Leaderboard

Soap is an artificial compound called sodium stearate. Soap nuts are the fruits of the soap nut tree which contain a substance that looks a bit like liquid hand soap but is 100% natural and called saponin. Saponin is a natural detergent (detergents are a general term for cleaning compounds that work with water). I thought we had answered that rather fully. Sodium carbonate has several different crystalline forms, which are rather temperature and moisture dependent. The temperature of This is exactly what my diagram shows. Below 30oC, the decahydrate is the stable form and its solubility drops rapidly with temperature, hence your crystals. Because solution of the decahydrate required intake of heat, dissolving lowers the solution temperature further promoting crystallisation. Warming these a bit drives off some of the water of crystallisation and the crystals revert to another form, the heptahydrate as the whitish powder coating on the outer parts since that is where the water leaves the crystals. You will not get the anhydride unless you heat very hard and your starting point (the bicarbonate) will probably reduce to a mixture of carbonate and bicarbonate when you first put it in the oven. This is called sodium sesquicarbonate.

So was I. Essentially, if you can go 50 ly in 1 million years under constant acceleration, then it would take ~450,000 yrs to go 10 ly starting from "rest". Waiting until you get warning of an imminent supernova is likely not an option. But that doesn't mean we couldn't try and keep our distance from supernova candidates. We know that only stars above a certain mass supernova. So maybe the strategy would be "Why wait for trouble? Let's just keep our distance from any stars that could even possibly supernova." Pluto shouldn't be left behind. If we go by the 50 ly in 1,000,000 year at constant acceleration scenario, then the acceleration needed is 4.27e-10m/s2, While the centripetal acceleration for Pluto is 3.8e-6 m/s2, several magnitudes larger.

Incorrect. Typo. OK. Incorrect.

Could the connection not be named after Planck instead of after Strange? The difference between pi and phi is exactly h .

Kinda depends where you are. There is a definite shortage of Chemistry tutors in my region (SW England) and those there are charging silly money as a result. I was talking about this last night to a friend in Oxford who place science tutors and he said there is no shortage in Oxford and no price premium there. A word about exams. It is difficult to achieve high marks in the essay type questions, and it takes longer to answer a question as compared to the calculation questions. So get your brother lots of (calculation) practice questions - there are plenty of books of these available including cheap second hand ones. On aspect of doing calculations is that you need to know the theory (which you say he does) to attempt them properly, so doing calculations make one look up missing points of theory. Also get him to join up here at SF and post questions. We have several high school chemistry students who find good quality help here.

I don't quite see how ? The Wiki article I linked to says quite clearly that the bicarbonate is manufactured first as a precursor of the carbonate. Since sodium carbonate is quite soluble, but calcium carbonate is not, you are not likely to find much sodium carbonate free in Nature. So it has to be prepared from a soium salt (commonly the chloride). The original process (LeBlanc) was by way of sulphuric acid, the modern(?) process (Fresnel-Solway) is via ammonia. There is also an alectrolytic process, based on the Nelson Cell which makes it directly from carbon dioxide and sodium hydroxide. But then you have to get the hydroxide from somewhere. Here is some more (numeric) information which confirms why you are having to heat your decahydrate crystals. Heats of solution are as follows Anhydrous salt Na2CO3 + Aq = Na2CO3 (aq) ΔH = -5640 calories Monohydrate Na2CO3.H2O + Aq = Na2CO3 (aq) ΔH = -2250 calories Decahydrate Na2CO3.10H2O + Aq = Na2CO3 (aq) ΔH = +16160 calories The negative sign of the first two indicate that heat is evolved on solution of the salt, making the reaction thermodynamically favourable. But the decahydrate absorbs heat (positive sign) to dissolve, which is why you have to heat it.

This page might interest you. Note hte abrupt solubility change in the temperature region you mention.

You got it.

And to shed heat, it requires the surroundings be at a lower temperature.

Yes, that is generally acknowledged to be the best way to overthrow centuries of increasingly precise measurements.

It can be shown that as x approaches 0 from the right side, 1/x will approach 1/0 and apporach positive infinity. And it can be shown that as -x approaches 0 from the left side, -1/x will approach negative infinity and apporach -1/0, which is equal to (-1/-1)*-1/0 equals 1/0, since 0 is neither positive or negative. Showing that 1/0 is not even a number, and does not represent a distinct point on the real number line.