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University of Toronto

Problem 70

Potassium nitrate decomposes on heating, producing potassium oxide and gaseous nitrogen and oxygen:

$$

4 \mathrm{KNO}_{3}(s) \longrightarrow 2 \mathrm{K}_{2} \mathrm{O}(s)+2 \mathrm{N}_{2}(g)+5 \mathrm{O}_{2}(g)

$$

To produce 56.6 $\mathrm{kg}$ of oxygen, how many (a) moles of $\mathrm{KNO}_{3}$

and (b) grams of $\mathrm{KNO}_{3}$ must be heated?

Answer

a)

$\mathrm{n}\left(\mathrm{KNO}_{3}\right)=1415 \mathrm{mol}$

b)

$\mathrm{m}=\mathrm{n}^{*} \mathrm{Mr}=142929,15 \mathrm{g}=1,43^{*} 10^{5} \mathrm{g}$

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## Discussion

## Video Transcript

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## Recommended Questions

On heating, potassium chlorate ( $\mathrm{KClO}_{3}$ ) decomposes to yield potassium chloride and oxygen gas. In one experiment, a student heated $20.4 \mathrm{g}$ of $\mathrm{KClO}_{3}$ until the decomposition was complete.

(a) Write a balanced equation for the reaction. (b) Calculate the volume of oxygen (in liters) if it was collected at 0.962 atm and $18.3^{\circ} \mathrm{C}$.

Nitrogen can be produced from sodium metal and potassium nitrate by the reaction:

$$

10 \mathrm{Na}(s)+2 \mathrm{KNO}_{3}(s) \rightarrow \mathrm{K}_{2} \mathrm{O}(s)+5 \mathrm{Na}_{2} \mathrm{O}(s)+\mathrm{N}_{2}(g)

$$

If we generate oxygen by the thermal decomposition of potassium chlorate:

$$

2 \mathrm{KClO}_{3}(s) \rightarrow 2 \mathrm{KCl}(s)+3 \mathrm{O}_{2}(g)

$$

how many grams of potassium nitrate and how many grams of potassium chlorate would be needed to make $200.0 \mathrm{L}$ of gas containing $160.0 \mathrm{L}$ of $\mathrm{N}_{2}$ and $40.0 \mathrm{L}$ of $\mathrm{O}_{2}$ at 1.00 atm and $290 \mathrm{K} ?$

A common laboratory preparation of oxygen gas is the thermal decomposition of potassium chlorate (KClO $_{3}$ ). Assuming complete decomposition, calculate the number of grams of $\mathrm{O}_{2}$ gas that can be obtained from $46.0 \mathrm{g}$ of $\mathrm{KClO}_{3}$. (The products are $\left.\mathrm{KCl} \text { and } \mathrm{O}_{2} .\right)$

Ammonium nitrate decomposes explosively upon heating according to the balanced equation:

$$

2 \mathrm{NH}_{4} \mathrm{NO}_{3}(s) \longrightarrow 2 \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g)

$$

Calculate the total volume of gas (at $25^{\circ} \mathrm{C}$ and $748 \mathrm{mm} \mathrm{Hg}$ ) produced by the complete decomposition of $1.55 \mathrm{kg}$ of ammonium nitrate.

Write balanced equations for the thermal decomposition of potassium nitrate ($\mathrm{O}_{2}$ is also formed in both cases): (a) at low temperature to the nitrite; (b) at high temperature to the metal oxide and nitrogen.

Ammonium nitrate decomposes explosively upon heating according to the balanced equation:

$$2 \mathrm{NH}_{4} \mathrm{NO}_{3}(\mathrm{s}) \longrightarrow 2 \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g)+4 \mathrm{H}_{2} \mathrm{O}(g)$$

Calculate the total volume of gas (at $125^{\circ} \mathrm{C}$ and 748 $\mathrm{mm} \mathrm{Hg}$ ) produced by the complete decomposition of 1.55 $\mathrm{kg}$ of ammonium

nitrate.

A laboratory method of preparing $\mathrm{O}_{2}(\mathrm{g})$ involves the decomposition of $\mathrm{KClO}_{3}(\mathrm{s})$

$$2 \mathrm{KClO}_{3}(\mathrm{s}) \stackrel{\Delta}{\longrightarrow} 2 \mathrm{KCl}(\mathrm{s})+3 \mathrm{O}_{2}(\mathrm{g})$$

(a) How many moles of $\mathrm{O}_{2}(\mathrm{g})$ can be produced by the decomposition of $32.8 \mathrm{g} \mathrm{KClO}_{3} ?$

(b) How many grams of $\mathrm{KClO}_{3}$ must decompose to produce $50.0 \mathrm{g} \mathrm{O}_{2} ?$

(c) How many grams of KCl are formed, together with $28.3 \mathrm{g} \mathrm{O}_{2},$ in the decomposition of $\mathrm{KClO}_{3} ?$

Potassium nitrite can be produced by heating a mixture of potassium nitrate and carbon. Write a balanced equation for this reaction. Calculate the theoretical yield of $\mathrm{KNO}_{2}$ produced by heating $57.0 \mathrm{g}$ of $\mathrm{KNO}_{3}$ with an excess of carbon.

Potassium nitrite can be produced by heating a mixture of potassium nitrate and carbon. Write a balanced equation for this reaction. Calculate the theoretical yield of $\mathrm{KNO}_{2}$ produced by heating $57.0 \mathrm{g}$ of $\mathrm{KNO}_{3}$ with an excess of carbon.

When heated, solid potassium chlorate $\left(\mathrm{KClO}_{3}\right)$ decomposes to form solid potassium chloride and oxygen gas. If 20.8 $\mathrm{g}$ of potassium chlorate decomposes, how many liters of oxygen gas will form at STP?