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Laboratory preparation of oxides

Preparation of red lead

First, prepare a lead carbonate (51 g) precipitation of a solution of 100 g of lead nitrate solution of 51 g of sodium bicarbonate. The precipitate collected, washed with water and dry in air at 40 ° C.

A mixture of 51 g of lead carbonate and 5.4 g of sodium nitrate heated in a porcelain crucible with a small flame, stirring constantly (can also be performed on iron pan). When heated to about 200 ° C, the mixture turns yellow (formation of lead oxide), and releases carbon dioxide. Only when the reaction mixture is a yellow raise the temperature to 450 ° C, and stir continuously. If the mixture starts to blush, add a little at 30-35 g of potassium chlorate and heated with stirring for about 30 minutes. The temperature must not be too high, the decomposition of red lead to lead oxide (Jar not visibly glow during labor)! The reaction mixture was then set aside to cool, spoon and cook with water. Suspension is filtered, decanted several times with hot water and washed until the filtrate shows the reaction to nitrite (oxidation of iodide to iodine). Finally grounds cook with 5% sodium hydroxide solution, filter, rinse with water and dried in air at 100 ° C.

Pb (NO 3) 2 + 2NaHCO 3 -> PbCO 3 + 2NaNO 3 + 2CO 2
3PbCO 3 + NaNO 3 -> Pb 3 O 4 + 3CO 2 + NaNO 2

Preparation of the lead(IV) oxide

Oxidation with chlorine

In a 250 ml beaker, dissolve 40 g of lead nitrate in precisely the required quantity of water (saturated solution) and add 3-4 drops of conc. nitric acid. The solution was filtered into 500 ml beaker male paper filter and add 10% NaOH solution to weakly alkaline to litmus. In the resulting alkaline suspension of lead hydroxide introduce a stream of chlorine, as originally white sediment Brown and has changed color. The mixture boil and filter on a Buchner funnel. Precipitate is washed with distilled water until no reaction for chlorides (try silver nitrate). Precipitate suspended in 10% nitric acid, boil, rinse with distilled water, filter and dry at 110 ° C.

Oxidation of chloride of lime

In a 250 ml beaker, dissolve 40 g of lead nitrate in precisely the required quantity of water (saturated solution) and add 3-4 drops of conc. nitric acid. The solution was filtered into 500 ml beaker male paper filter and add 10% NaOH solution to weakly alkaline to litmus. Fresh bleach at approximately twice the theoretical amount we cover the parts with distilled water in a porcelain mortar to a homogeneous slurry. Dilute slurry equal volume of distilled water, mix and filter after ceasing large folding filter. The filtered solution pouring, stirring the hot alkaline suspension of lead hydroxide, as originally white sediment browns and does not have a color. The mixture boil and filter on a Buchner funnel. Precipitate is washed with distilled water until no reaction for chlorides (try silver nitrate). Precipitate suspended in 10% nitric acid, boil, rinse with distilled water, filter and dry at 110 ° C.

Preparation of chromium trioxide

Prepare a saturated solution of potassium dichromate solution of 100 g of dichromate ax ml water. To this solution add x mL of concentrated sulfuric acid (6 to 8 times the theoretical amount). Cooled down and let stand, excluding the crystals of chromium trioxide, which sucked the ceramic frit and washed with a small amount of concentrated nitric acid. Crystals of dried air is preferably in a desiccator.

Preparation of chromium oxide

Chromium oxide can be prepared by thermal decomposition of ammonium dichromate or chromate ( volcano ).

(NH 4) 2 Cr 2 O 7 -> Cr 2 O 3 + 4H 2 O + N 2
2 (NH 4) 2 Cr 2 O 4 -> Cr 2 O 3 + 4H 2 O + N 2 + 2NH 3

The prepared chromium oxide is chemically resistant and difficult to convert into a solution of mineral acids.

Preparation of copper oxide

To a solution of 10 g of copper sulphate pentahydrate (bluestone) in 100 ml of water in 250 ml beaker pouring 10% sodium hydroxide solution (about 35 ml) in making gelled precipitate of copper hydroxide (slight excess of sodium hydroxide does not matter). Mixture in a beaker and heated to boiling temperature is kept around 20 minutes. Originally blue precipitate of copper hydroxide Brown (created copper oxide).

Resulting black precipitate of copper oxide few carefully decanted to remove the adsorbed sodium sulphate or other salt if we used as a source of copper sulfate other than salt. Precipitate filtered off and dried in air.

Preparation oxide

To a solution of 1% sodium hydroxide solution, pouring a solution of mercuric chloride (we can also use other soluble mercuric salt) until they form a yellow precipitate oxide (přiléváním hydroxide to a solution of mercuric chloride to form a precipitate of dark colored oxychloride mercury). Clot Decant water, filter and dry in air.

The prepared mercuric oxide used for further preparation as a starting material, because we can determine exactly how many contain mercury, which is the chloride or nitrate difficult (they are strongly hygroscopic).

Preparation of calcium oxide

Calcium oxide prepare precipitation of calcium salts with an alkaline carbonate (calcium carbonate) and its subsequent thermal decomposition at ca x C.

The precipitated carbonate is necessary to carefully decant that we got rid of soluble salts to precipitate carbonate naadsorbovaných.

The prepared calcium oxide is very clean and can be used for example in an attempt ILLUMINATED COLOUR where high purity and the exact amount chemicals necessary for success.

In the case of small claims to purity can use quicklime (calcium oxide with additives)

Preparation of tin oxide

The concentrated solution of stannous chloride okyselíme conc. hydrochloric acid to prevent hydrolysis are: if the solution is cloudy and it filtered. Then add concentrated sodium carbonate solution until alkaline. A solution of the resulting precipitate partially evaporated a porcelain bowl, a clot decanted hot water, will transfer to the filter and washed with water to remove chlorides (try silver nitrate). The resulting precipitate, which has a gray color, dry it at 130 to 150 ° C with exclusion of air.

SnCl 2 + Na 2 CO 3 -> SnCl3 + 2NaCl
SNCO 3 -> SnO + CO 2 thermal decomposition

Preparation of the bismuth(III) oxide

1.5 g of alkaline nitrate bizmutitého pour into a porcelain crucible and heat the gas burner. Warmed gently at first and then annealed, the crucible leaking brown fumes of carbon dioxide and rise gradually melt carbon bizmutitého. After twenty minutes, interrupted annealing pot and let the product cool down. Yield about 0.89 g (75% of theory).

2 [4BiNO 3 (OH) 2BiO (OH)] -> 5Bi 2 O 3 + 8 NO 2 + 9H 2 O + 2O 2

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