1. The PDF entry for calcite was used to identify d spacings in the list (ancient plaster figure) which corresponded to calcite. The order of the d spacings in terms of intensity in the PDF entry were compared with the order of the d spacings identified for calcite in the list (ancient plaster figure). The orders were found to match, thus suggesting that the other compounds present did not have d spacings with strong intensities at the same d spacings as calcite.


Comment: This is essentially correct, including your point about getting the correct order of intensities. On this point however there are two lines (2.284 and 1.510) which appear to be anomalous from point of view of both intensity and peak width. The reasons for this however unfold (see model answer).
3.5 Marks

2. The d spacings for calcite were removed from the list (ancient plaster figure) and the updated list had the three d spacings with the strongest intensities identified. These three d spacings were used with pages 13 to 16 of the Hanawalt search index to identify that silicon dioxide has the same d spacings with the same order of intensities. The PDF data card (5-490) for silicon dioxide was used to identify all of the other d spacings, which corresponded to silicon dioxide in the updated list.


Comment: This is the correct solution though more detail could be given (see for example the model answer).
4 Marks

3. The remaining list (ancient plastic figure) with the d spacings for both silicon dioxide and calcite removed had the next three d spacings with the strongest intensities identified. The three d spacings were used alongwith the Hanawalt search index to identify magnesium carbonate as having the same three d spacings with the same order of intensities. The PDF datacard for magnesium carbonate (8-479) was used to identify the d spacings in the remaining list, which corresponded to magnesium carbonate.

   
   Comment: similar to the previous case.
   4 Marks

4. The solution appears to be correct, however, the solution would not have been so straightforward if there had been more silicon dioxide present. Silicon dioxide and calcium carbonate (calcite) have d spacings at 2.282 and 2.285 angstroms respectively. If more silicon dioxide had been present, then this would have given rise to a d spacing with an increased intensity and thus an incorrect order of d spacings would have been used to search the Hanwalt search index and thus an incorrect result would have been obtained.

   
   Comment: Your point about the concentration of silicon dioxide is interesting though I am sure normal searches would still have survived this complication.
   3.5 Marks

General Comment: Overall you have produced a correct solution though much more detail would have helped; e.g. a summary table with all the lines attributed to their respective phase. You need to provide more explanation as to how you arrived at the correct answers.