Chemistry

posted by .

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

  • Chemistry -

    If I interpret the question correctly, for #1, you can read the volume vs grams Mg. Convert that to volume vs 1 g Mg. A simple proportion will do it.
    2. Same thing for #2 EXCEPT change the 1 g to 24.32 g (I think that's the atomic mass of Mg). I wouldn't make a straight multiplication of what I had found for 1 g because of rounding errors but read from the graph and convert to the molar mass from the mass you read.
    #3. Do that for Zn. The volume/mole should be the same (but the volume/gram will not be the same).

  • Chemistry -

    For example, if I pick a point at random on the graph.. say (0.200, 184.3).

    Then
    R1 = volume H2 / mass Mg
    R1 = 184.3 mL H2 / 0.200 g Mg
    R1 = 921.5 mL H2 / g Mg

    for the next part it says "using the value of R1" so...

    R2 = (184.3 mL H2 / 0.200 g Mg) * (1 mol Mg / 24.31 g Mg)
    R2 = 37.90621144 mL H2 / mol Mg
    R2 = 37.91 mL H2 / mol Mg

    then do essentially the same thing for R3 and make the comparison between R2 and R3.

  • Chemistry -

    would i get a more accurate answer using the slope instead of a point at random?

  • Chemistry -

    Won't the line be a straight line as long as you haven't reached the limiting reagent part. I think you want the point. You may want to pick two or three points and use the average.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Chemistry

    We did a lab for acid-base titrations, and I'm having trouble with my post lab questions because I had trouble with acid-base reactions and titrations in the first place! "Calculate the molar amounts of NaOH used in the reaction with …
  2. Chemistry

    Completion Whenever quantities of two or more reactants are given in a stoichiometric problem, you must identify the _____. This is the reagent that is completely ______ in the reaction. The amount of limiting reagent determines the …
  3. Lab in general

    I just read my syllabus for lab and I am kind of shocked at what it says. I do know that I have to write out procedures of the lab in my nbk before coming to lab but I just read that it says "You will NOT be allowed to refer to you …
  4. Chemistry

    Can someone please help me on this two Chemistry questions...they are from my lab....the lab was on Acids and Bases using Red Cabbage Indicator. Q1- How consistent was the cabbage juice indicator for this lab?
  5. Biology

    I had a Bio lab about gel electrophoresis and PCR. for each lab, we have to make up thoughtful, detailed questions. You don't have to answer the questions so please don't go through the trouble by answering them. The first question …
  6. chemistry

    I did a lab on pressure and depth today. This lab was to simply submerge a plastic tube into a large graduated cynlinder to find the relationship between the two. I found that as the depth increases, so does the pressure. One of the …
  7. Chemistry: Bunsen Burner Lab

    Hi! I have recently completed a bunsen burner lab and need help with a few conclusion questions: 1) What kind(s) of energy is released by the reaction of fuel and air in this system?
  8. Chemistry lab

    In my lab class I am having to write a lab experiment and preform it tomorrow. It deals with specific heat of unknown metal and density. the first part you have boil water with the metal in it, and then put it in a cup and measure …
  9. Chemistry Lab

    In chemistry we are doing a lab that involves crucibles and Mg ribbon, we have three days to complete the lab. Anyways do you think it would be alright to substitute the mass of the crucible we had the first day with the mass of the …
  10. Chemistry

    Hi, I have few questions from a chemistry lab that i did, 1) I'm not sure whats the point of heating a nitrate (NaNO3) 2) I'm not sure why you add NaOH to NaNO3 after it has dissolved in water 3) I'm not sure why do we have to test …

More Similar Questions