon dioxide gas through limewater
- if carbonate ions are present then limewater will turn cloudy and effervescence will happen
sulfates contain
SO₄²⁻
test for sulfate ions (anion)
- add dilute nitric acid to a test tube
- add aqueous barium nitrate
- a white precipitate should form ( of barium sulphate)
halide ions are
ions formed by group 7 elements when they gain an electron
halide ions include
Chloride
Bromide
Iodide
test for halide ions ( Anion)
- add dilute nitric acid
- add silver nitrate solution
- different precipitates should form of the silver halide
what precipitate would silver chloride form for the halide ion test
white
what precipitate would silver bromide form for the halide ion test
cream
what precipitate would silver iodide form for the halide ion test
yellow
water can be identified using 2 tests, what are they
a physical one and a chemical one
chemical test for water
Anhydrous copper(II) sulfate turns from white to blue on the addition of water
physical test for water
check its boiling point
A sample of the liquid is placed in a suitable container such as a boiling tube and gently heated
Using a thermometer, you can check if the boiling point is exactly 100 oC
Any impurities present will usually tend to raise the boiling point and depress the melting point of pure substance
