LABORATORY WORK 2. "DETERMINATION OF THE MASS FRACTION OF IRON IN SOLUBLE SALTS OF IRON(II) OR IRON(III)"

Purpose of the work

Learn to use the precipitation method to determine the mass fraction of a component in a sample by obtaining an amorphous sediment as the precipitated form and calcining the latter to a constant mass.

Targets

1. Bringing the crucible to constant mass.

2. Calculation of the optimal mass of a sample sample. Calculation of the optimal volume of precipitant - ammonia solution.

3. Taking a sample sample.

4. Dissolution of the sample. Oxidation of iron(II) to iron(III) with nitric acid.

5. Obtaining a precipitated form in the form of an amorphous precipitate of iron(III) hydroxide.

6. Separation of iron(III) hydroxide precipitate from the mother liquor by filtration.

7. Washing the iron(III) hydroxide precipitate.

8. Obtaining a gravimetric form of iron(III) oxide by calcining the iron(III) hydroxide precipitate to constant weight.

9. Calculation of the mass fraction of iron in the sample.

10. Statistical processing of the results of parallel determinations of the mass fraction of iron in the sample.

Self-study assignment

For the lesson you need to know: see paragraph above. 1-4, 6 b, 7. For the lesson you must be able to: see paragraphs above. 1, 2 b, 3, 5. Questions for self-test: see paragraphs above. 1-4, 5 b, 6 b, 7-11, 14, 15, 16 b, 17, 19, 20, 21 b, 23-34.

Material support

Dishes(per 1 student)

The rest - see laboratory work 1 above. Reagents(qualifications “analytical grade” or “chemical grade”)

1. Soluble iron(III) or iron(II) salts: ferric ammonium alum, Mohr’s salt, etc.

2. Concentrated nitric acid.

3. Ammonia 10% aqueous solution.

4. Ammonium nitrate 1% solution.

5. Barium chloride 0.2 mol/l solution. Devices: see lab 1 above.

Other required equipment: ashless filters “red ribbon”.

The rest - see laboratory work 1 above (except for point 6). Educational tables.

Method for determining the mass fraction of iron in soluble iron(II) or iron(III) salts

1. The essence of the technique

Determination of iron in soluble salts of iron(II) or iron(III) is based on the preliminary oxidation of iron(II) to iron(III), precipitation of iron(III) hydroxide (precipitable form), calcination and weighing of iron(III) oxide (gravimetric form ).

Iron(III) is precipitated as a practically insoluble amorphous precipitate of iron(III) hydroxide by the action of ammonia:

Instead of ammonia, caustic alkalis should not be used for precipitation, since the iron(III) hydroxide precipitate adsorbs a noticeable amount of alkalis, which are difficult to remove when washing the precipitate.

When precipitating with an ammonia solution, it is necessary that the iron in the solution be in oxidized form. The iron(II) ion is not quantitatively precipitated by ammonia, since, along with the formation of sparingly soluble

hydroxide, soluble iron(II) complexes are also formed. In this regard, after dissolving a sample of the analyzed sample in water, iron(II) is oxidized to iron(III) by the action of a concentrated solution of nitric acid (or a solution of hydrogen peroxide) when heated:

Both iron(II) and iron(III) salts are subject to treatment with nitric acid, since in the latter, as a result of the ingress of organic dust from the air, partial reduction of iron(II) to iron(III) can occur.

It should be noted that nitric acid serves not only to oxidize iron(II), but also to prevent the hydrolysis of iron salts, which occurs with the formation of sparingly soluble basic salts of this element:

If iron(II) is not completely oxidized to iron(III), under the action of ammonia, instead of a red-brown precipitate of iron(III) hydroxide, a black precipitate of iron(II) and iron(III) hydroxide of uncertain composition is formed, which is very stable upon calcination. That is why, if a black precipitate is obtained, it is dissolved in a dilute solution of nitric acid when heated and precipitation with ammonia is repeated.

The precipitated form - iron(III) hydroxide - by its nature forms voluminous amorphous sediments, which are characterized by pronounced adsorption ability. The amount of adsorbed impurities depends on the size of the sediment surface; therefore, the precipitation of iron(III) hydroxide is carried out under conditions that ensure the production of a well-coagulated compact sediment with the smallest surface area. Precipitation is carried out when the solution is highly supersaturated relative to the precipitated form under the following conditions:

a) precipitation is carried out from a concentrated solution with a concentrated solution of a precipitant;

b) the precipitant solution is added quickly;

c) to prevent the formation of colloidal particles, precipitation is carried out from a hot solution, preferably in the presence of a coagulant electrolyte.

