2 Chemical tests Flashcards
How do you test for hydrogen?
A lighted splint is held to the mouth of the tube. The hydrogen explodes with a squeaky pop.
How does hydrogen combine with oxygen?
Explosively.
What is the equation for hydrogen reacting with oxygen?
2H2 + O2 —> 2H2O
How do you test for oxygen?
A glowing splint is put into the tube containing the gas. Oxygen relights a glowing splint.
How can you test for carbon dioxide gas?
The carbon dioxide is bubbled through limewater. Carbon dioxide turns limewater milky/chalky/cloudy.
What is another word for limewater?
Calcium hydroxide.
What does limewater (calcium hydroxide solution) react with carbon dioxide to form?
A white precipitate of calcium carbonate.
What is an equation that represents limewater reacting with carbon dioxide?
Ca(OH)2 + CO2 —> CaCO3 + H2O
How do you test for chlorine gas?
A piece of damp litmus paper or universal indicator paper is put into the test-tube or held over its mouth.
What does chlorine gas do to the indicators?
Chlorine is a green gas that bleaches (turns white) the damp litmus paper or universal indicator.
What exactly happens to these papers?
If blue litmus paper or universal indicator paper are used for this test, they go red first (the chlorine dissolves in the water to form an acid solution) and then white.
How can you test for ammonia gas?
Hold a piece of damp universal indicator or red litmus paper at the mouth of the test tube.
What does ammonia do to the universal indicator paper/litmus paper?
It turns it blue.
What is special about ammonia?
It is the only alkaline gas that we will come across in this syllabus.
How could we test for water?
With anhydrous copper sulfate a it turns it blue.
How can we tell that there is water?
Anhydrous copper sulfate lacks water of crystallisation and is white. Dropping water onto it replaces the water of crystallisation and turns it blue.
What is the word equation for the anhydrous copper sulfate?
Anhydrous copper sulfate + water —> Hydrated copper sulfate.
What could this test also be done on?
Anything that contains water, so it would work with sodium chloride solution or sulfuric acid. It does NOT show that the water is pure.
How can you find out if water is pure?
By measuring the freezing (melting) point or boiling point.
How could you use the freezing or boiling point to show purity?
Pure water freezes at exactly 0C and boils are exactly 100 at 1 atmospheric pressure.
How could we use this information for impurities?
If the water is impure, it will usually freeze at a lower temperature and boil at a higher temperature.
What do all salts have in relation to ions?
One cation and one anion.
What is a cation?
A positive ion.
What is an anion?
A negative ion.
What do flame tests show?
The presence of certain metal ions - cations - in a compound.
What is step 1 of the procedure for flame tests?
A platinum or nichrome wire is dipped into concentrated hydrochloric acid.
What is step 2 of the procedure for flame tests?
And then into the salt you want to test, so that some salt sticks on the end.
What is step 3 of the procedure for flame tests?
The wire and the salt are then held just within a roaring bunsen burner and their colours are observed.