posted by .

Suppose you tried to combine 42 grams of magnesium with 42 grams of oxygen.

Which of the two substances would have some left after the reaction and how much magnesium oxide would be formed?

  • chemistry -

    Limiting reagent problems are done alike.
    1. Write and balance the equation.
    2Mg + O2 ==> 2MgO

    2. Convert grams to moles.
    a. 42 grams oxygen/32 = 1.31 moles O2.
    b. 42 grams Mg/24.305 = 1.73 moles Mg.

    3. Using the coefficients in the balanced equation, convert moles in 2a and 2b to moles of the product.
    a. from O2: moles MgO = 1.31 moles O2 x (2 moles MgO/1 mole O2) = 1.31 x 2 = 2.62 moles MgO formed.
    b. from Mg: moles MgO = 1.73 moles Mg x (2 moles MgO/2 moles Mg) = 1.73 x 2/2 = 1.73 moles MgO formed.
    c. USUALLY, moles of the product from a and from b are different, as they are in this case. You know both answers can't be right. Which one is right? The smaller value is ALWAYS the correct value AND THE MATERIAL PRODUCING THAT NUMBER IS THE LIMITING REAGENT (in this case Mg).

    4.a. If the problem asks (this one does in the last part) for grams MgO formed, that's just the smaller value x molar mass; i.e., 1.73 moles MgO x molar mass MgO = grams MgO.
    b. If the problem asks which reactant is left over, you have that information in step 3. The limiting reagent is Mg; therefore, oxygen must be the material left.
    c. Some of these problems (this one doesn't) asks for how much of the "other" material is left over? You do that exactly as in step 3.
    moles O2 used = 1.73 moles Mg x (1 mole O2/2 mols Mg) = 1.73/2 = 0.865 mols O2 used. We had 2.62 initially - 0.865 moles used = 1.75 moles O2 remaining un-reacted. You can conert that to grams by 1.75 g O2 x molar mass O2 = ??

    You need to go through this again and assign good numbers to each part. I've rounded here and there and estimated at some other spots. Put this procedure somewhere so you can refer to it later.

  • chemistry -

    When one pound of gasoline (made up of compounds of hydrogen and carbon) is burned in an automobile approximately 3 pounds of carbon dioxide, CO2, is given off. Carbon dioxide is one of the gases contributing to global warming. What information from this experiment helps explain how one pound of gasoline can give off approximately 3 times an much CO2?

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. science

    these are my homework questions can you answer any?
  2. Chemistry

    Magnesium reacts with oxygen to form magnesium oxide according to the following equation: 2Mg(s) + O2(g) ==> 2MGO(s) If 0.81 grams of magnesium oxide are formed, how many grams of oxygen reacted?
  3. Chemistry

    Suppose you tried to combine 42 grams of magnesium with 45 grams of oxygen. Which of the two substances would be left after the reaction?
  4. Chemistry

    A 4.5 g piece of magnesium ribbon undergoes combustion in air to produce a mixture of two ionic solids, MgO and Mg3N2. Water is added to this mixture. It reacts with the magnesium oxide to form 9.97 g of magnesium hydroxide. Assume …
  5. Chemistry

    Calcium carbonate is insoluble in water. Name two substances that when mixed in solution, will form a precipitate of calcium carbonate. Explain why is it the two substances that you have chosen. ¬†why does magnesium chloride cannot …
  6. science

    what will be the law of conversion of a) 65 grams 70 grams b) magnesium + oxygen = magnesium oxide 45 grams ?
  7. Chem 2

    If we burn a strip of magnesium in air, there will be two main products, magnesium oxide and magnesium nitride. If we then treat that mixture with water, the nitride ion is converted to ammonia. After boiling away the water and ammonia, …
  8. chemistry

    A piece of magnesium weighing 48 grams is burned in air n 80 gram of magnesium oxide is formed. what mass of oxygen combined with the magnesium is in the reaction?
  9. Chemistry

    How many grams of magnesium oxide could be formed from the reaction of .248g of magnesium metal?
  10. Chemistry

    4.13 grams of magnesium chloride were recovered after the chemical reaction between magnesium and chlorine gas occurred. If 7.10 grams of magnesium chloride was suppose to be produced, what is the percent yield of magnesium chloride?

More Similar Questions