CREATE TABLE table_25105 ("State  ( class ) " TEXT, "Vacator" TEXT, "Reason for change" TEXT, "Successor" TEXT, "Date of successors formal installation" TEXT)

Name the state class for iowa admitted to the union december 28, 1846
SELECT "State (class)" FROM table_25105 WHERE "Reason for change" = 'Iowa admitted to the Union December 28, 1846'
SELECT "State (class)" FROM "table_25105" WHERE "Reason for change" = 'Iowa admitted to the Union December 28, 1846'