Magnesium reacts with water in the equation, Mg+2H²O-->Mg(OH)²+H². You have 8.1 g of magnesium available. This means you will need ___ g of water to use all the magnesium.
This seems sorta simple, but how can i set it up?
These are stoichiometry problems. They can be solved with a 4 step procedure. Remember this--it will solve many a problem for you.
Step 1. Write the balanced equation.
You have done that.
Mg + 2H2O ==> Mg(OH)2 + H2
Step 2. Convert what you have to mols remembering (for mass) that mols = grams/molar mass.
mols Mg = 8.1/24.3 = 0.333 mols.
Step 3. Using the coefficients in the balanced chemical equation, convert mols of what we have (in this case mols Mg) to mols of what we want (in this case H2O).
mols H2O = mols Mg x (2 mols H2O/1 mol Mg) = 0.333 x 2/1 = 0.667 mols H2O. [Note that the 2 mols H2O/1 mol Mg come directly from the equation.
Step 4. Now convert what we have from step 3 to grams.
grams = mols x molar mass
g H2O = mols H2O x molar mass H2O.
g H2O = 0.667 x 18 = ??
Check my work. Check my numbers. I estimated the molar masses so you will need to redo them and recalculate everything.
ok im working on it- slowly..
Briana--I'm calling it a night. If you have some question about the procedure, post a new question and someone will take care of it for you. I'm not the only one answering chemistry questions.
so- the answer would be 12.006? if that's right then yay! i think im understanding these...
Thanks for all your help!
See above. Yes, your answer is correct.
your answer is correct. Actually, two significant figures is the limit (since 8.1 has two s.f.) so 12 would be the correct answer for s.f. purists.
To solve this problem, you can follow a four-step procedure:
Step 1: Write the balanced equation.
The balanced equation for the reaction is: Mg + 2H2O → Mg(OH)2 + H2.
Step 2: Convert the given amount to moles.
Given the mass of magnesium is 8.1 g.
To convert this to moles, divide the mass by the molar mass of magnesium.
The molar mass of magnesium is 24.3 g/mol.
So, moles of magnesium = 8.1 g / 24.3 g/mol = 0.333 mol.
Step 3: Use the coefficients in the balanced equation to convert moles of magnesium to moles of water.
From the balanced equation, the coefficient of magnesium is 1, and the coefficient of water is 2.
So, moles of water = moles of magnesium × (2 moles of water / 1 mole of magnesium)
= 0.333 mol × (2 mol H2O / 1 mol Mg) = 0.667 mol of water.
Step 4: Convert moles of water to grams.
To convert moles to grams, multiply the moles of water by the molar mass of water.
The molar mass of water is 18 g/mol.
So, grams of water = 0.667 mol × 18 g/mol = 12 g.
Therefore, you would need 12 grams of water to use all the 8.1 grams of magnesium.