We will use the expression for freezing point depression ∆Tf
∆Tf = i Kf m
Since we know that the freezing point of water is 0 degree Celsius, temperature change ∆Tf is
∆Tf = 0C - (-3°C) = 3°C
and the van't Hoff Factor i is approximately equal to 2 since one molecule of KCl in aqueous solution will produce one K+ ion and one Cl- ion:
KCl → K+ + Cl-
Therefore, the molality m of the solution can be calculated as
3 = 2 * 1.86 * m
m = 3 / (2 * 1.86)
m = 0.80 molal
Counting atoms in a compound can be done by taking one element at a time and multiplying the subscript of the element and the number of molecules of the compounds. For example, H2O, there are two atoms of H adn 1 atom of oxygen.
The density of the gold is 19.3 grams/cc so each cc weighs 19.3grams. Now we can obtain the volume of gold from the given dimensions ie 4.72x8.21x3.98= 154.23 cc. So for the answer, just multiply the volume or 154.23 x 19.3= 2976.6 grams is the answer.
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When ammonium chloride NH4Cl is added to water and stirred, it dissolves spontaneously (this is the basis for ΔG) for and the resulting solution feels cold (endothermic, the basis for ΔH). Without doing any calculations, we can easily deduce the signs of ΔG, ΔH, and ΔS for this process based on the observations.
ΔG < 0 (it is spontaneous)
ΔH < 0 (because the process is endothermic - it absorbs energy)
ΔS > 0 (entropy increases because of the dissolution of NH4Cl in water
