Mv^2 = const
<span>m ~ 1/v^2 </span>
<span>(4.5/10.1)^2 = 0.198 </span>
<span>20.2 * 0.198 = 4.0 g/mol (Helium)</span>
valence of magnesium is 2
and valence of sulfate-ion is 2 too
answer: MgSO4•7H2O
The mass of any substance will remain the same regardless of its state of matter. Using water as an example, its volume increases when it is boiled to a gas or when it is frozen from a liquid state to the solid state ice. The volume and temperature will change as it moves through the states of matter, however the amount of individual molecules of oxygen and hydrogen that form water will remain the same and this constitute mass.
Answer : The mass of oxygen formed must be 3.8 grams.
Explanation :
Law of conservation of mass : It states that mass can neither be created nor be destroyed but it can only be transformed from one form to another form.
This also means that total mass on the reactant side must be equal to the total mass on the product side.
The balanced chemical reaction will be,
According to the law of conservation of mass,
Total mass of reactant side = Total mass of product side
Total mass of 
= Total mass of 
As we are given :
The mass of 
= 25.3 grams
The mass of 
= 23.4 grams
So,
Therefore, the mass of oxygen formed must be 3.8 grams.
Atoms of sulfur = 9.60⋅g32.06⋅g⋅mol−1×6.022×1023⋅mol−1 . Because the units all cancel out, the answer is clearly a number, ≅2×1023 as required.
