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What metal is stored in kerosene. Chemical properties

PURIFICATION OF ALKALI METALS FROM OXIDE FILMS

It is recommended to remove oxide films from the surface of lithium and sodium pieces with a sharp knife under a layer of xylene or mineral oil, previously dried over sodium wire. The operation is conveniently carried out in a porcelain mortar. The cleaned pieces of metal are transferred with tweezers to a beaker or flask with dried xylene. Metal scraps after careful decanting of xylene are immediately destroyed.

When purifying potassium, this technique cannot be considered safe, although it is recommended in some guidelines. When a fresh potassium surface comes into contact with an oxide film, explosions sometimes occur even under a layer of protective liquid.

Much safer, more economical and easier way purification of potassium, which consists in melting the metal under a layer of dried heptane. Small crude pieces (about 20 g) are melted in a wide-mouthed Erlenmeyer flask or in a tall beaker. After the metal is melted, the heating is stopped and the flask is gently rotated to ensure that potassium flows out of the oxide films. If smaller pieces are needed, gently shake the flask or glass rod to break the portion into several globules. Next, the flask is cooled, and when the metal solidifies, the globules are removed with a sharp iron stick or long tweezers and transferred to a tared bottle with heptane for subsequent weighing. The remaining films are subject to immediate destruction.

The described procedure is also suitable for sodium purification. In this case, dried xylene is used instead of heptane.

DISPOSAL OF ALKALI METAL RESIDUES

lithium waste

Lithium scraps and small (no larger than a pea) pieces of lithium can be destroyed by dissolving in a large amount of cold water in a fume hood.

Lithium dispersions cannot be dissolved in water due to their high reactivity. Residues of the dispersion in the hydrocarbon solvent are destroyed by the gradual addition of ethyl alcohol.

sodium waste

Scraps and sodium residues, in amounts not exceeding 5-10 g, are immediately destroyed by pouring them with small portions of ethyl alcohol until completely dissolved. It is allowed to use isopropyl alcohol containing up to 2% water to speed up the reaction.

There is a way to destroy small pieces of sodium in a flask of cold water. A layer of gasoline 3-5 cm thick is poured over the water. Pieces of sodium are lowered one by one into the flask. The next piece is introduced only after the complete dissolution of the previous one. Sodium dissolves at the phase boundary, the protective layer of gasoline prevents the ignition of hydrogen. The method is convenient, but from the point of view of safety it has no advantages over conventional methods.

It is necessary to monitor the completeness of sodium dissolution during the treatment of sludge with ethyl alcohol after the reactions. Thus, excess sodium after the Wurtz reaction cannot always be completely destroyed with alcohol, since sodium pieces are covered with a crust of halides that are insoluble in alcohol. Subsequent washing with water in such cases leads to ignition of the mass.

Sodium dispersions are decomposed by dropwise addition of anhydrous alcohol in the absence of air.

potassium waste

These wastes are destroyed by flooding them with a mixture of equal amounts of petroleum ether and anhydrous isopropyl alcohol.

Even with tert with -butyl alcohol, the reaction may be too violent.

The destruction is carried out in a glass under a layer of xylene, adding dropwise tert- butyl alcohol. The operation is carried out in a fume hood with the doors closed, with fire extinguishing agents at the ready.

At proper organization work in the laboratory, when scraps do not accumulate, but are destroyed in a timely manner, there is no need to destroy large amounts of alkali metals.

13. Safety precautions when working with
concentrated acids and alkalis

When working with concentrated acids and alkalis, the following precautions must be observed:

1. Pour the indicated liquids only through the funnel fume hood.

2. When diluted concentrated sulfuric acid pour the acid in portions into the water and mix vigorously;

3. When diluted with water concentrated acid, in the manufacture of a chromium mixture, when mixing concentrated sulfuric and nitric acids, only thin-walled dishes.

4. Dissolve caustic alkalis follows by slowly adding small pieces to the water; take pieces of alkali with tongs or a spatula.

5. Caustic, aggressive, defiant chemical burns substances, concentrated acids - hydrochloric, nitric, sulfuric, hydrofluoric and chromic anhydride, dry alkalis - sodium, potassium hydroxides and their concentrated solutions, as well as ammonia solutions, getting on the skin, cause burns. A particular danger is the possibility of damage to the eyes. For all work with caustic substances Necessarily apply protective glasses or masks, gloves .

6. Store caustic substances only in thick-walled glass dishes with a capacity of not more than 2 liters in a fume hood.

7. Transfuse acids only when the draft in the fume hood is switched on. Cabinet doors should be closed as much as possible. It is recommended to pour acids using a special siphon.

8. Flasks with concentrated acids, and bromine carry only in a bucket, and when transfusing, the bottle cannot be held by the neck.

9. When working with fuming nitric acid And oleum, except
glasses, wear long rubber apron.

10. Do not use sulfuric acid in vacuum desiccators as a water absorbent.

11. Working with hydrofluoric acid requires special care. Necessarily wear rubber gloves, goggles and carry out all work only under draft.

