Given :
2 Mg + O₂ → 2 MgO
To Find :
How many moles of magnesium oxide are formed if you burn a 2.3 mol sample of magnesium ribbon in the air.
Solution :
From given balanced chemical reaction we can see that 2 mole of Magnesium reacts with 1 mole of O₂ to produce 2 mole of MgO.
Since, there is abundance of oxygen in air.
Therefore, 2.3 moles of magnesium will produced 2.3 moles of magnesium oxide.
N2 + 3 H2 >> 2 NH3
moles NH3 = 11.50 g /17.0307 g/mol=0.6753
the ratio between H2 and NH3 is 3 : 2
moles H2 needed = 0.6753 x 3/2 =1.013
mass H2 = 1.013 mol x 2.106 g/mol=2.042 g
Answer:
Weigh 4.5 grams of sodium hydroxide and add it to the dry volumetric flask of 450 mL followed by small amount of water to dissolve all the NaOH .After this add the water upto tye mark of 450 mL.
Explanation:
Molarity of the solution is the moles of compound in 1 Liter solutions.

Mass of NaOH = x
Molar mass of NaOH = 40 g/mol
Volume of the NaOH solution = 450 mL =- 0.450 L ( 1 ml = 0.450 L)
Molarity of the solution of NaOH = 0.250 M


Solving for x:
x = 4.5 g
Weigh 4.5 grams of sodium hydroxide and add it to the dry volumetric flask of 450 mL followed by small amount of water to dissolve all the NaOH .After this add the water upto tye mark of 450 mL.
Using the significant figure it would be 27.3