Jeff and jill go canoeing. while reaching to feed a duck, the boat flips. jeff and jill blow up their inflatable life preservers and then put them on. as they wait for the rescue squad, they calculate how much nitrogen is in each life preserver. they estimate that the volume is 17 l, pressurized to 1.3 atm at 298◦k. the air used for inflation is 80% nitrogen by volume and 20% oxygen by volume. give the amount of nitrogen gas. answer in units of grams.

20 grams? 30 grams? 40 grams?

First, you will have to write out and balance the equation, so:

Because we’re looking at a single element reacting with an acid, we know that the reaction must be a single replacement.

Mg + HCl —-> MgCl2 + H2

We use H2, because hydrogen can only exist by itself when covalently bonded to itself, in a diatomic state.
Mg has an oxidation state of +2, while Cl has an oxidation state of -1. Therefore, you need 2 Cl to cancel the charge fully.

Now it needs to be balanced, so you get:

Mg + 2HCl —-> MgCl2 + H2

Now we have molar ratios to do our conversions

So we’ll use stoichiometry to find the theoretical yield for both reactants, and whichever one is the LEAST is the answer.

(32.5g Mg) (1mol/24.3g) (1mol MgCl2/1 mol Mg) (95.3g/1 mol MgCl2) = 127.5g

(32.5g HCl) (1mol/36.5) (1mol MgCl2/2mol HCl) (95.3g/1 mol MgCl2) = 42.4g

So, you will get 42.4 g of MgCl2