Sciencemadness Discussion Board - Bicarbonate to carbonate; strange low yield?

Loading [MathJax]/jax/output/HTML-CSS/fonts/TeX/fontdata.js


	Not logged in [Login ]

FAQ

Member List

Today's Posts Forum Stats

Stats

Back to:

Sciencemadness Discussion Board » Fundamentals » Beginnings » Bicarbonate to carbonate; strange low yield?

Printable Version

Fulmen

International Hazard

Posts: 1748
Registered: 24-9-2005
Member Is Offline

Mood: Bored

posted on 1-3-2025 at 01:18

Bicarbonate to carbonate; strange low yield?

So I needed a bunch of sodium carbonate, and I calculated that it would be cheaper to start with sodium bicarbonate. According to Wikipedia 200°C should do nicely:

2 NaHCO3 => Na2CO3 + CO2 + H2O

I started with 550g, and my math tells me I should expect a yield of 405g. So why did I only get 355g? The bicarbonate was perfectly dry, and I can not find any data on any hydrates.

We're not banging rocks together here. We know how to put a man back together.

davidfetter

Harmless

Posts: 13
Registered: 8-9-2021
Member Is Offline

posted on 1-3-2025 at 08:45

Many things could account for what you see, to include:

"Dry" is harder to assess than you may think.
Scales are not always quite as accurate over their entire range as you may be assuming.
(unlikely) You got spots so much hotter that you may have NaOH.

Texium

Administrator

Posts: 4665
Registered: 11-1-2014
Location: Salt Lake City
Member Is Offline

Mood: Preparing to defend myself (academically)

posted on 1-3-2025 at 08:52

Or... you did your math wrong.

550 g bicarbonate / 84 g/mol = 6.55 mol

6.55 / 2 = 3.27 mol carbonate expected

3.27 mol * 105.99 g/mol = 347 g sodium carbonate

Come check out the Official Sciencemadness Wiki
They're not really active right now, but here's my YouTube channel and my blog.

Texium

Administrator

Thread Moved
1-3-2025 at 08:52

bnull

National Hazard

Posts: 596
Registered: 15-1-2024
Location: Home
Member Is Offline

Mood: Sneezing like there's no tomorrow. Stupid cat allergy.

posted on 1-3-2025 at 08:53

Quote: Originally posted by Fulmen

I started with 550g, and my math tells me I should expect a yield of 405g.

405 g? Let's see.

2 moles of NaHCO₃ = 2*84=168 g
1 mole of Na₂CO₃ = 106 g
550 g/168 g=3.27
3.27*106 g=347 g

Quote:

So why did I only get 355g?

Because you didn't heat it for long enough.

Edit: Try this: Balance Chemical Equation.

[Edited on 1-3-2025 by bnull]

Quod scripsi, scripsi.

B. N. Ull

We have a lot of fun stuff in the Library.

Read The ScienceMadness Guidelines. They exist for a reason.

Fulmen

International Hazard

Posts: 1748
Registered: 24-9-2005
Member Is Offline

Mood: Bored

posted on 1-3-2025 at 09:04

Quote: Originally posted by Texium

Or... you did your math wrong.

Nope, apparently I did it wrong 3 times! Jeeez, I'm getting soft.
Edit: I found it. My bicarbonate was carbon neutral with a molar weight of 72 :-D

@ bnull: We're within the limits of kitchen chemistry and scales here. But I did notice a bit of low solubility material in it so you're probably right. Not that it matters, I'm just making sodium nitrate from calcium nitrate. The bicarbonate should do the same job, but it's low solubility and CO2 generation would make for a messy reaction.

[Edited on 1-3-25 by Fulmen]