2.8- Chemical test

Question 1

What is the test for hydrogen?

Answer 1

-To test for hydrogen, remove the bung and insert a burning splint. Hydrogen gas produces rapidly and produces a pop sound. The hydrogen combines explosively with the oxygen in the air to make water.

Question 2

What is the test for oxygen?

Answer 2

-To test for oxygen use a glowing splint put into a tube containing the gas. Oxygen relights a glowing splint.

Question 3

What is the test for carbon dioxide?

Answer 3

-To test for carbon dioxide bubbled through limewater. Carbon dioxide turns limewater milky/chalky/cloudy
-Limewater is calcium hydroxide solution. Carbon dioxide reacts with it to form a white precipitate of calcium carbonate

Question 4

What is the test for chlorine

Answer 4

-A piece of damp litmus paper or universal indicator paper is put into the test tube o held over its mouth. Chlorine is a green gas that bleaches the damp litmus paper or universal indicator paper.
-If blue litmus paper or universal indicator paper are used for this test, they go red first the chlorine dissolves first and then turns white

Question 5

What is the test to show water is pure?

Answer 5

-You can find out whether a sample of water is pure by measuring the freezing melting or boiling point. Pure water freezes at exactly 0 c and boils at exactly 100 c. If the water is impure it will usually freeze at a lower tempreture and boil at a higher tempreture.

Question 6

What do all salts contain?

Answer 6

-All salts contain at least one cation (positive ion) and anion (negative ion).

Question 7

Explain the flame test

Answer 7

-A flame test is used to show the presence of certain metal ions (cations) in a compound. A platinum wire is dipped into concentrated hydrochloric acid and then into salt, some of the salt has to stick onto the end. The wire and the salt are then held just within a roaring Bunsen burner flame and the colours observed.

Question 8

What colour does Lithium turn in hydrochloric acid?

Answer 8

-Lithium produces a red or crimson flame

Question 9

What colour does sodium turn in hydrochloric acid

Answer 9

-Sodium produces a yellow flame

Question 10

What colour does potassium turn in hydrochloric acid

Answer 10

-Potassium produces a lilac flame

Question 11

What colour does calcium turn in hydrochloric acid

Answer 11

-Calcium produces a orange-red flame

Question 12

What colour does copper turn in hydrochloric acid

Answer 12

-Copper ion produces a green flame

Question 13

What is the problem of the flame test?

Answer 13

The colour of the flame can be difficult to distinguish that is especially true if there is a low concentration of the metal compound. Sometimes a sample ion contains a mixture of metal ions can mask the colour of the flame

Question 14

How to test for cations?

Answer 14

of the common Hydroxides only sodium potassium and ammonium hydroxides dissolve in water to any extent. Most metal hydroxides are insoluble. This means that if you add sodium hydroxide solution to a solution containing the metal ions, you will get a precipitate of the metal hydroxide. To carry out this test dissolve the salt in distilled pure water and put about 1cm3 in a test-tube. Add about the same volume of dilute sodium hydroxide solution. In these solutions the formations precipitate the solution will go cloudy. As a solid forms

Question 15

What is the test for copper (II) ions

Answer 15

Copper II ions react with sodium hydroxide to form a blue precipitate of copper (II) hydroxide. Any copper (ii salt solution will react with sodium hydroxide solution in this way copper(II) hydroxide

Question 16

What is the test for Iron (III) Ions

Answer 16

Iron (III) ions react with sodium hydroxide to form a brown precipitate of iron (III) hydroxide

Question 17

What is the test for Iron (II) Ions?

Answer 17

Iron (II) ions react with sodium hydroxide to form a green precipitate of Iron(II) hydroxide.

Question 18

What is the test for Ammonium ions?

Answer 18

When ammonium salts react with sodium hydroxide solution they react together to produce ammonia gas. No fizzing because ammonia is highly soluble in water and immediately goes into solution. So it is placed in a warm test tube and the ammonia is released from the solution back to a gas. Ammonia can be detected by placing a piece of damp red litmus paper near the mouth of the test tube. Ammonia dissolves in the water on the litmus paper forming an alkaline solution. This turns the litmus paper blue.

Question 19

What is the test for carbonate ion?

Answer 19

Carbonate ions react withhydrochloric acid to form the gas carbon dioxide. Adding little dilute hydrochloric acid to a sample of the salt and fizzing should occour, this should show that the reaction is giving of a gas. To test the gas bubble it through limewater to show that it is carbon dioxide. Carbon dioxide reacts with calcium hydroxide to form calcium carbonate. The Calcium carbonate forms a white precipitate turning the limewater cloudy. Most carbonates are insoluble in water so this test will use a sample of a solid.

Question 20

What is the test for sulfate ions?

Answer 20

Makea solution of the suspected sulfate in distilled water and add some dilute hydrochloric acid and add some barium chloride solution. A sulfate will produce a while precepitste of barium chloride.

Question 21

What are the test for chlorides and bromides?

Answer 21

Add enough dilute nitric acid to make it acidic. Then add some silver nitrate solution.
A white precipitate of silver chloride shows the presence of chloride ions.
A cream precipitate of silver bromide shows the presence of bromide ions
A yellow precipitate of silver iodide shows the presence of iodide ions