Does covering a pot of water when heating it on the stove make it boil faster?
The various answers do largely address relevant factors that determine the speed of boiling water in a pan. For a pan lid that floats and rattles about on the boiling water, the elevation of pressure will be insignificant in terms of raising the boiling point of water.The single most important factor, hardly touched upon among several of the answers, is the effect of the lid on condensing the hot, saturated vapour and draining it back into the water being heated. The amount of latent heat in water vapour is extremely large (540 cal/gm) and, if the latter is condensed back into the water, would make a significant difference to the time taken for the water to reach bp.Indeed , it is common experience that when the lid is hopping about on the top edge of the pan due to steam pressure at the boiling temperature, it is necessary to reduce the heat input substantially in order to prevent over-boiling in contrast with maintaining boiling conditions for an open pan. The reason? - condensation of steam back into the water. The heat-recovery effect of vapour condensation at lower temperatures reduces the time required to boil the water over that without a lid.The principle of recovering latent heat from the products of combustion is exploited in gas-fired condensation boilers.
Why does milk boil faster than water?
Water has a heat capacity of 4.184 J/g. So that means that it takes 4.184 Joules to heat 1 gram of water by 1 degree Celsius. Milk has a heat capacity of 3.93 J/g meaning it takes a little less energy to heat milk than water. Milk is mostly water so that 6% difference between the two is all the other stuff that comes in milk, such as protein, calcium, etc. Few, common, things have a heat capacity higher than water, so by adding almost anything to pure water it will mean that it will boil ever so slightly faster.
What happens when carbon dioxide is passed through lime water?
Lime water is basically an aqueous solution of Calcium Hydroxide , formula, [math]\text{Ca(OH)}_2 [/math].So this solution is alkaline, and Carbon Dioxide is acidic oxide. So when Carbon dioxide ([math]\text{CO}_2[/math] ) is passed through lime water, an Acid-Base reaction takes place producing salt and water.The reaction is written as,[math]\text{Ca(OH)}_2 + \text{CO}_2 \rightarrow \text{CaCO}_3+\text{H}_2\text{O}[/math]Calcium Carbonate ( [math]\text{CaCO}_3 [/math]) is insoluble in water, thus forming white precipitate, making the solution appear milky.This also serves as the classic test for carbon dioxide.Now, if through the milky solution, more Carbon dioxide is passed, the milkiness disappears.The reaction is,[math]\text{CaCO}_3 + \text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{Ca(HCO}_3\text{)}_2[/math]This Calcium Bicarbonate is soluble in water. Thus milkiness disappears on passing excess Carbon Dioxide.
Is is true that hot tea in a plastic cup can cause cancer?
I know from my Indian friends that this topic has been rather hotly debated in India lately.The answer is we do not know definitively. However, there is good cause for concern. One of the most common chemicals in plastic cups is styrene. Styrene was added to the the USA Dept. of Health Human Services list of known carcinogens in 2011. This move was opposed by plastic manufacturers and would not have happened without quite clear proof. So, we may reasonably sure that styrene causes cancer.That leaves us with two questions.Does hot tea result in the migration of styrene from plastics into the tea itself? Fortunately, this one has been researched. An article published in the Journal Toxicology Mechanisms and Methods in 2009 established that styrene from general purpose plastics (GPP) does indeed migrate to hot beverages and that the migration showed a direct correlation to two factors, temperature and fat content. Bad news for those who like a spot of milk with your tea. You just doubled your styrene exposure.This leads to the 2nd question. Is the styrene exposure sufficient to be considered a cancer risk? The answer to this also seems to be yes. In the same study noted above, the researchers found that the level of styrene migration exceeded the Maximum Contaminant Level Goal set by the USA Environmental Protection Agency.So in summary, general purpose plastics do contain styrene, a known carcinogen. Hot tea has been tested and does absorb toxic level of styrene. There is no specific research that I am aware of linking drinking tea in plastic directly to cancer but the indirect linkages seem to me strong enough that one would be well advised to avoid hot tea in plastic containers.As an aside, I agree with the other respondents who cited BPA as a concern. BPA is not a carcinogen, but, for young women in particular, it does present a serious health risk and, yes, BPA is released from plastics by hot beverages.Hope that helps.
How will you show experimentally that metals are good conductors of heat?
Hari om,you are askinga question as to : “ How will you show experimentally that metals are good conductors of heat?”. Hari om.ANSWER :Technique -1 :Take half a liter of water and boil it over the stove. Stir the water with a metal spoon / wooden spool for 30 seconds. The metal spoon would get so hot that you can't hold it, while the wooden spool does not get heated at all. This shows that metal is a good conductor of heat, compared to wood.Technique -2 :Take a cup of milk (100 ml ) in a metal vessel and a mud vessel, and start heating them simultaneously on two different stoves with the same flame size.The milk in the metallic vessel will boil and overflow fast.This shows that the metal container is a good heat conductor, compared to the mud container.Technique -3 :Boil dal in a cooker. After steam goes out, knead the hot dal with a metal spatula. You will feel the hotness of the spatula as it is a good conductor of heat.Now, do the same thing, with a wooden batten. You will not feel the heat at all. This shows that the wood does not conduct heat, while the metal conducts heat very well.The above 3 (techniques ) demonstrate that the metal is a good conductor of heat compared to the wood materialHari om. Hari om.
Why don't we use a metal spoon in cooking?
Metal spoons are fine for use in un-coated cookware like stainless steel, cast iron, aluminum, or carbon steel.On the other hand, you should never use metal utensils with coated non-stick cookware. It will scratch the coating, which will ruin the nonstick properties of the pan. Also, you don’t want the coating to end up in your food because most non-stick coatings are carcinogenic.When cooking in non-stick pans, you should always use wood, heat-resistant silicone, or plastic. It will make your pans last longer, and reduce you chance of developing cancer.