chemical tests Flashcards
what is the test for hydrogen gas
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
what is the equation when you test for hydrogen gas
2H2 + O2 –> 2H2O(l)
what is the test for oxygen gas
Test for Oxygen Gas:
A glowing splint is put into a test tube containing oxygen gas
You see the splint relight
what is the test for co2
Test for CO2:
CO2 gas is bubbled through limewater
Limewater becomes cloudy/milky/chalky
Limewater = Ca(OH)2 solution
what happens when you continue bubling co2 when the precipitate caco3 is in the co2 test
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
what is the equation for caco3 + co2 when you continue bubbling co2 in the co2 test
CaCO3+H2O+CO2–> Ca(HCO3)2
what is the equation when you test for co2
Ca(OH)2+ CO2 –> CaCO3 + H2O
what is the test for chlorine gas
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
what is the test for ammonia gas
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
what is the test for water
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
what is the equation when you test for water
CuSO4 + 5H2O –> CuSO4.5H2O
Test for Pure Water
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
write the methods for the test for cations
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
when burned, what is the color of lithium
Lithium - crimson red
when burned, what is the color of sodium
Sodium - yellow (sometimes looks like orange
when burned, what is the color of potassium
Potassium - lilac flame
when burned, what is the color of calcium
Calcium - orange-red
when burned, what is the color of copper
Copper (II) - blue-green
what must you keep in mind when testing for lithium
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
which elements are the only soluble ones when testing for cations using sodium hydroxide
Testing for Cations using Sodium Hydroxide
Ammonium, potassium and sodium hydroxide are the only soluble ones (APS).
how do you test for cations using sodium hydroxide
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)
what happens when you add NaOH to a solutuon containing other metla ions
When you add sodium hydroxide to a solution containing other metal ions, a precipitate is formed with that metal (metal hydroxide)
what is the test for iron (iii)
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
write the full and ionic equation when testing for iron (III) ions
FeCl3(aq)+3NaOH–> Fe(OH)3(s) + 3NaCl –> full equation
Fe3+ (aq) + 3OH- (aq) –> Fe(OH)3(s) –> ionic equation
what is the test for copper (II)
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)
write the full and ionic equation when testing for copper (II) ions
CuSO4 (aq) + 2NaOH(aq) –> Cu(OH)2(s) + Na2SO4(aq)
Cu2+(aq)+2OH-(aq)–>Cu(OH)2(s)
test for iron (II)
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)
write the full and ionic equation when testing for iron (II) ions
FeSO4(aq) + NaOH(aq)–> Cu(OH)2(s) + Na2SO4(aq)
Fe2+(aq) + 2OH-(aq) –> Fe(OH)2(s)
when you test for iron (II) why does the green precipitate become orange brown
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
what do you have to do for most precipitation reactions
For all of these precipitations reactions, you always mix solutions as you can’t have a solid and then see a precipitate form
how to test for ammonium ions
Testing for ammonium ions:
As with this reaction you aren’t looking for a precipitate, you can use a solid or a solution
In the cold, there will be enough ammonia gas produced for you to be able to smell it (people with asthma should not smell/inhale ammonia gas)
If you warm it, you can test the ammonia gas given off with damp litmus or universal indicator paper - this would turn blue as ammonia is an alkaline gas
NH4Cl(aq)+ NaOH(aq) –> NH3(g) + NaCl(aq) + H2O(l)
NH4+(aq) + OH-(aq) –> NH3 + 2H2O
How to test for carbonates
To test for Carbonates:
Carbonates are quite insoluble so this test will normally be done with a solid
Soluble carbonates (APS) are ammonium carbonate, potassium carbonate and sodium carbonate
React a carbonate with hydrochloric acid and collect the effervescence
Test the gas by bubbling it through limewater - if it turns cloudy/milky/chalky, it confirms that the gas produced is CO2, confirming that the ion was a carbonate
CO3 2-(s) + H+ –> CO2 +H2O
why should you not smell ammonia when the solution is warm
so with cold solution, there is less amonia so the gas is safe
process for testing for sulfates
Testing for sulfates (think of an insoluble sulfate - i.e. BaSO4
Make a solution by dissolving your ‘test sulfate’ in distilled water
Add some dilute HCl - to remove unwanted anions (some of these could react with the barium and produce a white precipitate, giving a false result)
Add barium chloride solution
If the ‘test sulfate’ actually is a sulfate, then you see a white precipitate form
whats the ionic equation for testing for sulfates
SO4 ^2- (aq) + Ba^2+ (aq) –> BaSO4(s)
process for testing for halides
Testing for Cl-, Br-, I-: REACT THEM ALL WITH SILVER (I)
Make a solution of the ‘test halide’
Add enough dilute nitric acid to make it acidic
Add silver nitrate solution
Cl = white precipitate
Br = cream precipitate
I = yellow precipitate
whats the ionic equation for testing for halides
Ionic Equation: H=Halide
H^-1(aq) + Ag^1+ (aq) –> AgH(s)
