Questions about mixtures and compounds?

Is this a mixture or a compound? If you have two powdery substances A and B, and when they are both added to seperate beakers of water they dissolve. Then when you pour them into the same beaker together the water turns yellow and white stuff appears a the top and starts to float to the bottom, is it a mixture or a compound? This is not homework, just something we did in cl that I didn't get.