Continuation. See No. 34, 35, 36, 37, 38/2003
HNO 3 is a strong oxidizing agent.
Concentrated nitric acid oxidizes nonmetals to higher oxidation states:
Passivation occurs due to the formation of insoluble films of metal oxides:
2Al + 6HNO 3 = Al 2 O 3 + 6NO 2 + 3H 2 O.
HNO 3 (conc.) can be stored and transported without access to air in containers made of Fe, Al, Ni.
A qualitative reaction is the interaction of HNO 3 with Cu to form a brown NO 2 gas with a pungent odor (in addition, salt and water are formed).
As the concentration (dilution) decreases, HNO 3 with Zn can form various nitrogen-containing products:
and also in all cases salt and water.
Note
. To recognize the nitrate anion, a diphenylamine indicator is used (a solution of (C 6 H 5) 2 NH in conc. H 2 SO 4).
Demonstration experience
. Recognition is carried out “by traces” or by droplet contact: a dark blue color appears. Nitrates– salts of nitric acid, solid crystalline substances.
, highly soluble in water. Nitrates of alkali metals, calcium and ammonium –
saltpeter
| Most nitrates are very good mineral fertilizers. | Nitrates are strong oxidizing agents! Coal, sulfur and other flammable substances burn in molten nitrate, since all nitrates (like HNO 3) release oxygen when heated and, depending on the chemical activity of the metal, salts give different products: | Operating procedure |
|---|---|---|
| Tasks Observations and conclusions Assemble the device (according to the diagram), put a little crystalline sodium (Chilean) nitrate in a cup, melt it.
|
Heat a piece in the flame of an alcohol lamp | |
| Take samples of all three solutions in test tubes No. 1–3 (see No. 38/2003) and first pour approximately an equal amount (volume) of concentrated sulfuric acid into each sample, then add a little copper shavings and heat a little. Observe characteristic changes in one of the samples | Three numbered test tubes contain solutions of sodium chloride, sulfate and sodium nitrate. Recognize the saltpeter solution. Why is concentrated sulfuric acid first added to the nitrate solution? Write molecular and ionic equations for the reaction. Check the output using a trace reaction with a diphenylamine indicator. |
Complex substances (turpentine, wood, sawdust) can also burn in nitric acid.
A mixture of concentrated nitric and sulfuric acids (nitrating mixture) with many organic substances forms nitro compounds (nitration reaction).
| Most nitrates are very good mineral fertilizers. | Nitrates are strong oxidizing agents! Coal, sulfur and other flammable substances burn in molten nitrate, since all nitrates (like HNO 3) release oxygen when heated and, depending on the chemical activity of the metal, salts give different products: | Operating procedure |
|---|---|---|
| A mixture of 1 volume of HNO 3 (conc.) and 3 volumes of HCl (conc.) is called “aqua regia”. Even gold Au and platinum Pt dissolve in such a mixture: In a test tube with concentrated nitric acid | (1 ml) add some copper shavings (Cu). If the effect is delayed, warm it up a little. Work under traction! Pour the products from the sanitary bottle into the sewer system and rinse with a stream of water. | |
| What explains the release of brown gas with a pungent odor? Considering that water and copper(II) nitrate are also formed, write the reaction equation. Draw up an electron balance diagram and write the reaction equation in ionic form | Mix fine-crystalline sulfur (S) powder with 1 ml of concentrated HNO 3, heat the mixture (under draft). Take a sample of the reaction products and test it with 2-3 drops of barium chloride solution. Immediately pour products from the sanitary bottle into the sewer system |
Practical work 14. Determination of orthophosphates
Goals. A rack with test tubes, glass tubes with rubber rings, a sanitary bottle, spatulas (3 pcs.);
| Most nitrates are very good mineral fertilizers. | Nitrates are strong oxidizing agents! Coal, sulfur and other flammable substances burn in molten nitrate, since all nitrates (like HNO 3) release oxygen when heated and, depending on the chemical activity of the metal, salts give different products: | Operating procedure |
|---|---|---|
| crystalline Ca 3 (PO 4) 2, CaHPO 4, Ca(H 2 PO 4) 2, distilled water, universal indicator, solutions of H 3 PO 4, NaCH 3 COO (= 10%), AgNO 3. | Pour 1 cm 3 of calcium orthophosphate, hydrogen orthophosphate and calcium dihydrogen orthophosphate into three test tubes, add a little (the same amount) of water, mix | … |
| Draw a conclusion about the solubility of primary, secondary and tertiary orthophosphates. Can the different solubilities of these phosphates be considered a method for their recognition? | Using aqueous solutions and suspensions in three test tubes from the previous experiment, test them with a universal indicator | … |
| Determine the pH of all solutions on a scale and explain why the pH in this case has different values K aqueous solution phosphoric acid in one test tube (1 ml) and superphosphate solution in another (1 ml) add 10% sodium acetate solution and |
a few drops of silver(I) nitrateWhat is the reagent for an ion? | … |
Practical work 14."Nitrogen subgroup"
Goals. Review the composition and properties of nitrogen and phosphorus compounds, their interconversions and methods of recognition.
