Question

3 2. According to the US Mint, a standard gold bar weighs in at 27.43 lb and has a length of 7 5 inches, a width of 3 inches, and a height of 17 inches. Considering that gold is known to crystallize in a face-centered cubic crystal structure, calculate the atomic radius of a gold atom. 3. How much energy, in kilojoules, must applied to a 455 g block of iron at 25 °C to convert it to aliquid at 2000 °C? (NOTE: You will need to search the internet for physical constants) 4. A solution is formed by added 12.50 g of an unknown substance to 250.0 g of water. This solution was determined to have a boiling point of 105.50 °C. a. Assuming that the unknown substance is a non-electrolyte, what is its molar mass? b. Assuming that the unknown substance is not volatile, calculate the vapor pressure of the solution.

Answer 1

Answer 3:

As per the heat eqaution

Q = mc ΔT

m = mass of substance = 455 g

Q = heat required to reach the particular temperatrue

C= specific heat capcity of iron = 0.444 J/g^oC

ΔT = (Final Temperature -intial temperature) = (200-25 ) =175 ^oC

Q = 455 * 0.444 * 175

Q = 35353.5 J

Q = 35.35 Kj

So total heat required would be 35.35 KJ

Answer 4:

Part (i)

As compound is unionized so i value will be 1 in the below equaiton :

ΔT = K_b * m *i

Kb of water is 0.51c/m

ΔT = Boiling point of solution - boiling point of water

= 105.5 -100

= 5.5 ^oC

If we calculate the m for the same:

m = 5.5/0.51

= 10.784 mol/kg of water

As we have used the 250 g of water so mole of substance is = 10.784*0.25 = 2.696 moles.

As 12.5 g contains the 2.696 moles so 1 moles contains 4.63 g

so molar mass is 4.63 g/mole