Lab 6D

    So today we did a lab which is determining the limiting reactant and percent yield in a precipitation reaction. The objectives are to observe the reaction between solutions of sodium carbonate and calcium chloride; To determine which of the reactants is the limiting reactant and which is the excess reactant; to determine the theoretical mass of precipitate that should form and to compare the actual mass with the theoretical mass of precipitate and calculate the percent yield.

Stoichiometry Exercise

Is a branch of chemistry that deals with the quantitative relationships that exist between the reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers. For example, in a reaction that forms ammonia (NH₃), exactly one molecule of nitrogen (N₂) reacts withc)  three molecules of hydrogen (H₂) to produce two molecules of NH₃:

N₂ + 3H₂ → 2NH₃

Example 1 : Ca(s) + 2HCl(aq) ----> CaCl2(aq) + H2(g)

a) How many atoms of Ca are needed to produce 1 molecule og Hydrogen?
Ans : Base on the equation : 1 mole of Ca/1 mole of Hydrogen = 1

b) How many moles of HCl are needed to produce 0.452 moles of CaCl2?

Ans : 0.452Ca x 2 moles of HCl/1 mole of Ca = 0.904mol

c) How many grams of Ca will react with 1.05moles of HCl?

Ans : 1.05moles of HCl x 1mole of Ca/2Hcl = 0.525moles of Ca

d) How many grams of CaCl2 will be formed when 2.00g of hydrogen is formed?

Ans : 2.00g/2 moles of H2 x 1 mole of CaCl2/1 mole of H x (40.1 + 35.5 x 2)g = 111.1gCaCl2

e) How many moles of of HCl are needed to form 6.12grams of CaCl2?

Ans : 6.12g of CaCl2/(40.1 + 35.5 x 2)mol of CaCl2 x 2 moles of HCl/1 mole of CaCl2 = 0.11 mol of HCl

Chapter 6 - Stoichiometry

  
As the definition above, Stoichiometry deals with quantitative analysis of chemical reactions, it is also the relationship between reactants used and products produced. It can use as molecules AND moles; it can also be used as conversion factors. The coefficient in balanced equations tell us the number of moles reacted or produced.

Stoichiometry calculations can predict how elements and components diluted in a standard solution react in experimental conditions. Stoichiometry is founded on the law of conservation of mass: the mass of the reactants equals the mass of the products.

A stoichiometric amount or stoichiometric ratio of a reagent is the amount or ratio where, assuming that the reaction proceeds to completion:

1. all reagent is consumed,
2. there is no shortfall of reagent, and
3. no residues remain.

Here is a little video that i found on youtube that could help you understand more about Stoichiometry - http://www.youtube.com/watch?v=rESzyhPOJ7I