Two methods used by students to measure the rate of a reaction are the 'disappearing cross' method and the 'loss of mass' method. • For the 'disappearing cross' method, the student measures the time taken for the reaction mixture to go cloudy. • For the 'loss of mass' method, the student measures the loss of mass over a known time interval. The rates of two reactions are investigated. reaction 1 Warm aqueous silver nitrate is added to chlorobutane dissolved in ethanol. Two products are formed. One is an organic compound which is soluble in ethanol and the other is silver chloride which is insoluble in ethanol. reaction 2 Pieces of solid calcium carbonate are added to dilute hydrochloric acid. Which method should be used for each reaction?