After precipitation, the solution with the amorphous precipitate is immediately diluted with hot water (to reduce contamination of the precipitate by adsorbed impurities) and immediately filtered.

When filtering amorphous sediment, a loose, ashless “red ribbon” filter is used. The precipitate can be washed with hot water (in this case, the loss of substance due to the very low solubility of the precipitate is negligible, and the use of hot water prevents peptization of the precipitate). However, to more effectively prevent peptization, it is recommended to wash the sediment with a hot diluted solution of a coagulant electrolyte. As the latter, ammonium nitrate should be used, but not ammonium chloride, since the use of ammonium chloride can lead to loss of the substance as a result of volatilization of iron(III) chloride during subsequent calcination of the precipitate.

Gravimetric form- iron(III) oxide is obtained by calcining the precipitated form at a temperature of 800-900 °C:

Calcination at higher temperatures should not be carried out to avoid partial thermal decomposition of iron(III) oxide:

Gases formed during ashing of the filter, as well as products of incomplete combustion of gas in the burner, can reduce iron(III) oxide to iron(II) and iron(III) oxide, to iron(II) oxide and even to metallic iron. In order to avoid this, it is necessary to ensure sufficient air access to the precipitate during calcination.

The mass fraction (in percent) of iron in the sample is calculated from the masses of the gravimetric form and the sample taken.

The main sources of errors in the determination of iron are due to the content of silicic acid in the ammonia solution, which coprecipitates with iron(III) hydroxide. This is why you should not use an ammonia solution that has been stored in a glass container for a long time. If iron(III) hydroxide precipitates from a solution containing chlorides, the insufficiently washed precipitate may contain a significant amount of coprecipitated iron(III) chloride, which volatilizes when the precipitate is ignited. The admixture of silicic acid gives overestimated results, and the admixture of iron(III) chloride and the conversion of iron(III) oxide into iron(II) and iron(III) oxide gives an underestimated iron content.

2. Preliminary calculations2.1. Calculation of sample weight

The optimal mass of the sample is calculated in accordance with the recommendations given earlier. Approximate mass value

The teacher indicates the percentage (in percent) of iron in the sample. The gravimetric factor for determining iron by the mass of iron(III) oxide is found from the “Handbook”. The mass of the sample is calculated approximately to the second significant digit.

2.2. Calculation of the volume of the precipitant solution

A 10% aqueous ammonia solution is used as an iron(III) precipitant.

1. Mass fraction (percentage) of iron % in the sample is calculated by the formula:

Where - mass of iron in a sample, g; m(weight) - weight of the sample

razza, g; , % - approximate mass fraction of iron in the sample, %.

2. To calculate the mass of the precipitant required for the precipitation of iron(III), make up the proportion based on the reaction equation, according to which 3 moles of precipitant are consumed per 1 mole of iron(III):

Where And - molar masses of iron(III) and precipitant according to

respectively, g/mol.

3. To determine the volume of the precipitant solution V you need to know its density p (see “Reference book”). Then, taking into account that the mass fraction % shows the number of grams of precipitant contained in 100 g of solution; it is easy to calculate the volume of ammonia solution containing grams of precipitant:

4. Since ammonia is a volatile precipitant, a two or three times excess of it compared to the calculated stoichiometric amount is recommended.

5. The final formula for calculating the volume of the precipitant solution has the form:

The volume of the precipitant solution is calculated approximately to the second significant digit.

3. Bringing the crucible to constant mass

Calcination of the crucible to constant weight is carried out in a muffle furnace at a temperature of 800-900 °C (see laboratory work 1).

4. Taking a sample sample

A sample sample with a mass close to the calculated one is first weighed on a pharmacy scale (with an accuracy of ±0.05 g), then transferred to a clean and dry bottle and weighed on an analytical balance (with an accuracy of ±0.0002 g). The contents of the bottle are carefully poured into a beaker with a capacity of 300-400 ml, intended for the precipitation of iron(III) in it. The bottle with the remaining sample is weighed again with the same accuracy. The mass of a sample is calculated as the difference between the first and second weighing results on an analytical balance.

