Answer :
The student's question involves calculating the phases and compositions of a Pb-Sn alloy at 195 oC. Without the specific phase diagram, exact compositions cannot be given, but the alloy would consist of solid phases of lead and a tin-rich alloy since this temperature is below the melting points of both pure Pb and pure Sn.
The student is asking about the phases and chemical compositions of an alloy at 195 oC that originally consisted of 45% Sn (tin) and 55% Pb (lead) by mass. This question relates to the study of phase diagrams and eutectic points for alloys.
At 195 oC, according to the Pb-Sn phase diagram, the alloy would have passed the eutectic temperature and would be in a solid state, consisting of a mixture of two solid phases: solid lead and solid tin-rich phase. The exact compositions of each phase would depend on the specific point on the phase diagram at this temperature. To calculate the compositions, one would look at the isothermal line at 195 oC and determine where this intersects with phase boundaries.
Unfortunately, without the Pb-Sn phase diagram, it's not possible to provide exact compositions. However, in general, one would use the lever rule to determine the proportion of each phase. Given that the melting point of pure Pb is 327 oC and the melting point of pure Sn is 232 oC, and this alloy is cooled below both melting points, both metals will be in solid state, forming a mixture of crystal structures.
