When magnesium metal and an aqueous solution of hydrochloric acid combine, they produce an aqueous solution of magnesium chloride and hydrogen gas. Using the equation, Mg (s) + 2HCl (aq) arrow MgCl2 (aq) + H2 (g), if 48.6 g of Mg and 36.5 g of HCl are allowed to react, identify the limiting reagent.
Mg
HCl
MgCl2
H2

Question

When magnesium metal and an aqueous solution of hydrochloric acid combine, they produce an aqueous solution of magnesium chloride and hydrogen gas. Using the equation, Mg (s) + 2HCl (aq) arrow MgCl2 (aq) + H2 (g), if 48.6 g of Mg and 36.5 g of HCl are allowed to react, identify the limiting reagent.	
Mg	
HCl	
MgCl2	
H2

jfraser · Answer

use the amounts of the 2 reactants they give you, and figure out (using moles) which one will run out first

anonymous · Answer

36.5g of HCI ?

jfraser · Answer

why?

anonymous · Answer

i dont know its the least

jfraser · Answer

just because a reactant might weigh less than the other one doesn't make it the limiting reactant. 

Convert each of those masses into $moles$ using the molar masses of each and find out which one will run out first

anonymous · Answer

you find the molar mass on the periodic table right?

jfraser · Answer

right

anonymous · Answer

wait I got it, mg?

jfraser · Answer

why?

anonymous · Answer

i got 2.205 moles of mg and 4.110 moles of HCO since mg is less, its the limiting reaction

jfraser · Answer

it's not that simple

jfraser · Answer

you need to look at the balanced reaction, too

jfraser · Answer

each time this reaction "runs", 1 mole of Mg will use 2 moles of HCl

jfraser · Answer

you HAVE 2 moles of Mg and only 1 mole of HCl

jfraser · Answer

the molar mass of HCl is 36.5g, so you have 1 mole of HCl

jfraser · Answer

IDK where you're getting 4.1 moles of HCl from

anonymous · Answer

I'm so confused..

jfraser · Answer

you have 48.6g of Mg to start with, right?

jfraser · Answer

$$48.6g \space Mg * (\frac{1mol \space Mg}{24.3g \space Mg}) = 2 moles \space Mg$$

jfraser · Answer

and $$36.5g \space HCl * (\frac{1mol \space HCl}{36.5g \space HCl}) = 1mol \space HCl$$

jfraser · Answer

those are the starting amounts that the problem tells you that you start with

anonymous · Answer

So its HCI because in the ratio of 2:1

jfraser · Answer

HCl is the limiting reactant because it will run out first, yes

jfraser · Answer

even if there were 3 moles of HCl, do you see how it would still run out first?

jfraser · Answer

the balanced reaction says you NEED a ratio of Mg:HCl of 1:2

the problem GIVES YOU a ratio of Mg:HCl of 2:1

there't not enough HCl to react with all of the available magnesium

anonymous · Answer

ok thankyaa

jfraser · Answer

YW