sentences:  The resulting solution is then filtered to remove any undissolved acetylsalicylic acid and is mixed with a solution containing Cu2+ cations (copper(II) sulfate is suitable), precipitating bright blue crystals of copper aspirinate immediately.The crystals can then be filtered from solution, washed, and dried.An excess of acetylsalicylic acid is used in the first step, because it eliminates the possibility of unreacted carbonate anions precipitating the copper in this step.