. Alcohol lamp, matches, blue glass, filter paper, test tube holder, rack with test tubes (2 pcs.), spatulas (3 pcs.), mortar, pestle, sanitary bottle;
in test tubes No. 1–3:
Option I
– double superphosphate, NH 4 NO 3, (NH 4) 2 SO 4,
Option II
– NH 4 Сl, NaNO 3, KCl,
Option III
– KNO 3, (NH 4) 2 SO 4, double superphosphate;
crystalline salts (NH 4) 2 SO 4, NH4Сl, ammophos, aqueous solutions of CH 3 COONa (= 10%), AgNO 3, BaCl 2,
CH 3 COOH ( = 10%), NaOH, litmus paper, CuO, Cu (chips), HNO 3 (dil.), HNO 3 (conc.), H 2 SO 4 (conc.), diphenyl indicator, (C 6 H 5) 2 NH in concentrated H 2 SO 4,
Ca(OH) 2 (dry), distilled water, AgNO 3 in HNO 3, in test tubes No. 4–6 dry crystalline substances: Na 2 SO 4, NH 4 Cl, NaNO 3, in test tubes No. 7 and 8: H 3 PO 4 and H 2 SO 4 (diluted solutions), in test tubes No. 9 and 10: Na 3 PO 4 and Ca 3 (PO 4) 2. Experimental task
Table
| Substance name | Appearance | Solubility (in water) | The interaction of a solution of this salt with | Flame coloring | |||
|---|---|---|---|---|---|---|---|
| H 2 SO 4 (conc.) and Cu |
solutions of BaCl 2 and CH 3 COOH | NaOH solution when heated | AgNO 3 solution | ||||
| Ammonium nitrate NH 4 NO 3 | good | NO 2, brown, with a pungent odor | – | NH 3, colorless, with a pungent odor | – | Yellow (from impurities) |
|
| Ammonium chloride NH 4 Cl | White crystalline powder | good | – | – | NH 3 | AgCl, white precipitate | Yellow (from impurities) |
| Potassium nitrate KNO 3 | Light gray small crystals | good | NO 2 | – | – | – | Purple |
| Ammonium sulfate (NH 4) 2 SO 4 | Colorless large crystals | good | – | BaSO 4, white, insoluble in CH 3 COOH | NH 3 | Ag 2 SO 4, white, highly soluble in acids | – |
| Superphosphate Ca(H 2 PO 4) 2 2H 2 O | Light gray powder or granules | Dissolves slowly | – | Ba 3 (PO 4) 2, white, partially soluble in CH 3 COOH |
– | Ag 3 PO 4, yellow (in the presence of CH 3 COONa) | Brick- red |
| Silvinite KCl NaCl | Pink crystals | good | – | – | AgCl | Yellow with hints of purple | |
| Potassium chloride KCl | Colorless crystals | good | – | – | – | AgCl | Purple |
Solution
All ions in an aqueous environment colorless, it is impossible to recognize them by color.
