Question

CHIOMETRY: CHEMICAL REACTION CALCUATIONS: merical relationship among the reactants and products in a balanced equation (Chemic- For example: Two magnesium atoms (a solid) when ignited, reacts with oxygen atoms to form eaction) The Balanced equation A balanced equation shows a chemical reaction in shorthand: magnesium oxide The meaning of a balanced Chemical Equation: A bookkeeping system The balanced equation- mole to mole ratios These mole to mole ratios are exact numbers. II. The Stoichiometric Pathway: # of particles of Known # particles of U Avo. # Avo. # balanced equation Moles of Unknown. Moles of Known molar,mass molar mass Grams of Un Grams of Kn own . Stoiciometric Calculations he reaction: Key: You must have a balanced equation!! Chromium metal is reacted with copper (II) chloride 3 G+a GCI3 aGcls6-omol GCs mol g How many grams of chromic chloride are produced from 6.0 mole Cr? a Cr+3CuCh 6.0moleC 159.998 CCla X 959-94 mol GCla HAat &ia 2co,9+= w many grams of oxygen gas are required for the complete combustion of 694 cample of natural gas? Gomol GClg x

Answer 1

The balanced chemical equation is :

ZnCl₂ (aq) + 2 NaOH (aq) = Zn (OH)₂ (s) + 2 NaCl (aq)

Moles of ZnCl₂ used = Mass / Molar mass = 13 g / ( 136.286 g / mole) = 0.0953 mole

Moles of NaOH = Mass/ Molar mass = 17 g / ( 40 g / mole) = 0.425 mole

According to stoichiometry,

0.0953 moles of ZnCl2 reacts with 2 * 0.0953 moles = 0.1906 moles of NaOH. But in the reaction, 0.425 moles of NaOH has been employed.

So, NaOH is excess reagent. Since all ZnCl2 is used in the reaction, it is the limiting reagent.

(b) The moles of product [Zn(OH)2] produced = moles of LR (ZnCl2) reacted = 0.0953 mole

Mass of the product = 0.0953 mole * 99.424 g / mole = 9.48 g

(c) Moles of excess reagent left = 0.425 - 0.1906 moles = 0.2344 mole

mass of excess reagent left = 0.2344 moles * 40 g/ mole =9.38 g