Determining the Molar Mass of Carbon Dioxide

Topics: Mass, Atomic mass unit, Molar mass Pages: 5 (1616 words) Published: June 1, 2013
Determining the value of molar mass of chosen compound

Marta Dürrigl 1mmA

Chemical reaction:
b.)CaCO3 (s) + 2HCl (aq) ----------- CaCl2 (aq) + CO2 (g) + H2O(l)

The aim of this investigation is to experimentally determine the molar mass of carbon dioxide (CO2) by measuring its volume and calculating its mass. CO2 which we will measure will arise as a product of a chemical reaction between Calcium Carbonate (CaCO3) and Hydrochloric acid (HCl) as it is shown in the chemical equation above. Once we find out the volume of the compound which molar mass we want to determine, it will be easy to calculate the number of moles by using the following formula; pV=nRT

* p is pressure in Pa,
* V is volume in m3,
* n is molar quantity in mol,
* R is gas constant of 8.314 J/Kmol
* T is temperature in K.
In addition we need to find out the mass of CO2 to be able to calculate its molar mass using the second formula M=m/n
* M is a molar mass with the measuring unit grams per mole (g/mol) * m is a mass of a compound in grams (g)
* n is a number of moles(mol)

By measuring the volume and calculating the mass of CO2 we will be able to determine its molar mass. We can predict that the molar mass of CO2 is going to be 44.01 g/mol because the molar mass (M)as a number equals the relative molecular mass (Mr) which is a sum of relative atomic masses (Ar) of all the elements in the compound. Relative atomic mass values we can find in periodic system. (Ar)of C is 12.01 and the (Ar) of O is 16. This molar mass is theoretically stated and we do not expect it to change. HYPOTHESIS (2):

Molar mass is the ratio between mass of a compound and its number of moles. Number of moles of a gaseous compound can be determined by measuring its temperature, pressure and volume and calculated by the following expression: pV=nRT which means that n=pV/RT

In this experiment we will use the chemical reaction between CaCO3 and HCl to produce CO2. When mixing CaCO3 in a solid state with a solution of HCl in the beaker a solution of CaCl2 in water will stay in the beaker while CO2 will move through a pipe in a measuring cylinder placed in another beaker filled with water. This measuring cylinder will be turned upside down and thus completely filled with water. When CO2 enters the cylinder since it has a lower density then the water it will move to the top of the cylinder displacing the water. The volume of the displaced water is equal to the volume of the gas produced in the reaction. To find out the mass of CO2 we will use the idea of conservation of mass which says that mass can be neither created nor destroyed so that a chemical reaction that changes a properties of substances leave their total mass unchanged. In other words knowing the chemical equation CaCO3(s) + 2HCl (aq) ----------- CaCl2 (aq) + CO2 (g) + H2O (l) we can expect that the total mass of substances entering the reaction equals the total mass of products of this reaction. So we will measure the mass of CaCO3 and HCl before the reaction and the mass of the substance in the beaker after the reaction (CaCl2 (aq) + H2O (l)) assuming that the difference will be a mass of CO2 which will have passed through the pipe to the measuring cylinder. Knowing the mass of CO2 and number of moles we can easily determine its molar mass.

Materials and chemicals that we're going to use in this experiment * beaker of 400 mL
* thermometer
* barometer
* measuring cylinder of 100mL
* glass pipes
* Erlenmeyer flask of 250 mL
* Rubber stopper for Erlenmeyer flask with two holes in the middle * analytical balance
* 50 g of CaCO3
* 225 mL of about 6 mol/ L HCl*
*obtained by dilution of concentrated HCl with deionized water in 1:1 ratio METHOD (1):
First step in our method is to measure the mass of substances entering the chemical reaction. For the measurement we will use the analytical...
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