What is the number of moles in 0.025 g (NH4)2Cr2O7? A) 1.5 x 1022
B) 4.2 x 10-26
C) 6.3
D) 1.0 x 10-4
E) 1.0 x 104

When the chemicals iron sulfide (fes) and hydrochloric acid (hcl) are combined, bubbles appear from the mixture. 1. does the appearance of bubbles indicate a physical or chemical change? 2. why do the bubbles indicate this change? 3. what property is this?