M7 (Limiting Reactant Fundamental Exercise)

[Christine Nguyen 3D]

Solid boron can be extracted from solid boron oxide by reaction with magnesium metal at a high temperature. A second product is solid magnesium. (a) Write a balanced equation for the reaction. (b) What mass of boron can be produced when 125 kg of boron oxide is heated with 125 kg of magnesium?

My question is: are we expected to know how to write out the full chemical reaction for part (a) using a periodic table and if so, how would I know what it would look like without looking it up online? I was never taught what 'oxide' meant either and didn't know if that was important. From there I could probably figure out part (b)!

Thanks!

[Melody Haratian 2J]

Hi! Oxide is usually used to name a compound that has an oxygen in it. Since the compound is boron oxide, it has both boron and oxygen in it. Using the periodic table, we see that boron has a charge of 3+ while oxygen has a charge of 2-, so we need 2 borons and 3 oxygens to have a balanced compound. Thus, the formula for Boron oxide is B2O3. To find the chemical equation, we know that B2O3 reacts with Mg and releases B. The second product formed is MgO, since Mg attaches to the O in B2O3.

The unbalanced chemical equation is:
B2O3 + Mg——-> MgO + B
Then from there be sure to balance the chemical equation for part b.
I hope this helps!

[Hannah Rim 2D]

Hi! Yes, I'm pretty sure that we will have to know how to write out full chemical equations using just the periodic table. I personally solve it this way:

In this word problem, the question states that solid boron can be extracted from solid boron oxide. Solid boron is just "B" and solid boron oxide is "B2O3" (We know that boron oxide is B2O3 because oxide refers to oxygen). The word "extraction" implies that solid boron will be on the products side. Furthermore, the question also states that boron oxide is reacting with magnesium metal. This reveals that boron oxide and magnesium will for sure be on the reactants side.

When boron oxide reacts with magnesium, boron and magnesium oxide is the product. We know this because it follows the model of a single replacement reaction (A+BX ---> B+AX)

In the context of this problem, the unbalanced chemical equation would be Mg+B2O3 ---> B+MgO. After balancing, the chemical equation would be 3Mg +B2O3 ---> 2B+3MgO. Using this final equation, we can find the answer to part b! I hope it helped (:

[Christine Nguyen 3D]

Thank you both!! Really cleared it up for me <333