Compounds Of The S-Block Elements Essay, Research Paper
`We are provided with 3 salts X, Y
and Z which contain a different s-block element. We are to carry out the
reactions listed below and report the observations and deductions in the table.1.
Heat about 0.5g of solid X in a clean dry test tube and test
the gas evolved with a glowing splint.?
Continue heating until there is no further change and allow the residue
to cool. Observation Inference Lighted splint goes out when placed into test tube. Cannot be oxygen as the lighted splint would ignite and
cannot be hydrogen, as the lighted splint would cause a popping sound. Could
be carbon dioxide or another gas that causes the splint to goes out. 2.
Use a fume cupboard for this test.? Add 2 cm3 dilute hydrochloric acid to the cooled
residue. Identify the gas evolved. Observation Inference Residue releases a brown gas The brown gas shows that nitrogen dioxide is present and
so NO3- ion must be present with the metal NO3-
ion. The first 2 experiments show that X is a nitrate and the
metal in X cannot be in group 2 as on heating a group 2 metal nitrate, would
cause the compound to decompose to metal oxide, brown nitrogen dioxide and
oxygen, this clearly did not happen until experiment 2 when HCl was added.? The HCl reacted with the residue (Metal
Nitrite) to give off metal chloride, nitrogen dioxide and water.3.
Make a solution of X in 5 cm3-distilled water. Take
half of this solution and add 1 cm3 of silver nitrate solution followed
by an equal volume of dilute nitric acid. Observation Inference Clear No halide ions present. Experiment 3 is done in a
different way then the usual method.?
The nitric acid is to remove any other compounds, which would
interfere.? The test solution is made
acidic with dilute nitric acid to ensure the removal of carbonates or sulphates
ions, which would interfere by giving a spurious precipitate, and then add the
silver nitrate solution.? A precipitate
then forms.4.
Heat solid about 0.5g of Y in a clean dry test tube and
identify the gases evolved.? Continue
heating until there is no further change and allow the residue to cool. Observation Inference Bubbles released and condensation appears to be present. Hydrogen is released but afterwards the limewater goes
milky hence showing CO2 is present.? The condensation shows that water is present. 5.
Add 1 cm3 of dilute hydrochloric acid to the cooled
residue. Observation Inference Effervescence.??
Bubbles released (gas) Water is present.Metal Oxide +
Hydrochloric Acid → Water + Metal Chloride Test 4 and 5 shows that
elements oxygen, carbon, hydrogen and the metal are present.? The compound cannot be a carbonate because
hydrogen is present. Therefore Y could contain HCO3-
ions. 6.
Make a solution of about 0.5g of solid Y in 5 cm3
of distilled water and then take half of this and add 1 cm3 of
silver nitrate solution followed by an equal volume of dilute nitric acid. Observation Inference After Siler Nitrate ? Milky creamy After Nitric Acid ? Precipitate dissolves. No Halide ions present. Usually in this experiment if the solution becomes cloudy
after the silver nitrate it means there is a halide present. But like
experiment 3, this experiment is done differently.? Since you did not remove the carbonates, before adding the silver
nitrate, the carbonates interfere by giving a spurious precipitate.? By adding the nitric acid you remove the
carbonates and the precipitate dissolves.?
If you first add the nitric acid to solution Y then add the silver
nitrate, the precipitate would be clear showing that there is no halide ions.7.
Make a solution of about 0.5g of solid Z in 5 cm3
of distilled water and then take half of this and add 1 cm3 of
silver nitrate solution followed by an equal volume of dilute nitric acid. Observation Inference After Siler Nitrate ? Milky creamy After Nitric Acid ? White precipitate Halide ion present. Br – ion present. Again like test 3 and 6 this
experiment is done differently and has to be interpreted differently.? The nitric acid removes any impurities so
since this was added after the silver nitrate the halide ion present is Cl-.? We can say if you add the nitric acid then
the silver nitrate the precipitate would be white, and the white precipitate
shows that chlorine ions are present.8.
Carry out the flame test to identify the cations in X, Y and
Z. Observation Inference X ? Lilac Y ? Orange / Yellow Z ? Brick Red K+ Na+ Ca+ The heat energy of the flame
causes electrons to be excited within the metal atoms hence raising them to a
higher energy level. When these electrons return to the lower energy levels
they emit characteristic colours.? Group 1 ? Lithium??????????????? Carmine red Flame colours of the S-block elements. ??????????????? ?? Sodium??????????????? Yellow ??????????????? ?? Potassium?????????? LilacGroup 2 ? Calcium??????????????? Brick Red ??????????????? ?? Strontium??????????? Crimson
Red ??????????????? ?? Barium ??????????????? Apple
GreenFormulae of:X = KNO3???????????????????????????????????????????? Y
= NaHCO3???????????????????????????????????????? Z
= CaCl2 Potassium Nitrate???????????????????????????????? Sodium Hydro
Carbonate?????????????????? Calcium
ChlorideChemistry