Consider the crystallization of sulfanilamide from 95% ethyl alcohol. if impure sulfanilamide is dissolved in the minimum amount of 95% ethyl alcohol at 40°c rather than 78°c (the boiling point of ethyl alcohol), how would this affect the percent recovery of pure sulfanilamide? explain your answer.

Crystallization is purification technique in which the substance containing the impurities  is dissolved in the solvent near its boiling point. The solution is then allowed to cool slowly. This result in crystallization of the dissolved solid whereas the impurities remain the the solution form. As a result, the substance is purified.

It is important to dissolve the substance in a solvent near its boiling point. This allows maximum dissolution of the substance and hence higher percent recovery of the solid.

When we dissolve sulfanilamide in ethyl alcohol at 40 C instead of its boiling point, less amount of sulfanilamide gets dissolved in ethyl alcohol . This happens because as the temperature decreases, the solubility of the solid also decreases.

This would result in lower percent recovery of sulfanilamide

why is arctic sea ice important? arctic sea ice keeps the polar regions cool and moderate global climate. sea ice has a bright surface; 80 percent of the sunlight that strikes it is reflected back into space. as sea ice melts in the summer, it exposes the dark ocean surface.

pre-sliced bread is a relatively recent development in baking technology. previous to that, it was always sold in a bakery in daily-made contiguous loaves with no wrapping, and was moderately perishable, usually being used with a day or two (which is why every bakery had a discounted “day-old” bread table.) therefore, pre-sliced bread would grow stale quickly. the hard crust provided a protective layer, and once the exposed dry slice left from the previous cut was removed, the interior was still soft.

what keeps bread soft is the moisture retained in the crumb (the light spongy part that’s not crust). the reason the crust develops is the surface of the dough gets exposed to hot dry air during baking which browns the outer layer and seals it, preventing all the moisture from escaping the dough. longer exposure to air will also eventually cause your bread to lose flavor and become stale.

people were used to cutting slices as they needed them and storing bread in a specially-made wooden or metal breadbox or pail with a lid to preserve it longer, but the first automatically sliced commercial loaves were produced on july 6, 1928, in chillicothe, missouri, using a machine invented by otto rohwedder, an iowa-born, missouri-based jeweler.[1] pre-sliced bread would indeed dry out, were it not for another 20th century technology: the plastic bag. bread could now be pre-sliced, and if the enclosing bag remains sealed as much as possible, the bread will remain soft and fresh for longer than if sitting unwrapped on a shelf or enclosed in a bread box that is not air-tight. sealed packaging meant bread could also be sold on store shelves and eliminate frequent trips to a bakery.

sealing bread in a plastic bag had another effect: the moisture in the loaf will re-distribute into the crust and soften it, which is sometimes more pleasing in a sandwich - especially for children whose teeth might not yet be strong enough to tear through a hard crust. a homemade loaf of bread can be sealed in a bag overnight and the crust will become soft like store-bought sandwich bread.

these were novel changes in how bread was produced and sold, which led to the coining of the phrase “the greatest thing since sliced bread.”