chemical tests

Question 1

what is the test for hydrogen gas

Answer 1

Test for Hydrogen Gas:
A lighted splint is held near the mouth of a test tube containing Hydrogen gas
A squeaky pop is heard –> this is the hydrogen gas exploding

Question 2

what is the equation when you test for hydrogen gas

Answer 2

2H2 + O2 –> 2H2O(l)

Question 3

what is the test for oxygen gas

Answer 3

Test for Oxygen Gas:
A glowing splint is put into a test tube containing oxygen gas
You see the splint relight

Question 4

what is the test for co2

Answer 4

Test for CO2:
CO2 gas is bubbled through limewater
Limewater becomes cloudy/milky/chalky
Limewater = Ca(OH)2 solution

Question 5

what happens when you continue bubling co2 when the precipitate caco3 is in the co2 test

Answer 5

When you bubble CO2 through limewater, it forms the precipitate CaCO3
If you continue bubbling CO2 through, the precipitate disappears as the CO2 reacts with the CaCO3, to form calcium hydrogencarbonate which is soluble

Question 6

what is the equation for caco3 + co2 when you continue bubbling co2 in the co2 test

Answer 6

Ca(OH)2+ CO2 –> CaCO3 + H2O

Question 7

what is the equation when you test for co2

Answer 7

CaCO3+H2O+CO2–> Ca(HCO3)2

Question 8

what is the test for chlorine gas

Answer 8

Test for Cl2:
Put a piece of damp litmus paper or universal indicator paper into a test tube
Chlorine is a green gas
Chlorines bleaches damp litmus paper or universal indicator paper
Chlorine will turn the litmus paper red and then white, as it first dissolves to form an acidic solution
Tip to remember: Chlorine is used in swimming pools - this is to keep the pool clean - bleach is also something used to keep things clean - so remember chlorine BLEACHES damp litmus paper

Question 9

what is the test for ammonia gas

Answer 9

test for Ammonia Gas:
Hold a piece of damp litmus paper or universal indicator - when it turns blue you know it is ammonia gas
It is the only alkaline gas you learn at iGCSE

Question 10

what is the test for water

Answer 10

Test for Water:
Water turns white anhydrous copper sulfate into blue hydrous copper sulfate
When adding water, you see a colour change from white to blue

Question 11

what is the equation when you test for water

Answer 11

CuSO4 + 5H2O –> CuSO4.5H2O

Question 12

Test for Pure Water

Answer 12

When a substance is impure, its MP/BP changes
With water, to test if it is pure, you boil or freeze it
If it is impure, it will freeze at a lower temperature and boil at a higher temperature

Question 13

write the methods for the test for cations

Answer 13

Test for Cations(metals) in Salts because all cations are metals in salts:
A platinum or nichrome wire is dipped into concentrated hydrochloric acid, and then the salt (to make sure the salt sticks onto the wire)
The wire with the salt on it is held in a non-luminous flame (roaring) in the bunsen burner –> (blue flame)
Between each new salt (each new metal) it is ideal to use a new wire
If a new wire is not being used, you dip the wire into concentrated hydrochloric acid, and hold it in the non-luminous roaring flame, and you repeat this until no colour is produced

Question 14

when burned, what is the color of lithium

Answer 14

Lithium - crimson red

Question 15

when burned, what is the color of sodium

Answer 15

Sodium - yellow (sometimes looks like orange

Question 16

when burned, what is the color of potassium

Answer 16

Potassium - lilac flame

Question 17

when burned, what is the color of calcium

Answer 17

Calcium - orange-red

Question 18

when burned, what is the color of copper

Answer 18

Copper (II) - blue-green

Question 19

what must you keep in mind when testing for lithium

Answer 19

Strontium gives a similar colour to lithium (red) - the only way to differentiate is to compare a metal you KNOW is lithium and compare the redness of that flame with the metal you are testing

Question 20

which elements are the only soluble ones when testing for cations using sodium hydroxide

Answer 20

Testing for Cations using Sodium Hydroxide
Ammonium, potassium and sodium hydroxide are the only soluble ones (APS).

Question 21

how do you test for cations using sodium hydroxide

Answer 21

To carry out this test:
Dissolve the salt in distilled water (distilled=pure water)
Add 1cm^3 to a test tube
Add 1cm^3 of diluted sodium hydroxide solution
Look for a precipitate to form (this might mean that the solution goes cloudy)

Question 22

what happens when you add NaOH to a solutuon containing other metla ions

Answer 22

When you add sodium hydroxide to a solution containing other metal ions, a precipitate is formed with that metal (metal hydroxide)

Question 23

what is the test for iron (iii)

Answer 23

Test for Iron (III) ions:
An Fe (III) hydroxide precipitate is an orange-brown colour
FeCl3(aq)+3NaOH–> Fe(OH)3(s) + 3NaCl –> full equation
Fe3+ (aq) + 3OH- (aq) –> Fe(OH)3(s) –> ionic equation

Question 24

write the full and ionic equation when testing for iron (III) ions

Answer 24

FeCl3(aq)+3NaOH–> Fe(OH)3(s) + 3NaCl –> full equation
Fe3+ (aq) + 3OH- (aq) –> Fe(OH)3(s) –> ionic equation

Question 25

what is the test for copper (II)

Answer 25

Test for Copper (II) ions:
Copper hydroxide precipitate is a blue colour
CuSO4 (aq) + 2NaOH(aq) –> Cu(OH)2(s) + Na2SO4(aq)
Cu2+(aq)+2OH-(aq)–>Cu(OH)2(s)

Question 26

write the full and ionic equation when testing for copper (II) ions

Answer 26

CuSO4 (aq) + 2NaOH(aq) –> Cu(OH)2(s) + Na2SO4(aq)
Cu2+(aq)+2OH-(aq)–>Cu(OH)2(s)

Question 27

test for iron (II)

Answer 27

Test for Iron (II) Ions:
Iron(II) hydroxide precipitate is a green colour
FeSO4(aq) + NaOH(aq)–> Cu(OH)2(s) + Na2SO4(aq)
Fe2+(aq) + 2OH-(aq) –> Fe(OH)2(s)

Question 28

write the full and ionic equation when testing for iron (II) ions

Answer 28

FeSO4(aq) + NaOH(aq)–> Cu(OH)2(s) + Na2SO4(aq)
Fe2+(aq) + 2OH-(aq) –> Fe(OH)2(s)

Question 29

when you test for iron (II) why does the green precipitate become orange brown

Answer 29

When the test tube is left standing, the green precipitate becomes orange-brown precipitate. This is because the Fe(II) hydroxide is oxidised by the air, so becomes Fe(III) hydroxid