What Are Some Examples of a Stroichometry Problem?


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Stoichiometry is a branch of chemistry that deals with the relationship between reactants and products involved in a chemical reaction. In other words, it deals with calculations of masses or volumes of relative quantities of elements involved in a chemical reaction.

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Chemical reactions are often written as equations in chemistry, where the reactants appear on the left side of the equation, and the products appear on the right side. The following is a simple chemical equation:

2Na(s) + HCl(aq) ? 2NaCl(aq) + H2(g)

A chemical equation displays the ions, molecules and atoms of all the substances involved in the equation.

In chemistry, chemical equations are balanced through the stoichiometric coefficients. When a chemical equation is balanced, it means that both sides have an equal number of elements. A stoichiometric coefficient is the number that appears before the molecules, ions and atoms.

2 Na(s) + HCl(aq) ? 2NaCl(aq) + H2(g)

Stoichiometric problems are solved through the use of a stoichiometric coefficient. In the above chemical reaction, the stoichiometric coefficient is two. In a balanced equation, it is possible to compare varying elements through the ratio of stoichiometric coefficients. That is, the mole ratio between two elements involved in a chemical reaction is established through the stoichiometric coefficient ratio.

Here are some examples of stoichiometric problems:

Problem one: Write the molar ratios for N2 to H2 and NH3 to H2.

Problem two: Write the molar ratios for NH3 to N2 and H2O to O2.

Problem three: Hydroxylammonium chloride reacts with iron(III) chloride, FeCl3, in solution to produce iron(II) chloride, HCl, H2O and a compound of nitrogen. It was found that 2.00 g of iron(III) chloride reacted in this way with 31.0 mL of 0.200 M hydroxylammonium chloride. Suggest a possible formula for the compound of nitrogen so produced.

Problem 4: How many phosphate ions are in a sample of hydroxyapatite [Ca5(PO4)3OH] that contains 5.50 x 10-3 grams of oxygen?

Problem 5: Upon heating, a 4.250 g sample loses 0.314 grams. Assuming the sample is BaCl2 · 2H2O and NaCl, calculate the mass percent of BaCl2 · 2H2O.

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