4. why is it important to use a large excess of sodium borohydride when doing a reduction in aqueous ethanol? (hint: consider what reaction might occur between water and sodium borohydride.)

Hey there!:

Aqueous ethanol contains water , sodium borohydride will react with water and decompose to give hydrogen gas :

NHB4 + 2 H2O => NaBO2 + 4 H2

thus a large excess of borohydride should be used used to take into account losses from the reaction with water , so that there is sufficient sodium borohydride left for the reduction of the chemical compound os interest .

Hope this helps!

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%

while cooking a piece of 1/2 pound beef steak, a cast iron pan (2.4kg in weight) was heated 260 celsius.