249 g of potassium iodide, KI, is mixed with 496.5 g of lead(II) nitrate, Pb(NO3)2. The equation of the reaction is represented below.

[Pb(NO3)2 = 331; KI = 166; PbI2 = 461, KNO3 = 101]

Calculate the number of moles of excess reagent left.

Give your answer to three significant figures.

The number of moles of excess reagent left is 0.750 moles

Explanation:

The number of moles is calculated by using the equation:

......(1)

Given mass of = 249 g

Molar mass of = 166 g/mol

Putting values in equation 1, we get:

Given mass of = 496.5 g

Molar mass of = 331 g/mol

Putting values in equation 1, we get:

The given chemical equation follows:

By stoichiometry of the reaction:

If 2 moles of KI reacts with 1 mole of lead(II) nitrate

So, 1.5 moles of KI will react with = of lead(II) nitrate

As the given amount of lead(II) nitrate is more than the required amount. Thus, it is present in excess and is considered as an excess reagent.

Thus, KI is considered a limiting reagent because it limits the formation of the product.

Moles of excess reactant () left = [1.5 - 0.75] = 0.750 moles

Hence, the number of moles of excess reagent left is 0.750 moles

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substituting a hydrogen atom with a halogen in a hydrocarbon:

- the single bond remains single. a is wrong.

- the bond with hydrogen is as strong as with a halogen. c is wrong

- a hydrocarbon is saturated if there is no double bond. we do not know that so d is wrong.

- carbon will always have four valence electrons. e is wrong.

by elimination, the correct answer is b. the boiling point of the new compound increases.