Quick Question!

[zibb3r]

Hi guys,  I wasn't sure what answer I should pick for this question (MC):

Biodiesel is made by a process called base-catalysed transesterification.  Here a triglyceride such as canola oil is reacted with methanol using NaOH as a catalyst.  Methyl esters are formed.  The by product of this process is:

a)H₂O
b)C₃H₈O₃
c)C₂H₅OH
d)C₆H₁₂O₆

I wasn't sure what to pick!  Aren't both Water (a) and Glycerol (b) produced???  So do I go (a) or (b)

Thanks

[oneoneoneone]

I think the main by product is glycerol, since you kind of use water as a reactant (hydrolysing the triglyceride)

[Aurelian]

In a transesterification reaction, no net water is produced. If you want to view the transesterification reaction in two steps, this may make things clearer; first hydrolyse the initial ester, using up some water, and then you have a condensation reaction with the fatty acids just released and the alcohol - this will produce some water as a byproduct.

Three waters produced, three used up. No net production of water. Hope that helps!

[mihir94]

Yeah just like Aurelian said, view it in two steps:

1.  Veg Oil + 3H₂O ------> Gylcerol + 3Fatty acid (hydrolysis)
2. 3Fatty acid + 3CH₃OH ------> Biodiesel + 3H₂O (condensation)

When you add both reactions (the fatty acids and water cancel), you get:

Veg Oil + 3CH₃OH ------>  Gylcerol + Biodiesel

Note that glycerol is the byproduct, but methonal could also be a product if it was used in excess.

[zibb3r]

THANKYOU!!!

[afeichuu]

wait I'm sorry, I'm still confused

where does the NaOH come in?

[jadams]

wait I'm sorry, I'm still confused

where does the NaOH come in?

Just as esterification reactions take place in an acidic environment, the reverse requires a basic environment. You don't have to understand why for VCE level.

[charmanderp]

Yeah just like Aurelian said, view it in two steps:

1.  Veg Oil + 3H₂O ------> Gylcerol + Fatty acid (hydrolysis)
2. Fatty acid + 3CH₃OH ------> Biodiesel + 3H₂O (condensation)

When you add both reactions (the fatty acids and water cancel), you get:

Veg Oil + 3CH₃OH ------>  Gylcerol + Biodiesel

Note that glycerol is the byproduct, but methonal could also be a product if it was used in excess.

You'd actually have 3 fatty acids, just a heads up.

In response to the above, NaOH is the catalyst for hydrolysis of the oil/fat to produce glycerol and three fatty acids.

[charmanderp]

wait I'm sorry, I'm still confused

where does the NaOH come in?

Just as esterification reactions take place in an acidic environment, the reverse requires a basic environment. You don't have to understand why for VCE level.

Hydrolysis doesn't have to occur in a basic environment, it's just more efficient.

[jadams]

wait I'm sorry, I'm still confused

where does the NaOH come in?

Just as esterification reactions take place in an acidic environment, the reverse requires a basic environment. You don't have to understand why for VCE level.

Hydrolysis doesn't have to occur in a basic environment, it's just more efficient.

Required probably has the wrong connotation haha...I meant that.

[charmanderp]

Probably just mention that it ideally needs an acidic or basic catalyst haha.

[mihir94]

Yeah just like Aurelian said, view it in two steps:

1.  Veg Oil + 3H₂O ------> Gylcerol + Fatty acid (hydrolysis)
2. Fatty acid + 3CH₃OH ------> Biodiesel + 3H₂O (condensation)

When you add both reactions (the fatty acids and water cancel), you get:

Veg Oil + 3CH₃OH ------>  Gylcerol + Biodiesel

Note that glycerol is the byproduct, but methonal could also be a product if it was used in excess.

You'd actually have 3 fatty acids, just a heads up.

In response to the above, NaOH is the catalyst for hydrolysis of the oil/fat to produce glycerol and three fatty acids.

Oh yeah, whoops. Thanks