3. How many grams of
CoCl, in 1/2 Liter would be
used to make a 1.0 molar
solution?

47 grams CoCl needed.

Explanation:

1 mole weight of CoCl in 1 Liter solution => 1.0 molar solution

∴ 1/2 mole weight of CoCl in 1/2 Liter solution => 1.0 molar solution.

1/2 mole weight of CoCl = 1/2(94 g/mole) = 47 grams CoCl needed.  

When a Magnesium Ribbon is burnt, a powdery substance called magnesium oxide is formed.

Explanation:

There has obviously been a chemical change because several chemical properties of the magnesium have been modified:  the color, the texture and the mass.

The increase in mass is due to the fact that oxygen from the air has combined with the magnesium to make magnesium oxide, MgO.

The chemical equation, Mg + O2  MgO shows this reaction but it needs to be balanced to make 2Mg + O2  2MgO.  

Using stoichiometry, we can convert this eqation into an equation with moles:  

2 mol Mg + 1 mol O2  2 mol MgO.  

Next, we convert to grams using atomic masses obtained from the periodic table:

48g Mg + 32g O2  80g MgO

Lastly, we determine the same thing in the proportions we used.  In other words, we used only 0.15g of Mg (not 48g) so everything needs to be divided by 320.  So 80 / 320 = 0.25 g.  If we burn 0.15 g of Mg, we obtain 0.25 g of MgO.

Hope this helps!!!

This is my first answer.