A1.850 g mixture of srco3 and sro is heated. the srco3 decomposes to sro and co2. what was the mass percentage of srco3 in the mixture if the mass after heating is 1.445 g?

decomposition of SrCO3 to SrO and CO2 =change in mass

 moles of CO2 =(1.850 g - 1.445 g). 
Mass of CO2 in mixture: 1.850-1.445 = 0.405g
0.405g/44.01 g/mol CO2 = 0.0092 moles CO2.
ratio of CO2 to SrO in SrCO3 is 1:1
 mass ratio = 1.358/1.850 = 0.7341, 
or 73.41% SrCO3.
hope this helps

Neither model is able to show the reactivity of potassium.