Question

What mass of HBr (in g) would you need to dissolve a 2.7 −g pure iron bar on a padlock?

Answer 1

Answer: The amount of HBr required to dissolve a given amount of pure iron bar is 7.76 grams.

Explanation:

To calculate the number of moles, we use the equation:

$\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}$      .....(1)

Given mass of iron = 2.7 g

Molar mass of iron = 55.84 g/mol

Putting values in equation 1, we get:

$\text{Moles of iron}=\frac{2.7g}{55.84g/mol}=0.048mol$

The chemical equation for the reaction of HBr and pure iron follows:

$Fe(s)+2HBr(aq.)\rightarrow FeBr_2(aq.)+H_2(g)$

By Stoichiometry of the reaction:

1 mole of iron metal reacts with 2 moles of HBr

So, 0.048 moles of iron metal will react with = $\frac{2}{1}\times 0.048=0.096mol$ of HBr

Now, calculating the mass of HBr by using equation 1, we get:

Molar mass of HBr = 80.91 g/mol

Moles of HBr = 0.096 moles

Putting values in equation 1, we get:

$0.096mol=\frac{\text{Mass of HBr}}{80.91g/mol}\\\\\text{Mass of HBr}=(0.096mol\times 80.91g/mol)=7.76g$

Hence, the amount of HBr required to dissolve a given amount of pure iron bar is 7.76 grams.

Answer 2

The mass of HBr that would be needed to dissolve the 2.7 g pure iron bar is 7.8 g

To determine the mass of HBr that would be needed to dissolve the 2.7 g pure iron bar,

First, we will write a balanced chemical equation for the reaction

The balanced chemical equation for the reaction is

Fe(s) + 2HBr(aq) → FeBr₂(aq) + H₂(g)

This means,

1 mole of Fe is required to completely react with 2 moles of HBr

Now, we will determine the number of moles of Fe present in the 2.7g iron bar

Using the formula

$Number \ of\ moles = \frac{Mass}{Atomic\ mass}$

Atomic mass of Fe = 55.845 g/mol

∴ Number of moles of Fe present = $\frac{2.7}{55.845 }$

Number of moles of Fe present = 0.048348 mol

Since,

1 mole of Fe is required to completely react with 2 moles of HBr

Then,

0.048348 mole of Fe will completely react with 2 × 0.048348 mole of HBr

2 × 0.048348 = 0.096696 mole

∴ The number of moles of HBr required is 0.096696 mole

Now, for the mass of HBr that would be needed

From the formula

Mass = Number of moles × Molar mass

Molar mass of HBr = 80.91 g/mol

∴ Mass of HBr required = 0.096696 × 80.91

Mass of HBr required = 7.82367 g

Mass of HBr required ≅ 7.8 g

Hence, the mass of HBr that would be needed to dissolve the 2.7 g pure iron bar is 7.8 g

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