We did a lab to find the atomic mass of Magnesium. We used an eudiometer and HCL and a mg ribbon.
Explain in terms of moles, limiting reactants and experimental feasibility, why we use concentrated HCl (12M) instead of 1M or 6M??
Would the calculated atomic mass be higher, lower, or the same as the expected value if you ignored the vapor pressure of water?
The use of concentrated HCl (12M) instead of lower concentrations like 1M or 6M in the lab experiment to find the atomic mass of magnesium can be explained in terms of moles, limiting reactants, and experimental feasibility.
1. Moles: Concentrated HCl contains a higher concentration of HCl molecules per unit volume compared to lower concentrations. This means that a higher number of moles of HCl are available for the reaction with the magnesium.
2. Limiting reactants: In this experiment, the limiting reactant is the one that is completely consumed and determines the amount of product formed. By using concentrated HCl, we ensure that the limiting reactant is the Mg ribbon rather than the HCl. This is because the higher concentration of HCl allows for a greater number of collisions between the HCl molecules and the Mg ribbon, ensuring that the Mg ribbon reacts completely and is not the limiting factor in the reaction.
3. Experimental feasibility: Concentrated HCl is used for practical reasons. It is more efficient and time-saving to use a higher concentration of HCl since it requires a smaller volume to react with the magnesium ribbon. This reduces the amount of time needed for the reaction to occur and simplifies the measurements required for the experiment.
Regarding the calculated atomic mass of magnesium in relation to the expected value if the vapor pressure of water is ignored, it would be higher. This is because when the reaction occurs between magnesium and HCl, it produces hydrogen gas (H2) and magnesium chloride (MgCl2). If the vapor pressure of water is ignored, the produced hydrogen gas would not be taken into consideration. As a result, the measured mass of magnesium would appear higher since the contribution of the hydrogen gas (combustion product) is disregarded. Thus, the calculated atomic mass of magnesium would be slightly higher than the expected value if the vapor pressure of water is not taken into account.
To understand why concentrated HCl is used instead of 1M or 6M for the lab experiment, we need to consider moles, limiting reactants, and experimental feasibility.
When a reaction occurs, it is important to have a sufficient amount of one reactant to fully react with the other reactant. This is known as the limiting reactant. In this case, the limiting reactant is the magnesium (Mg) ribbon, as it is much less abundant compared to the HCl.
Concentrated HCl (12M) contains a higher concentration of HCl molecules per unit volume compared to 1M or 6M solutions. This means that by using concentrated HCl, we are adding a larger number of HCl molecules to react with the limited amount of magnesium. This increases the likelihood of the magnesium ribbon completely reacting, ensuring a more accurate determination of the atomic mass of magnesium.
Moreover, using concentrated HCl also enhances the feasibility of the lab experiment. The reaction between magnesium and hydrochloric acid produces hydrogen gas, which is collected in the eudiometer. By using concentrated HCl, a larger volume of hydrogen gas is generated, making it easier to measure and calculate the amount of gas produced accurately. This helps improve the precision of the experiment.
Now, moving on to the effect of ignoring the vapor pressure of water on the calculated atomic mass of magnesium. In this experiment, water vapor is also present in the eudiometer due to the reaction between magnesium and HCl. Ignoring the vapor pressure of water would lead to an overestimate of the atomic mass of magnesium.
Water vapor exerts a partial pressure in the eudiometer, which affects the total pressure of the gas collected. Ignoring the vapor pressure of water would result in an overestimation of the total pressure. This, in turn, affects the calculated atomic mass of magnesium since it is obtained using the ideal gas law, which relies on the accurate measurement of pressure.
As a result, if the vapor pressure of water is ignored, the calculated atomic mass of magnesium would be higher than the expected value. It is important to consider the vapor pressure of water and make appropriate adjustments to obtain a more accurate estimation of the atomic mass of magnesium.