A scientist is attempting to check the relative atomic masses on the periodic table. He works with three different compounds that contain only C and another compound. These are diatomic compounds with a formula of CX. He finds the following information. If he assumes the weight of C is 12 what is the weight of the other element (X1, X2, X3) and what is the identity of each unknown element? Compound 1 Compound 2 Compound 3
Wt C Wt X 4.2 4.9 3.5 4.67 1.3 3.47

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.

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.