12. Spilled acids and alkalis should be immediately neutralize and only after that clean up.

13. Forbidden collect solutions of acids and alkalis, sucking them with your mouth into a pipette.

Calcium is easily oxidized in air, so it, like potassium and sodium, is stored under a layer of kerosene.

When calcium is oxidized in air, calcium oxide is formed, or, as it is called, burnt (quicklime) lime CaO:

2Ca + O 2 \u003d 2CaO

Preheated calcium burns in oxygen, but not as brightly as magnesium. Calcium reacts vigorously with hot water, displacing hydrogen from it and forming calcium hydroxide, or slaked lime Ca (OH) 2:

Ca + 2H 2 O \u003d Ca (OH) 2 + H 2

Under normal conditions, calcium reacts with halogens, and with sulfur, nitrogen and carbon when heated:

Ca + Cl 2 \u003d CaCl 2 Ca + S \u003d CaS 3Ca + N 2 \u003d Ca 3 N 2 Ca + 2C \u003d CaC 2

Calcium, like magnesium, exhibits pronounced reducing properties.

Calcium oxide CaO, like burnt magnesia, has a very high melting point - about 3000 ° C.

In industry, calcium oxide is obtained by firing limestone, chalk or other carbonate rocks:

CaCO 3 \u003d CaO + CO 2

If CaO is poured over with water, then a very violent reaction occurs, accompanied by hissing, strong heating and an increase in volume. As a result of this process, hydrated lime is formed - Ca (OH) 2:

CaO + H 2 O \u003d Ca (OH) 2

A mixture of slaked lime, sand and water is called mortar or lime mortar. It is used as a plaster, as well as for bonding bricks when laying walls, although in the latter case cement mortar is usually used.

The hardening of the lime mortar occurs as a result of the simultaneous occurrence of two processes:

1) precipitation of calcium hydroxide crystals from a supersaturated solution, which firmly bind sand particles together;

2) the formation of calcium carbonate as a result of the reaction:

Ca (OH) 2 + CO 2 (from air) \u003d CaCO 3 + H 2 O

Hydrated lime is a white solid, soluble in water, but its solubility is low. A solution of slaked lime in water is called lime water. It has alkaline properties. When CO 2 is passed through lime water, the solution becomes cloudy, and upon further passage, the turbidity disappears:

Ca (OH) 2 + CO 2 \u003d CaCO 3 ¯ + H 2 O

Ca 2+ + 2OH - + CO 2 \u003d CaCO 3 ¯ + H 2 O

CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2

CaCO 3 + H 2 O + CO 2 \u003d Ca 2+ + 2HCO - 3

Lime water is used as a reagent for carbon monoxide (IV), as well as to eliminate the temporary hardness of water caused by calcium bicarbonate Ca(HCO 3) 2 .

Volatile calcium compounds color the burner flame brick red.

Hardness of water

As you know, pure water practically does not occur in nature - it always contains ions of various salts. Water, which contains a lot of Ca 2+, Mg 2+, Sr 2+, Fe + ions, is called hard, and water hardness is mainly due to Ca 2+ and Mg 2+ ions. In hard water, soap is poorly lathered, vegetables are poorly boiled, and when such water is used in steam boilers, scale is formed, which can lead to a boiler explosion. Hard water must be softened before drinking. Distinguish between carbonate and non-carbonate water hardness.

Carbonate is the hardness of water due to the calcium and magnesium bicarbonates contained in it. When boiling, these salts are destroyed with the formation of hardly soluble carbonates, and Ca 2+ and Mg 2+ ions are removed from the solution:

Ca (HCO 3) 2 \u003d CaCO 3 ¯ + H 2 O + CO 2

PURIFICATION OF ALKALI METALS FROM OXIDE FILMS

A much safer, more economical and easier way to purify potassium is to melt the metal under a layer of dried heptane. Small crude pieces (about 20 g) are melted in a wide-mouthed Erlenmeyer flask or in a tall beaker. After the metal is melted, the heating is stopped and the flask is gently rotated to ensure that potassium flows out of the oxide films. If smaller pieces are needed, gently shake the flask or glass rod to break the portion into several globules. Next, the flask is cooled, and when the metal solidifies, the globules are removed with a sharp iron stick or long tweezers and transferred to a tared bottle with heptane for subsequent weighing. The remaining films are subject to immediate destruction.

The described procedure is also suitable for sodium purification. In this case, dried xylene is used instead of heptane.

DISPOSAL OF ALKALI METAL RESIDUES

lithium waste

Lithium scraps and small (no larger than a pea) pieces of lithium can be destroyed by dissolving in a large amount of cold water in a fume hood.

Lithium dispersions cannot be dissolved in water due to their high reactivity. Residues of the dispersion in the hydrocarbon solvent are destroyed by the gradual addition of ethyl alcohol.

sodium waste

Sodium dispersions are decomposed by dropwise addition of anhydrous alcohol in the absence of air.

potassium waste

These wastes are destroyed by flooding them with a mixture of equal amounts of petroleum ether and anhydrous isopropyl alcohol.

Even with tert with -butyl alcohol, the reaction may be too violent.

With the correct organization of work in the laboratory, when scraps are not accumulated, but are destroyed in a timely manner, there is no need to destroy large amounts of alkali metals.