Question

Pure magnesium metal is often found as ribbons and can easily burn in the presence of oxygen. When 4.20 g of magnesium ribbon burns with 6.75 g of oxygen, a bright, white light and a white, powdery product are formed.

Enter the balanced chemical equation for this reaction. Be sure to include all physical states.

equation:_________________________

What is the limiting reactant? oxygen OR magnesium

If the percent yield for the reaction is 79.9%, how many grams of product were recovered?

mass of product recovered: _________________ g

How many grams of the excess reactant remain?

mass of excess reactant:_____________

Answer 1

a)

balanced chemical equation :

2 Mg (s)   +   O2 (g)    -----------> 2 MgO (s)

b)

2 Mg (s)   +   O2 (g)    -----------> 2 MgO (s)

48.61 g          32 g                          80.61 g

4.20 g           6.75 g

48.61 g Mg   ------------> 32 g O2

4.20 g Mg   ------------> ??

mass of O2 needed = 4.20 x 32 / 48.61 = 2.76 g

here limiting reagent is = magnesium (Mg)

c)

theoretical yield = 4.20 x 80.61 / 48.61

                         = 6.96 g

% yield = 79.9 %

% yield = actual / theoretical yield ) x 100

79.9 = (actual / 6.96) x 100

mass of product recovered = 5.56 g

d)

here O2 is excess .

mass of excess reactant remain = 6.75 - 2.76 = 3.98 g

mass of excess reactant remain = 3.98 g