June 29, 2016

Homework Help: Chemistry

Posted by Jake on Wednesday, March 11, 2009 at 11:17pm.

I'm about to do the second part of a Limiting Reagent laboratory tomorrow. There are a few questions that are giving me trouble on the pre-lab assignment.

In the first lab period, we measured the amount of H2 gas produced in a reaction of Mg and 10 mL of 2.0 M HCl. We varied the mass of Mg, starting at 0.050 g and increasing by increments of 0.050 g up to 0.400 g.

With the data collected, we constructed a graph of volume of H2 gas produced (mL) vs. mass of Mg (g). We had to include a best fit line in the linear portion of the graph.

An analysis of the graph shows that as the mass of Mg increases, the volume of gas increases proportionally until Mg is no longer the limiting reagent. Once 2.0 M HCl becomes the limiting reagent, the graph becomes almost vertical since this amount of H2 gas is the maximum amount that can be produced in the reaction.

What I'm required to do is this:

Using your graph,

*** 1. Determine the value R1 (volume of H2 gas produced per gram of Mg that reacts).

*** 2. Using the value of R1, determine the value R2 (volume of H2 gas produced per mole of Mg that reacts).

*** 3. At a given temperature and pressure, the volume of a gaseous sample is directly proportional to the moles of gas (Volume = C * moles, where C is a constant). Assuming that the temperature and pressure is the same for the reaction of magnesium with HCl and zinc with HCl and considering the balanced chemical equations for these reactions, answer the following question: What is the relationship between the factor R2 and the factor R3 (volume of H2 gas produced per mole of zinc that reacts)?

The balanced chemical equations are:

Mg + 2HCl --> H2 + MgCl2
Zn + 2HCl --> H2 + ZnCl2

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