2) Since none of the substances (flasks No. 1–4) are characterized by worse solubility, the solutions cannot be distinguished by this criterion; all are transparent solutions.
3) Two solutions contain the same cations, but all contain different anions, so qualitative recognition should be based on the anions. Reagent for – AgNO 3 in the presence of a 10% solution of CH 3 COONa (or BaCl 2 and CH 3 COOH);
reagent – BaCl 2 solution; reagent for Cl – solution of AgNO 3 in HNO 3 ; reagent - concentrated H 2 SO 4 and Cu (chips). You can immediately identify, then, using one reagent (AgNO 3), recognize all three remaining solutions (or vice versa). Other options take longer and require significantly more reagents. 4) Test all four solution samples with AgNO 3 solution (1–2 drops): the solution from bottle No. 4 remained unchanged - it should be a NaNO 3 solution; in flask No. 2 there is a white crystalline precipitate, insoluble in acids, this is a KCl solution; the other two samples give cloudy solutions, when added to which a 10% solution of CH 3 COONa, sample No. 3 gives a precipitate yellow color
is a solution of Na 3 PO 4, and sample No. 1 is a solution of (NH 4) 2 SO 4 (the turbidity disappears when the acid HNO 3 is added).
Add 1-2 drops of BaCl 2 and CH 3 COOH solutions to the sample solution from bottle No. 1, the solution becomes milky in color, because a white crystalline precipitate precipitates:
You can check the same sample by adding an alkali solution with heating. NH 3 gas is released, determined by the characteristic odor and blueness of wet red litmus paper. Reaction equation:
Add concentrated H 2 SO 4 and Cu (shavings) to the solution sample from bottle No. 4 and heat slightly. A brown gas with a pungent odor is released, and the solution becomes a greenish-azure color:
5) Conclusion .
In bottles:
No. 1 – solution (NH 4) 2 SO 4,
No. 2 – KCl solution,
No. 3 – Na 3 PO 4 solution,
No. 4 – NaNO 3 solution.
Determined solutions |
|||
| № 1 | № 2 | № 3 | № 4 |
| (NH 4) 2 SO 4 | KCl | Na3PO4 | NaNO3 |
| All solutions are transparent and colorless | |||
| +AgNO3 | |||
| Cloudiness of the solution (Ag 2 SO 4, soluble in acids) |
White cheesy sediment (AgСl | According to the option, write down which salt solutions are given in test tubes No. 1–3. Determine where each of these substances is located. In the conclusions, write down the equations of the reactions carried out in molecular and ionic forms. Note the signs of each qualitative reaction | … |
| 1) In a test tube with a small amount CuO (at the tip of a spatula), add HNO 3 solution, shake. 2) Place some copper shavings into a test tube with concentrated HNO 3 (if the effect is not immediately observed, warm the mixture a little) |
Using the given reagents, prepare a solution of copper(II) nitrate in two ways. Note the signs of reactions and write molecular and ionic equations reactions. Which reaction is redox? |
… | |
| In a mortar, mix and grind the mixture of Ca(OH) 2 (slightly moistened) with ammonium salt, sniff carefully. Repeat the experiment with other ammonium salts |
To prove experimentally that sulfate, Ammonium nitrate and chloride should not be mixed with lime. Give appropriate explanations |
… | |
| Draw up a recognition plan (order) that is most efficient in terms of time and reagent consumption | In test tubes No. 4–6, determine crystalline sodium sulfate, ammonium chloride and sodium nitrate. Write the reaction equations. Note observed signs of reactions |
... | |
| It is best to test solution samples in test tubes No. 7 and 8 with BaCl 2 and CH 3 COOH reagents, watching the result very carefully while shaking the reaction mixture |
By qualitative recognition, determine Which of the test tubes No. 7 and 8 contains the solutions? sulfuric and orthophosphoric acids. Write reaction equations |
... | |
| Make a plan for recognizing the substances Na 3 PO 4 and Ca 3 (PO 4) 2 in test tubes No. 9 and 10 |
Determine practically in test tubes No. 9 and 10 crystalline sodium and calcium orthophosphates |
... | |