5. Dissolution of a sample sample

A clean glass rod with a rubber tip facing outwards is lowered into a glass with a sample sample, the mass of which is precisely known, and the sample is treated with 10-15 ml of distilled water, measured with a measuring cylinder. Water is added, avoiding splashing, over a glass rod, leaning the nose of the cylinder against it.

ATTENTION! The glass rod is not removed from the glass until the determination is completed.

The contents of the glass are stirred with a glass rod and the appropriate amount of concentrated nitric acid solution is added along the wall of the glass: 1.0-1.5 ml if the iron(II) salt is analyzed, and 0.5-1.0 ml if the iron(III) salt is analyzed ). The contents of the glass are mixed again, after which the glass is placed on an asbestos mesh and heated on a gas burner (or on an electric stove with a closed spiral) until the solution is close to boiling (you cannot boil, since the steam can entrain droplets of liquid from the glass).

ATTENTION! Before heating, make sure that the outer surface of the glass is completely dry.

Heating is continued until the sample is completely dissolved and the solution turns yellow due to complete oxidation of iron(II) to iron(III).

Simultaneously with the analyzed solution, a flask with distilled water and a wash with a 1% ammonium nitrate solution are also heated for the purpose of using them in further work.

6. Obtaining a deposited form

A certain volume of 10% ammonia solution is added one stick at a time to the hot test solution of yellow iron(III) salt while stirring. This volume should be equal to the sum of two volumes of ammonia solution:

1) the volume required to neutralize the nitric acid contained in the analyzed solution;

2) the volume required for almost complete precipitation of iron(III) in the form of iron(III) hydroxide.

The first volume should be 2-2.5 times greater than the volume of a concentrated solution of nitric acid previously added to the analyzed solution. The second volume is pre-calculated (see above). If the volume of ammonia solution is determined correctly, after adding it to the analyzed solution, a faint odor of ammonia should be felt.

To reduce the coprecipitation of impurities by an amorphous precipitate of iron(III) hydroxide, 100-150 ml of hot distilled water is added to the solution with the resulting red-brown precipitate immediately after precipitation.

The contents of the glass are stirred, the precipitate is allowed to settle (3-5 minutes), after which the completeness of iron(III) precipitation is checked by carefully adding 2-3 drops of ammonia solution along the wall of the glass. Precipitation is considered complete if the formation of red-brown sediment flakes is not observed. Almost complete precipitation is also indicated by the fact that the initially yellow solution becomes colorless at the end of precipitation. After precipitation, immediately begin filtering and washing the amorphous precipitate.

7. Separation of precipitate from solution by filtration

To separate the amorphous sediment, an ashless paper filter “red ribbon” is used. Transfer of the precipitate to the filter and filtration are carried out as described above in laboratory work 1.

8. Washing the sediment

A hot 1% solution of ammonium nitrate is used as a washing liquid. Techniques and methods for washing sediment - see laboratory work 1.

The last portions of the washing liquid flowing from the funnel are checked for completeness of washing the sediment from the impurity of sulfate ion or chloride ion, depending on which iron salt is analyzed. To check the completeness of washing from the sulfate ion, about 1 ml of the filtrate is collected in a semi-micro tube and a few drops of a 0.2 mol/l barium chloride solution are added to it. The absence of turbidity (white precipitate) upon addition of the reagent indicates almost complete removal of the sulfate ion. Otherwise, washing the filter cake is repeated until the reaction to sulfate ion is negative. The reagent for the chloride ion is a 0.1 mol/l solution of silver nitrate.

9. Obtaining a gravimetric form

Drying the sediment, ashing the filter - see laboratory work 1. Calcination of the sediment to constant weight is carried out in a muffle furnace at a temperature of 800-900 °C.

10. Calculation of the analysis result

The mass fraction (in percent) of iron in the sample is calculated using the formula:

Where - mass of gravimetric form - iron(III) oxide, g; m(on-

weight) - mass of sample sample, g; gravimetric factor

11. Statistical processing of results of parallel determinations

For n the results of parallel determinations of the mass fraction (in percent) of iron in the sample, %, calculate the average, %, the confidence interval, the mean relative standard deviation s r and the percentage error of determination, %.

12. Checking the analysis result

Carry out as described above.

Security questions

2. How to prevent hydrolysis of iron salts when dissolved in water?

3. Why, when gravimetric determination of iron, is a portion of the analyzed sample treated with a concentrated solution of nitric acid?

4. Give reasons for the choice of precipitant when determining iron in ferroammonium alum. How to calculate the optimal amount of precipitant?

