1) Write the balaced chemical equation:
H2 + 2O2 → 2H2O
2) Infere the molar ratios:
1 mol H2 : 2 mol of water
3) Make the calculus as the direct proportion relation:
[2 mol H2O] / [1 mol H2] * 7 mol H2 = 14 mol H2
As you see you produce the double number of moles of H2O than number of moles of H2 used.
Answer: 14 moles
After 100years, sample is 250g
After 200 years, sample is 125g
After 300years, sample is 62.5 g
There will be needed 982.35 mL of solution to obtain 16.1 grams of the salt.There will be needed mL of
Why?
In order to calculate how many milliliters are needed to obtain 16.1 grams of the salt given its concentration, we first need to find its chemical formula which is the following:

Now that we know the chemical formula of the substance, we need to find its molecular mass. We can do it by the following way:

We have that the molecular mass of the substance will be:

Therefore, knowing the molecular mass of the substance, we need to calculate how many mols represents 16.1 grams of the same substance, we can do it by the following way:


Finally, if we need to calculate how many milliliters are needed, we need to use the following formula:


Now, substituting and calculating, we have:

Henc, there will be needed 982.35 mL of solution to obtain 16.1 grams of the salt.
Have a nice day!