However, this surface soon tarnishes because of reaction with oxygen and moisture from the air. If potassium is burned in air, the result is mainly formation of orange potassium superoxide, KO 2. Potassium metal reacts very rapidly with water to form a colourless solution of potassium hydroxide KOH and hydrogen gas H 2. The resulting solution is basic because of the dissolved hydroxide. The reaction is exothermic. It is best to hold the cylinder nearly horizontal, to enable the air to mix with the hydrogen.
If the cylinder is almost full of hydrogen it burns quietly. If less sodium is used, then on lifting the cylinder out of the water, air goes in, and on lighting the gas one gets a very satisfying "bark" not an explosion , along with a characteristically orange flame.
If potassium is used, the teacher has to be that much more skillful! On igniting the hydrogen, one gets a light purple flame. I devised this demonstration some years ago but recently saw that a French chemistry teacher, M. The first time I do the demonstration, I prefer not to add phenolphthalein, so that there will be more scope for inquiry. When I do add it, I add it to all the water before placing it in the cylinder, so that on reaction the colour change is associated with the reaction in this video this is not the case.
The experiment can also be carried out quantitatively by removing the oil from the piece of sodium with petrol ether. The dry sodium can be rapidly weighed, then re-immersed in oil. The volume of hydrogen released is measured. Three pieces of Na were used with a total mass 0. Volume of hydrogen released — using a mL cylinder as I wanted greater precision — was mL. This way I obviated the need to measure temperature and pressure, and to take into account the vapour pressure of water.
I just had to unscrew the burner head above the tap and attach a flexible tube to the outlet and bubble gas into the same inverted measuring cylinder. Mass of gas giving mL was measured as 0. Hence mL corresponds to 0. In this reaction, increase in temperature is predicted and therefore affects the volume of the gas collected. This temperature effect was considered negligible. This is an additional opportunity for inquiry.
Have students predict the temperature increase and determine the effect on the volume of hydrogen. However, it does not have a radio toxicity class, because of its natural origin.
There is a total of twelve instable potassium isotopes. Potassium is a dietary requirement for us, and we take up about g per day at a requirement of The total potassium amount in the human body lies somewhere between and g and mainly depends upon muscle mass. The muscles contain most potassium after red blood cells and brain tissue.
Whereas its opponent sodium is present in intracellular fluids, potassium is mainly present within cells. It preserves osmotic pressure. The relation of potassium in cells to potassium in plasma is , and is regulated by means of sodium-potassium pumps. Vital functions of potassium include its role in nerve stimulus, muscle contractions, blood pressure regulation and protein dissolution.
It protects the heart and arteries, and may even prevent cardiovascular disease. The relation of sodium to potassium used to be , and is now about , which mainly prevents high sodium uptake. Potassium shortages are relatively rare, but may lead to depression, muscle weakness, heart rhythm disorder and confusion.
Potassium loss may be a consequence of chronic diarrhoea or kidney disease, because the physical potassium balance is regulated by the kidneys. When kidneys operate insufficiently, potassium intake must be limited to prevent greater losses.
Skin contact with potassium metals results in caustic potash corrosion. This is more hazardous than acid corrosion, because it continues unlimitedly. Caustic potash drops are very damaging to the eyes.
The intake of a number of potassium compounds may be particularly harmful. At high doses potassium chloride interferes with nerve impulses, which interrupts with virtually all bodily functions and mainly affects heart functioning. Potassium alum may cause stomach complaints and nausea at concentrations as low as 2 g, and may be corrosive and even lethal in higher concentrations.
Potassium carbonate is lethal to adults at doses above 15 g. The same goes for potassium tartrate at 1 g, and for potassium cyanide at only 50 mg. Potassium dichromate is lethal at between 6 and 8 g, and 30 g of potassium nitrate causes severe intoxication, which may result in death. Potassium permanganate is applied in bleaches and disinfection, and is lethal at between 5 and 8 g. Which water purification technologies can be applied to remove potassium from water?
Potassium may be removed from water by means of reverse osmosis. Potassium is applied in water purification. For example, potassium permanganate is applicable for oxidation of waterborne compounds, such as for iron or manganese removal, and disinfection. This is however not generally recommended.
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