5. What should be the precipitation conditions when obtaining iron(III) hydroxide as the precipitated form?

6. How to check the completeness of precipitation of iron(III) hydroxide?

7. Why, after the precipitation of an amorphous precipitate of iron(III) hydroxide, is the solution with the precipitate immediately diluted with water and only then filtered?

8. Why, after precipitation, the iron(III) hydroxide precipitate should be immediately separated from the mother liquor?

9. What filters are used to separate iron(III) hydroxide sediment?

10. How to prevent peptization of iron(III) hydroxide precipitate when washing it?

11. How to check the completeness of washing of the iron(III) hydroxide precipitate from the impurity of sulfate chloride ion?

12. How to obtain a gravimetric form from the precipitated form of iron(III) hydroxide?

13. Name the possible sources of systematic errors in the gravimetric determination of iron based on the mass of iron(III) oxide.

GOST 26318.3-84

Group A59

STATE STANDARD OF THE USSR UNION

NON-METAL ORE MATERIALS

Methods for determining the mass fraction of iron (III) oxide

Non-metallic ore materials.
Methods for determination of iron oxide mass fraction

OKSTU 5709

Valid from 01/01/86
until 01.01.96*
______________________________
* Validity limit removed
according to Protocol No. 5-94 of the Interstate Council
on standardization, metrology and certification.
(IUS N 11-12, 1994). - Note.

INFORMATION DATA

1. DEVELOPED AND INTRODUCED by the Ministry of Construction Materials Industry of the USSR

DEVELOPERS

N.M. Zolotukhina, V.M. Gorokhova, E.A. Pyrkin, O.N. Feodosyeva, E.I. Lopatina

2. APPROVED AND ENTERED INTO EFFECT by Resolution of the USSR State Committee on Standards dated October 31, 1984 N 3810

3. INSTEAD GOST 20543.3-75 and GOST 14328.2-77

4. REFERENCE REGULATIVE AND TECHNICAL DOCUMENTS

5. Validity period extended until 01/01/96 by Decree of the USSR State Standard dated 12/24/90 N 3242

8*. REISSUE (May 1991) with Amendments No. 1, 2, approved in October 1986, October 1990 (IUS 1-87, 4-91)
________________
*Numbering corresponds to the original. - Note.

This standard applies to feldspathic and quartzfeldspathic materials, mica, diopside and establishes photometric and complexometric methods for determining the mass fraction of total iron in terms of iron (III) oxide.

If disagreements arise in assessing the quality based on the mass fraction of iron (III) oxide, the determination is carried out using the photometric method.

1. GENERAL REQUIREMENTS

1. GENERAL REQUIREMENTS

1.1. General requirements for methods for determining the mass fraction of iron (III) oxide - according to GOST 26318.0-84.

2. PHOTOMETRIC METHOD

The method is based on the formation of an orange-red complex compound of divalent iron with orthophenanthroline or its analogues (dipyridyl or orthophenanthroline hydrochloride), stable for several hours.

2.1. Equipment, reagents, solutions

2.1.1. To carry out the analysis, use:

Photoelectrocolorimeter or atomic absorption spectrophotometer;

Hydrochloric acid according to GOST 3118-77, diluted 1:1 and 1:3;

Acetic acid according to GOST 61-75;

Tartaric acid according to GOST 5817-77;

Ascorbic acid;

Hydroxylamine hydrochloric acid according to GOST 5456-79;

Iron (III) oxide, dried at a temperature of 105-110 ° C to constant weight;

Sodium acetate according to GOST 199-78, solution concentration 70-100 g/dm;

Orthophenanthroline (or dipyridyl or orthophenanthroline hydrochloride);

Buffer solution pH 3.6 (33 g of sodium acetate is dissolved in water, 58 cm of glacial acetic acid is added and adjusted to 1 dm with water).

2.2. Preparing for analysis

2.2.1. Preparation of compound reagent

Place 400 cm of buffer solution, 20 g of hydroxylamine hydrochloride (or 5 g of ascorbic acid), 30 g of tartaric acid and 1 g of orthophenanthroline (or dipyridyl, or orthophenanthroline hydrochloride) into a measuring glass with a capacity of 1000 cm3, add water to the mark and mix. The solution is filtered into a bottle with a ground stopper.

(Changed edition, Amendment No. 1, 2).

