Determination of the equivalent mass of metal

Task: Determine the experimentally equivalent mass of the metal (magnesium, zinc – on the instructions of the teacher) by the amount of hydrogen released in the reaction of the interaction of the metal with hydrochloric acid

Me + 2HCl u003d MeCl 2 + H 2

Calculate its theoretical value and the relative experimental error.

Instruments and reagents. A device for determining the equivalent of the metal (Fig. 1.1.). Analytical scales. Thermometer. Barometer. Measuring cylinder for 25-50 ml. Chemical glass. Filter paper. Weight of metal (chemically pure) about 0.04 – 0.05 g. Hydrochloric acid (10 wt.% solution).

Definition progress.

1. Pour water through the funnel into the burette until zero division. Close the burette opening tightly with a stopper with a glass tube. Place a weighed portion of zinc into one part of the Landolt vessel. Fill the other part of the vessel through a funnel to two-thirds of the volume with diluted (10 wt.%) hydrochloric acid. Attach the vessel to the free end of the tube connected to the burette.

2. Check the tightness of the device. To do this, lower or raise the funnel with the ring by 10-15 cm. If the water level in the buret does not change, then the device is sealed and you can start the experiment. If the water level in the buret changes, then it is necessary to close the burette and the vessel with stoppers more tightly, check again, etc. Record the water level V 1 in the burette before the start of the experiment with an accuracy of 0.1 ml.

3. Bring the acid and metal into contact by gently tilting the Landolt vessel. After complete dissolution of the metal, wait 5-7 minutes for the contents of the vessel to cool. Then set the water level in the burette and funnel at the same height. In this case, a pressure equal to the pressure of the outside air is created inside the device. Record the water level V 2 in the burette after the experiment.

4. Enter the results of the experiment in the journal in the form:

Metal weight, m, g………………………………………………………..

Water level in buret:

up to experience V 1 , ml………………………………………………..

after experience V 2 , ml…………………………………………..

The volume of released hydrogen V H2 , ml………………………………..

The volume of hydrogen under normal conditions (n.o.) V 0 , ml………………

Experiment temperature T = 273+t, K…………………………………………

Barometric pressure P, mm Hg…………………………………..

Saturated water vapor pressure h, mm Hg at test temperature…

Experimental equivalent mass of metal М e exp , g/mol……….

Theoretical equivalent mass of metal M e theor , g/mol……………..

Relative error e, %………………………………………….. ………………………….

Rice. 1.1. The device for determining the equivalent of the metal:

1) Burette for measuring the volume of released hydrogen;

2) Landolt vessel for carrying out the reaction;

3) Rubber tube;

4) Funnel.

2.2. Calculations:

1. Calculate V H2 displaced hydrogen from the level difference in the burette:

V H2 u003d V 2 -V 1

2. Bring this volume to normal conditions:

See the value of h in the reference book. The correction h is introduced due to the fact that the total pressure on water is the sum of the partial pressures of hydrogen and water.

3. Calculate the experimental mass of the metal:

where is the equivalent volume of hydrogen, equal to 11200 ml/mol.

4. Compare the experimentally found equivalent mass of metal (M e )

with theoretically calculated M E theor u003d A / B, calculating the error of the experiment as a percentage:

2.3. Control questions and tasks

1. Calculate the molar mass equivalents of the following elements:

a) magnesium, if it is known that when one mole of it is heated in a stream of oxygen, the mass increased by 66.7%. Answer: 11.9 g/mol;

b) tin, if when 0.9185 g of it is heated in a stream of oxygen, 1.166 g of tin oxide is formed. Answer: 29.68 g/mol.

2. Determine the molar mass of the element’s equivalent, if the reduction of 1.3 g of the oxide of this element with aluminum resulted in 1.02 g of aluminum oxide containing 47% oxygen. Answer: 13.66g/mol.

3. Write the formula for the compound of antimony with sulfur, if it is known that the molar mass of antimony atoms is 121.8 g / mol, its equivalent mass is 40.6 g / mol, the molar mass of sulfur atoms is 32 g / mol, the equivalent mass is 16 g / mol.

4. Determine the molar masses of equivalents and equivalence factors of acids and bases in the following reactions:

a) HNO 3 + Bi(OH) 3 = Bi(0H) 2 NO 3 + H 2 O;

b) H 2 S + NaOH = NaHS + H 2 O;

c) 3H 2 SO 4 + 2А1(OH) 3 = Al(SO 4 ) 3 + 6H 2 O;

d) H 3 PO 4 + Ca (OH) 2 u003d CaHPO 4 + 2H 2 O;

e) 2HCl + Bi(OH) 3 = BiOHCl 2 + H 2 0.

5. Calculate the molar mass of the equivalent and the equivalence factor of potassium chromate K 2 CrO 4 as an oxidizing agent, if K 2 CrO 4 is reduced to KCrO 2 .

6. Determine the molar mass of the metal equivalent if 0.34*10 -3 kg of it is displaced from the acid by 56.94*10 -6 m 3 of hydrogen at a temperature of 0°C and a pressure of 94643 Pa. Answer: 67.8 g/mol.

7. Determine the molar mass of the metal equivalent in the following compounds:

Mn 2 O 7 , Mg 2 P 2 O 7 , Cr 2 O 3 , Ba (OH) 2 , Al 2 (SO 4 ) 3 * 18H 2 O, Ca 3 (PO 4 ) 2 , Ag 2 O, FeSO 4 • 7H 2 O, CrPO 4 .

8. What is the equivalent volume of oxygen?

9. When 2.5 g of metal carbonate interacted with nitric acid, 4.1 g of nitrate of the same metal was formed. Calculate the molar mass of the metal and the metal equivalent.

Table of contents

LABORATORY WORK №1. one

Molar masses of equivalents of oxides in exchange reactions : 3

Molar masses of acid equivalents in exchange reactions : 3

Molar masses of base equivalents in exchange reactions : 4

Molar masses of salt base equivalents in exchange reactions : 4

Me + 2HCl u003d MeCl 2 + H 2 6

Definition progress. 6

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