Ion Analysis Flashcards
What is the method for the flame test?
- Clean wire/needle with concentrated HCl
- Dip wire into HCl (to wet needle) and place in compound
- Place compound in blue bunsen flame
What do ionic compouds consist of?
Cations (positively charged) and anions (negativley charged)
How can ionic compouds be identified?
using different tests (4 tests to identify the cation and 5 to identify the anion).
What are the tests to identify the cation in an ionic compound?
- Flame test
- NaOH test
- NH3 test
- NH4^+ test
What are the tests to identify the anion in an ionic compound?
- Halide test
- SO4^2- test
- SO3^2- (sulfite) test
- CO3 test
- NO3 test
What happens to an ion when you heat it in the flame test (in steps)?
- It is first in it’s ground state (meaninfg that the electrons are arrangesd as we know them to be).
- when heat is applied, the ion reaches an excited state. the electron absorbs energy and moves further away from the nucleus, the electron is promoted (it usually moves only one energy level upward and it is usualy only one electron.
- Once the heat is removed the electron returns to the ground state and as that happes, energy is released.
What happens to an ion from the ground state to the excited state?
The electron is promoted. The electron absorbs energy and moves further away from the nucleus (usually only one energy level and always only one electron).
What happens to an ion when it returns from the excited state to the ground state?
As the electron returns to the ground state energy is released as light. This light is a specific color depending on the cation in the compound.
What does the color of the light in the flame test depend on?
The wavelength of the light emitted. each ion absorbs/emits a different quantity of energy. Less energy is emmitted if the ion has lower electrostatic forces (ionic radius, ionic charge)
What color is emitted in the flame test when the most possible energy is released?
Purple or (U.V. light)
What color is emitted in the flame test when the least possible energy is released.
Red or (I.R. light)
Complete the table
Which tests use precipitation in this unit?
- NaOH (cation)
- NH3 (cation)
- Sulfate (anion)
- Halides (anion)
Complete the table
What ions could you use for the sulfate experiment and why?
Could use: Ca^2+ / Sr^2+ / Ba^2+ / Pb^2+
We could use these ions because if the compound the react with does indeed have a sulfate than it will be insoluble.
What ion is best used in the sulfate test and why?
Ba^2+, because it is the most insoluble.
What is the method for the sulfate experiment?
- Dissolve sample in water
- Add any acid (to remove OH^- / CO3^2- ) except H2SO4
- Add Ba compound e.g. Ba(NO3)2
- If sulfate is present
=> white ppt is formed
What is the method for the sulfite test?
Add in some of the equations used
-
Reaction 1
1. Add any acid to solid solution
XSO3 (aq) + 2HCl (aq) => XCl2 (aq) (salt) + H2O (l) + SO2 (g) (sulfurdioxide)
2. Collect gas produced (if no gas, is not SO3) -
Reaction 2
1. Expose the gas to either K2CrO7 (potassium dichromate) or KMnO4 (potassium mangnate.
With K2Cr2O7: Cr^6+ (orange) =SO2=> Cr^3+ (green)
With KmnO4: Mn^7+ (purple) =SO2=> Mn^2+ (pink/colorless)
What is the method of the carbonate test?
Add some of the equations used
-
Reaction 1
1. Add any acid
XCO3 + 2HCl => XCl2 + H2O +CO2
2. Collect gas produced -
Reaction 2
3. Add gas to limewater
CO2 (g) + Ca(OH)2 (lime water (very low conc.) would not excpect to be soluble) => CaCO3 (s) + H2O
4. If CO2 was produced white ppt is formed (colorless => cloudy)
Write the following chemicals into symbols, their charge, and if they are a cation or anion.
* Sulfate
* Sulfite
* Carbonate
* Ammonium
* Ammonia
* Nitrate
- Sulfate = SO4^2- (anion)
- Sulfite = SO3^2- (anion)
- Carbonate = CO3^2- (anion)
- Ammonium = NH4^+ (cation)
- Ammonia = NH3 (gas)
What is interesting about ammonia?
MOST gases are acids or neutral but ammonia (NH3) is a base
What is the method for the test of ammonium?
-
Step 1
1. React compound with NaOH
2. Heat
NH4X (aq) + NaOH (aq) => NaX (aq) (salt) + H2O (l) + NH3 (g) NOTE: it is a proton transfer -
Step 2
3. Collect gas and expose to damp red litmus
4. If ammoia is present => blue
What is the method for the nitrate test?
-
Step 1
1. Add compound to NaOH
2. React Al powder
3. Heat
NO3 =NaOH =Al=> NH3 -
Step 2
1. Collect gas and expose to damp red litmus
2. If nitrate is present => blue
What is the method for the halides test (Cl-, Br-, I-) e.g. chloride?
- Dissolve
- Add any acid (not HCl) to remove OH^- /CO3^-
- Do sulfate test first!!!
- Add AgNO3 and observe color of ppt.
Complete the table
What are the solubility rules? (differentiate the most important rules to the ordinary ones).
- All compounds of group 1 are soluble
- All nitrates are soluble
- All halides are soluble except if they also contain Ag+ or Pb^2+
- All sulfates are soluble except if they also contain Ca+, Sr^2+, Ba^2+, Pb^2+
- All hydroxides are insoluble
- All oxides are insoluble , but group 1 metals react with water.
What ions could you use for the halide test, which one is typically use and why?
Could use: Ag^+ or Pb^2+. We usually use Ag^+ because it makes a bigger range of colors.
