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Author Topic: A few basic questions  (Read 3284 times)

Crazy117

• First timers
• Posts: 9
A few basic questions
« on: 29/11/2005 21:02:22 »
What would be the mass and volume ratio of potassium to carbon after potassium carbonate has undergone a decomposition reaction?
Is the size of the atoms a factor?
Would the amount of atoms of a certain element in a single molocule of potassium change the ratio?
Does potassium rapidly subliminate?
How do I calculate buoyancy?
What is the density of potassium?

Simmer

• Sr. Member
• Posts: 229
Re: A few basic questions
« Reply #1 on: 30/11/2005 21:03:04 »
quote:
]Originally posted by Crazy117

Like most basic questions there are a number of different interpretations of what they mean, all difficult to answer!

My best shot at it follows, however:

quote:
What would be the mass and volume ratio of potassium to carbon after potassium carbonate has undergone a decomposition reaction?

If you mean thermal decomposition, the products, according to the literature, would be a mixture of potassium oxide (K2O), carbon monoxide (CO) and carbon dioxide (CO2).

As the carbon would be in the form of a gas, each mole at STP would be about 22 L, whereas the potassium oxide is a solid with a density of 2.32 g/cm^3 so one mole would be about 41 cm^3 (volume ratio of about 536 of carbon to 1 of potassium)

The mass ratio would be unchanged, of course.  Potassium masses about 39.1 amu, two of them in potassium carbonate so 78.2 g/mole while carbon masses about 12.0 amu, only one in potassium carbonate, so 12.0 g/mole. (Mass ratio = 0.15 of carbon to 1 of potassium)

quote:
Is the size of the atoms a factor?

Not in this case, the critical factor in the volume thing was whether the product was a gas or a solid.  In general, among the elements, most of the gases are at the top (lighter) end of the table so you could argue that there is some correlation.

quote:
Would the amount of atoms of a certain element in a single molocule of potassium change the ratio?

Not quite sure what you mean here - potassium isn't a molecule of course - do you mean the molecule containing the potassium?

quote:
Does potassium rapidly subliminate?

No.  Strictly speaking it doesn't sublime, it melts before it boils, but in any case it has a high boiling point so I would expect that its vapour pressure (and therefore mass flux) would be low.  In air it usually oxidises very rapidly anyway.

quote:
How do I calculate buoyancy?

Buoyant force is equal to the mass of fluid displaced.  So a ten centimetre cube immersed in water will displace 1 kg of fluid and that will be the buoyant force it experiences.  If the cube weighs less than a kilogram it will float.

A cheaper way to tell whether something will float in water or not is to look at the density - the density of water is usually taken to be about 1 g/cm^3 (although that varies with stuff like temperature and salinity) so anything with a density of less than that is likely to float.

quote:
What is the density of potassium?

At last, an easy one! 0.89 g/cm^3 at room temperature.  Technically it would float in water but it reacts so violently with water that it would make a very poor buoyancy aid!
« Last Edit: 30/11/2005 22:55:20 by Simmer »

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Re: A few basic questions
« Reply #1 on: 30/11/2005 21:03:04 »

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