2.2.2. Preparation of a standard solution of iron oxide

0.1 g of iron (III) oxide is placed in a glass with a capacity of 150 cm, 50 cm of hydrochloric acid diluted 1:1 is added, covered with a watch glass and kept in a boiling water bath until completely dissolved. The solution is cooled, transferred quantitatively into a 1000 ml volumetric flask, added to the mark with water and mixed.

1 cm of the resulting solution contains 0.1 mg of iron (III) oxide.

2.2.3. Construction of a calibration graph

The following are taken into volumetric flasks with a capacity of 50 cm: 0; 0.5; 1.0; 1.5; 2.0; 2.5 and 3.0 cm of a standard solution of iron (III) oxide, which corresponds to 0; 0.05; 0.10; 0.15; 0.20; 0.25 and 0.30 mg of iron (III) oxide.

20 cm of a solution of blank experiment 1 or 2 according to GOST 26318.1-84, 5 cm of the compound reagent are poured into the flasks, adjusted to the mark with a solution of sodium acetate and mixed. After 10 minutes, the solutions are photometered using cuvettes with a layer thickness of 10 mm and a blue light filter (400-500 nm) when using orthophenanthroline or orthophenanthroline hydrochloride and a green light filter (500-520 nm) when using dipyridyl. The reference solution is a solution that does not contain iron (III) oxide.

Based on the optical densities of solutions and the corresponding concentrations of iron (III) oxide, a calibration graph is constructed.

2.3. Carrying out analysis

2.3.1. From the analyzed solution 1 or 2 according to GOST 26318.1-84, an aliquot is taken into a 50 cm volumetric flask depending on the expected content of iron (III) oxide in accordance with Table 1.

Table 1

The same aliquot of the solution of blank experiment 1 or 2 is taken into another volumetric flask with a capacity of 50 cm3.

Then all the reagents are introduced into the flasks, as when constructing a calibration curve, adjusted to the mark with a solution of sodium acetate and mixed thoroughly. The optical density of the resulting test solution is measured relative to the blank solution.

From the measured optical density, the content of iron (III) oxide, mg, is determined from the calibration graph.

2.4. Processing the results

2.4.1. The mass fraction of iron (III) oxide () in percent is calculated using the formula

,

where is the mass of iron (III) oxide found from the calibration curve, mg;

Total volume of solution, cm;

The volume of an aliquot of the solution taken for analysis, cm;

Hitch weight, g.

2.4.2. The permissible discrepancy between the results of parallel determinations should not exceed the value given in table. 2.

Table 2

3. COMPLEXONOMETRIC METHOD

The method is based on the formation of a complex compound of ferric iron with sulfosalicylic acid and its destruction with Trilon B. The method is used with a mass fraction of iron (III) oxide of at least 1.5%.

3.1. Reagents and solutions

3.1.1. To carry out the analysis, use:

Hydrochloric acid according to GOST 3118-77, 1 M solution (80 cm of hydrochloric acid in 1 dm of aqueous solution);

Sulfosalicylic acid according to GOST 4478-78, solution concentration 100 g/dm;

Aqueous ammonia according to GOST 3760-79, diluted 1:1;

Trilon B according to GOST 10652-73, 0.025 m solution prepared from a standard titer containing 0.1 g/eq (0.1 mol) of the substance, which is dissolved in a 2 dm3 flask, added to the mark with water and mixed.

(Changed edition, Amendment No. 2).

3.2. Carrying out analysis

3.2.1. From the main solution 2, an aliquot of 50 cm is taken into a conical flask with a capacity of 300 cm. Add 0.3-0.5 cm of sulfosalicylic acid solution and diluted ammonia drop by drop until the color of the solution begins to change from purple to orange and immediately 5 cm of 1 M solution hydrochloric acid.

The solution is heated to 60-70 °C and titrated with Trilon B solution until the violet color disappears.

3.3. Processing the results

3.3.1. The mass fraction of iron (III) oxide () in percent is calculated using the formula

,

where is the volume of Trilon B solution consumed for titration, cm;

Total volume of the analyzed sample solution, cm;

0.001996 - titer of 0.025 M solution of Trilon B for iron (III) oxide, g/cm;

Volume of an aliquot of the solution taken for analysis, cm;

Hitch weight,

3.3.2. The permissible discrepancy between the results of two parallel determinations should not exceed the value given in Table 2.

(Changed edition, Amendment No. 2).

Some problems involve several chemical reactions. Moreover, it is often necessary to determine the excess and deficiency in each of them.

