This is a fun KS3 chemistry tarsia for acids and alkalis. There are 16 triangles with 18 pairs of questions and answers that make a parallelogram. I suggest that the A4 tarsia is printed on card and then the outline is cut out. Students can then quickly cut out the individual triangles. Included are the following topics: indicator, pH meter, pH of different substances, formula of HCl and water. The software is free to download but there is not currently a version for Mac computers.