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 the

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