Lead crystallizes in a face-centered cubic structure with a density of 11.34 g/cm3. Polonium crystallizes in a simple cubic structure with a density of 9.3 g/cm3. Explain why lead has a greater density than polonium even though polonium atoms are heavier, and smaller than lead atoms.

Explanation:

In a face-centered cubic structure, each unit cell has 4 atoms. Each of the 8 corner atoms contribute 1/8 part to the unit cell and each of the 6 atoms at face-centres contribute 1/2 part to the unit cell. So, each unit cell has net 4 atoms.

In a simple cubic structure, there are 8 atoms, one at each corner. So, each one of them contribute 1/8 part to the unit cell. So, the unit cell has only 1 atom effectively.

Hence, each cell units of lead has 4 times as atoms as in the unit cells of polonium.

Due to this, density of lead is higher despite the fact that it's atomic mass is smaller and the size is bigger than that of a polonium atom.

state the principle of separating two immiscible liquids by separating funnel. describe an activity with diagram to separate a mixture of water and kerosene oil. answer: immiscible layers separate out in layers depending on their densities in separating funne

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.”