A30.7 g sample of strontium nitrate, sr(no3)2•nh2o, is heated to a constant mass of 22.9 g. calculate the hydration number.

The difference of the sample mass and the heated sample mass is the amount of water which evaporated by heating process, then we can calculate:  

mass of H₂O = 30.7 -  22.9 = 7.8 g

then calculate the number of moles:  

number of moles of H₂O =  mass / molecular mass

number of moles of H₂O = 7.8 / 18 = 0.43 moles

So the hydration number is 0.43.

Sr(NO₃)₂ • 0.43 H₂O

a

explanation:

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.