How many moles of aluminum are required to react completely with 18 moles of H2SO4?

Expert Answers
sharikendrick eNotes educator| Certified Educator

Step 1: Write the balanced reaction between Al and `~H_2SO_4` .

The balanced equation for this reaction is:

`~2Al` + `~3H_2SO_4` -> `~Al_2(SO_4)_3` + `~3H_2`

Step 2: Determine the given amount, unit, and substance.

The given amount, unit, and substance is: 18 moles of `~H_2SO_4` .

Step 3: Determine the final unit and substance.

The final unit and substance is: moles of Al.

Step 4: Determine the ratio of moles of Al to `~H_2SO_4` .

The ratio of moles between two substances can be described by the coefficients of the substances in the reaction. The coefficient of Al in the reaction is 2. The coefficient of `~H_2SO_4` in the reaction is 3. Therefore, the ratio of Al moles to `~H_2SO_4` is 2 to 3. 

Mole ratios can be written as fractions:

    2 moles Al/3 moles `~H_2SO_4`  OR  3 mole `~H_2SO_4` /2 moles Al

Step 5: Set up the calculation.

The calculation will take the general form:

    given amount x mole ratio

    18 mol `~H_2SO_4 ` x (2 moles Al/3 moles `~H_2SO_4`) = 12 mol of Al

Notice that the mole ratio is oriented such that moles of `~H_2SO_4` is on the bottom. This way, moles of `~H_2SO_4` cancel out and we are left with moles of Al.


johan15 | Student

The first step in answering this question is to first determine the reaction between the two reactants. The complete balanced reaction between sulfuric acid and aluminium is as follows: 

2Al + 3H2SO4 -----> Al2(SO4)3 + 3H2

Now that we have completed step 1 by determining a balanced equation. We can now move to step 2. Step 2 requires finding the molar ratio between the two reactants.

In the above reaction, the molar ratio of aluminium to sulfuric acid is as follows: 

Al : H2SO4

2 : 3

Now that we have determined the molar ratio of the reactants in our reaction, we can move on to step 3. 

Step 3 requires us to determine the number of moles of aluminium that is required to completely react with 18 moles of sulfuric acid. We will use the molar ratio to determine this. This is determined as follows: 

Number of moles of Aluminium = 18 moles H2SO4 * ( 2 moles Al / 3 moles H2SO4) 

Number of moles of Aluminium = 12 moles Al

In order for sulfuric acid to completely react with the aluminium, 12 moles of aluminium is required.