   Chapter 2, Problem 156GQ

Chapter
Section
Textbook Problem

Uranium is used as a fuel, primarily in the form of uranium(IV) oxide, in nuclear power plants. This question considers some uranium chemistry.(a) A small sample of uranium metal (0.169 g) is heated to between 800 and 900 °C in air to give 0.199 g of a dark green oxide, UxOy How many moles of uranium metal were used? What is the empirical formula of the oxide, UxOy? What is the name of the oxide? How many moles of UxOy must have been obtained?(b) The naturally occurring isotopes of uranium are 234U, 235U, and 238U. Knowing that uranium’s atomic weight is 238.02 g/mol, which isotope must be the most abundant?(c) If the hydrated compound UO2(NO3)2 · z H2O is heated gently, the water of hydration is lost. If you have 0.865 g of the hydrated compound and obtain 0.679 g of UO2(NO3)2 on heating, how many waters of hydration are in each formula unit of the original compound? (The oxide Ux, Oy is obtained if the hydrate is heated to temperatures over 800°C in the air.)

(a)

Interpretation Introduction

Interpretation: The moles of uranium, empirical formula of oxide UxOy, name of UxOy and the moles obtained should be determined under given conditions.

Concept introduction:

• Empirical formula of a compound represents the smallest whole number relative ratio of elements in that compound.
• Equation for number moles from mass and molar mass,

Numberofmoles=MassingramsMolarmass

• Mass percent of elements of a compound is the ratio of mass of element to the mass of whole compound and multiplied with hundred.
• Isotopes are atoms of the same element having the same number of protons but different number of neutrons.
• The molar mass of an element or compound is the mass in grams of 1 mole of that substance, and it is expressed in the unit of grams per mole (g/mol).
Explanation

Here,

A small sample of uranium metal (0.169 g) is heated to between 800and9000C in air to give 0.199g of product UxOy

Then the amount of uranium used in this process can be calculated as follows,

Massofuraniummetal=0.169gMolarmassofuranium=238.02g/molAmountofuranium=0.169g238.02g/mol =7.1×10-4mol

Massofoxygenreacted =0.199g0.169g =0.030gMolesofoxygenreacted =0

(b)

Interpretation Introduction

Interpretation: The most abundant isotope from naturally occurring isotopes should be identified using given atomic weight of uranium.

Concept introduction:

• Empirical formula of a compound represents the smallest whole number relative ratio of elements in that compound.
• Equation for number moles from mass and molar mass,

Numberofmoles=MassingramsMolarmass

• Mass percent of elements of a compound is the ratio of mass of element to the mass of whole compound and multiplied with hundred.
• Isotopes are atoms of the same element having the same number of protons but different number of neutrons.
• The molar mass of an element or compound is the mass in grams of 1 mole of that substance, and it is expressed in the unit of grams per mole (g/mol).

(c)

Interpretation Introduction

Interpretation: The waters of hydration in each formula unit of original given compound should be identified by using given data.

Concept introduction:

• Empirical formula of a compound represents the smallest whole number relative ratio of elements in that compound.
• Equation for number moles from mass and molar mass,

Numberofmoles=MassingramsMolarmass

• Mass percent of elements of a compound is the ratio of mass of element to the mass of whole compound and multiplied with hundred.
• Isotopes are atoms of the same element having the same number of protons but different number of neutrons.
• The molar mass of an element or compound is the mass in grams of 1 mole of that substance, and it is expressed in the unit of grams per mole (g/mol)

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