Question 7: Stoichiometry (3 points) Unit 5
a. How is stoichiometry used to calculate amounts of substances in a chemical reaction? (1 point)

b. Use the balanced equation to answer the following questions. (2 points)
CuSO4(aq) + 2NaOH(aq) Cu(OH)2(s) + Na2SO4(aq)

i. What is the ratio of moles of CuSO4 to moles of NaOH? (.5 point)

ii. If 638.44 g CuSO4 reacts with 240.0 NaOH, which is the limiting reagent? (.5 point)

iii. Use the limiting reagent to determine how many grams of Cu(OH)2 should precipitate out in the reaction. (.5 point)

iv. If only 174.6 g of Cu(OH)2 precipitate were actually collected from the reaction, what would the percent yield be? (.5 point)

answer: - first one is the correct answer. .

explanations: - potassium sulfide is and cobalt(ii) chloride is .

charge on k is +1, charge on s is -2, charge on co is +2 and charge on cl is -1.

in a double replacement reaction the ion exchange takes place. in general the reaction looks like:

if one of the product is insoluble as per solubility rules then a precipitate of it is formed.

when we mix the aqueous solutions of potassium sulfide and cobalt(ii) chloride then chloride ion goes with potassium ion and sulfide ion goes with cobalt ion and the balanced equation is written as:

k and cl has equal charges, similarly co and s has equal charges and hence no subscripts are used for the product side.

as per the solubility rules, cos is insoluble and so it's precipitate is formed.

looking at the given choices, first choice is correct.