Problem 3.3.
Chlorine, released as a result of the interaction of 8.7 g of manganese (IV) oxide with 120 ml of 30% hydrochloric acid (p = 1.16 g/ml), reacted with iron weighing 2.8 g. The resulting salt was dissolved in 100 g water. Determine the mass fraction of salt in the resulting solution.
Given:
mass of manganese (IV) oxide: m(MnO 2) = 8.7 g;
volume of hydrochloric acid: V solution (HC1) = 120 ml;
mass fraction of HC1 in hydrochloric acid: (HC1) = 30%
density of hydrochloric acid: solution solution (HC1) = 1.16 g/ml;
iron mass: m(Fe) = 2.8 g;
mass of water: m(H 2 O) = 100 g.
Find: mass fraction of salt in the final solution.
Solution:
The problem statement describes several sequential chemical reactions.
1. Oxidation of chlorine from HC1 with manganese (IV) oxide:

MnO 2 + 4HC1 = MnC1 2 + C1 2 ^ + 2H 2 O

2. The chlorine gas formed in the first reaction is removed from the original solution and sent to another reaction vessel to react with metallic iron. It should be taken into account that it is oxidized to the oxidation state (+3).

3С1 2 + 2Fe = 2FeС1 3

The iron(III) chloride obtained in the second reaction is dissolved in water. The result is a new solution, in which it is necessary to determine the mass fraction of dissolved salt.

In this problem, we will have to determine the excess-deficiency twice: for the first and for the second equations. The solution algorithm can be represented by the following diagram:

1. Find the mass of hydrochloric acid and the mass of HC1 in it:

2. Find the amount of substance HC1 and MnO 2 that took part in the first reaction:

3. Determine which substance is in short supply in the first reaction.

Let us choose manganese (IV) oxide as a basis and determine from the reaction equation the amount of HC1 that is necessary to consume 0.1 mol of MnO 2.

n= 0.1 mol n= x mol
MnO 2 + 4HC1 = MnC1 2 + C1 2 ^ + 2H 2 O
n= 1 mol n= 4 mol

Let's make a proportion:
for 0.1 mol MnO 2 x mol HC1 should be consumed (according to the condition)
for 1 mole of MnO2, 4 moles of HC1 are completely consumed (according to the equation)
HC1 is necessary for complete consumption of all MnO 2.

HC1 is in excess and not all is consumed during the reaction. Therefore, further calculations according to the reaction equation will be carried out using MnO 2, since it is in short supply and is all consumed.

4. Based on the amount of MnO 2, we calculate the amount of substance C12 released in 1 reaction:

n= 0.1 mol n= x mol
MnO 2 + 4HC1 = MnC12 + C1 2 ^ + 2H 2 O
n= 1 mol n= 4 mol

Let's make a proportion:
0.1 mol MnO 2 gives x mol C1 2 (according to the condition)
1 mol MnO 2 gives 1 mol C1 2 (according to the equation)
x =0.1. 1/0.1 = 0.1 mol = n(C1 2)

5. According to the condition, all the chlorine released in 1 reaction interacted with iron. We find the amount of iron substance given by the condition:

6. Determine which substance is in short supply in the second reaction.

Let us choose chlorine as the basis and determine from the reaction equation the amount of Fe that is necessary to consume 0.1 mol C1 2.

n = 0.1 mol n - x mol
3С1 2 + 2Fe = 2FeС1 3
n = 3 mol n = 2 mol

Let's make a proportion:
for 0.1 mol C1 2 x mol Fe should be consumed (by convention)
for 3 moles of C12, 2 moles of Fe are completely consumed (according to equation)
x = 0.1. 0.2/ 3 = 0.667 mol Fe is required to completely consume all C1 2.

Iron is in short supply and is completely consumed during the reaction. Therefore, further calculations using the reaction equation will be carried out using it.

7. Based on the amount of iron substance, we determine the mass of the salt formed in the second reaction:
n = 0.05 mol m = x g
3С1 2 + 2Fe = 2FeС1 3
n = 2 mol n = 2 mol
M= 162.5 g/mol
m = 325 g

Let's make a proportion:
0.05 mol Fe gives x g FeC1 3 (according to condition)
2 mol Fe gives 325 g FeC1 3 (according to the equation)

8. Determine the mass fraction of FeCl 3 after dissolving it in 100 g of water:

Answer:(FeCl 3) = 7.5%.