Question

How to find the moles of hydrogen . I know my limiting reagent is Mg that weighs 0.03g. it has a 1:1 mole to mole ratio.

Mg(s)+2HCl(aq)--> H2+MgCl(aq)​

Answer 1

0.0012 moles

Step-by-step explanation:

Data Given:

mass of Mg = 0.03

moles of Hydrogen = ?

Reaction given:

Mg(s) + 2HCl(aq) -------> H₂ + MgCl₂(aq)​

Solution:

Now first look at the reaction

Mg(s) + 2HCl(aq) -------> H₂ + MgCl₂(aq)​

1 mol 1 mol

from the reaction its known to us that the mole ratio of Mg to hydrogen is 1:1

Now

Convert moles to mass

As,

Molar mass of Mg = 24.3 g/mol

Molar mass of H₂ = 2(1) = 2 g/mol

So,

Mg(s) + 2HCl(aq) -----------> H₂ + MgCl₂(aq)​

1 mol(24.3g/mol) 1 mol(2 g/mol)

24.3 g 2 g

So, we come to know that

24.3 grams Mg gives 2 g of H₂ then how many grams of H₂ will be produce by 0.03 g of Mg.

Apply Unity formula

24.3 grams Mg ≅ 2 g of H₂

0.03 grams Mg ≅ X g of H₂

Do cross multiplication

grams of H₂ = 0.03 g x 2 g / 24.3 g

grams of H₂ = 0.0025 g

So,

0.03 g of Mg gives 0.0025 g of hydrogen

Now Convert mass of hydrogen to moles

Use mole formula

no. of moles = mass in grams / molar mass

Put values in above formula

no. of moles = 0.0025 g / 2 (g/mol)

no. of moles = 0.0012 mol

So,

moles of hydrogen = 0.0012 moles