Lab Report- Which alkali metal carbonate PDF

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ABSTRACT The purpose of this experiment is to figure out the alkali metal present by conducting three different methods of experiments. The unknown alkali metal was Sodium with a molar mass of .0493 mol Na. INTRODUCTION The purpose of this experiment is to figure out the alkali metal present by conducting three different methods of experiments. The alkali metal present turned out to be Sodium. Some of these methods included the gravimetric analysis, simple weight loss, and the flame test. Method one (Gravimetric Analysis) is conducted to determine the gravimetric analysis which involved isolating barium carbonate by using reaction stoichiometry and then weighing it and determining the molar mass. The balanced equation for Method 2 (Simple Weight Loss) is M2CO3+2HCl----->CO2+2MCl+H2O. Method 2 took advantage of the principle of conservation of mass theory by taking metal carbonate and reacting it with an acid-base to produce a gas (CO2). This law of conservation was implemented to determine the amount of CO2 involved. Method 3 (Flame Test) involved heating toothpicks with the unknown carbonate and figuring out which alkali metal it was depending on the color of the flame. DATA Number 1 Unknown Alkali Metal Table 1: Method 1:Gravemetric Analysis

Mass Of empty beaker (g)

50.472 (g)

Mass of beaker + unknown M2CO3 (g) 

51.042 (g)

Mass of unknown M2CO3 (g)

0.57 (g)

Mass of watch glass with filter papers (g) (2 pieces)

42.302 (g)

First mass of dried precipitate + watch glass + filter papers (g)

43.783 (g)

Second mass of dried precipitate + watch glass + filter papers (g)

Ran out of time, explanation within discussion

Difference between 1st and 2nd masses (g)

Ran out of time, explanation within discussion

Third mass of the dried precipitate + watch glass + filter papers (g)

Ran out of time, explanation within discussion

Mass of Ba2CO3 (g)

1.135 (g)

Table 2:Method 2: Simple Weight loss Analysis

Trial #1

Trial #2

Trial #3

Average

Mass of clean empty beaker (g)

A 5 0.629g

50.629g

50.629g

50.629

Mass of unknown M2CO3(g)

B= 51.101g

51.135g

51.532g

51.256

Mass of unknown M2CO3 + beaker (g)

C=B-A 0.472

0.506

0.562

0.513

71.35

72.84

71.87

Mass of graduated D 71.420 cylinder + 20.0mL HCl (g) Mass of graduated cylinder after delivering HCl (g)

E 5 2.23

52.26

52.022

52.171

Actual mass of HCl (g)

F=D-E 19.19

19.09

20.818

59.098

Final mass of beaker after the reaction (g)

G 7 1.9

71.354

71.824

71.692

Mass of products in the beaker (g)

H=G-A 2 1.3

19.7

21.2

20.73

Mass CO2 produced (g)

C+F-H -1.64

-.124

.18

-.528

Flame Test Method 3: Observations: When putting the metal carbonate in the flame the color that resulted was golden-yellow. When looking at the table in the manual it is determined that the element responsible for this coloration is Sodium (Na). RESULTS Method 1 Molar mass of BaCO3= 197.34g/mol Mass of dry solid= 1.135 Mass of unknown solid= 0.57 1.135gBa2CO3/197.34gBaCO3=.00575

MM of M2CO3= 0.57gM2CO3/0.00575mol=99.13g/mol Molar mass of Li2CO3: 73.89 g/mol Molar mass of Na2CO3: 105.99 g/mol Molar mass of K2CO3: 138.21 g/mol The calculations show that the unknown carbonate is closer in mass to Sodium carbonate which is accurate to what was originally thought. Method 2 Average Mass of CO2 produced= -5.28 MM of CO2 # of mol of CO2=-5.28/44.01= -0.011997mol CO2 MM of M2CO3=0.518/-0.011997= -42.761g/mol Molar mass of Li2CO3: 73.89 g/mol Molar mass of Na2CO3: 105.99 g/mol Molar mass of K2CO3: 138.21 g/mol The calculations show that the unknown carbonate is closer to Lithium carbonate, but these calculations are obviously wrong because it should be impossible to get negative g/moles. These errors are due to incorrect measurements within the experiment. Method 3 The flame test indicated that the unknown carbonate is Sodium because of the golden-yellow coloration. This result supports our hypothesis of the substance being Sodium.

DISCUSSION The purpose of this experiment was to find the unknown alkali by using three different methods to find the atomic mass and then comparing them to Li2CO3, Na2CO3, and K2CO3 to find out which compound the unknown is. For the Gravimetric analysis method we ran out of time and did not have enough time to weigh the masses of the second and third precipitates, therefore, the difference between the two masses couldn’t be found. For methods 1 and 2, it is very important to accurately measure the substances and this was probably where the error occurred. The CO2 average turned out to be a negative number which is theoretically impossible in this experiment. The molar mass for method 1 was 99.13 which is closer to Sodium Carbonate. Method 2 has a molar mass of -42.761 which is not accurate at all considering that there was an error somewhere along the experiment. The flame test confirmed that the unknown was sodium since the color or the flame turned into a golden-yellow color. Method 1 gave more reliable results when doing the calculations, but if method 2 was performed accurately, the experiment would have been more accurate because it was performed three times....