Concept explainers
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 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 oxide UxOy is obtained if UO2NO3 · n H2O is heated to temperatures greater than 800 °C in air. However, if you heat it gently, only the water of hydration is lost. If you have 0.865 g UO2NO3 · n H2O and obtain 0.679 g UO2NO3 on heating, how many molecules of water of hydration were there in each formula unit of the original compound?
(a)
Interpretation:
A small sample of uranium metal is heated to
Explanation of Solution
Find moles of uranium and oxygen in sample:
Set up mole ratio:
Divide all the numbers in the ratio by the smallest number of moles,
2.6 is close to both 2.66 and 2.5, and since this number has an uncertainty of, either one is equally valid. It is unclear whether we should round down or up to find the whole number ratio. So, look at each case.
If the real ratio is
If the real ratio is ,we multiply by 2, and get
Of the two empirical formula of
(b)
Interpretation:
The oxide
Explanation of Solution
Mole ratio:
Divide by the smallest number of moles, 0.00204 mol, and round to whole numbers:
That means
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