Assignment: Chemical Properties

KClO₃decomposes readily upon heating inthe presence of the catalyst MnO₂ to form KCl solid and O₂gas.
KCl solid does not decompose upon heatingin the presence of catalyst MnO₂.
KCl and KClO₃do not react with each other.
MnO₂,the solid catalyst,does not decompose upon heating.

Physical Properties:

KCl white crystalline substance; soluble in water
KClO₃ white crystalline substance; soluble in water
If you need more information, consult theCRC Handbook of Chemistry and Physicsavailable via data base from the HCC Library. Your instructor can also borrow a copy from the chemistry prep room.

GuidedInquiryQuestions (Short answers )

Answer the following questions in complete sentences. The questions are designed to prompt your thoughts about the design of your experiment and data collection sheet.

1. Write the balanced equation for the decomposition of KClO₃ in the presence of a catalyst. The products of the reaction are KCl and O₂.

2. What is the function of a catalyst in a chemical reaction; does the mass of the catalyst change overthe course ofthe reaction?

3. Does the mass of a sample of KCl at room temperaturechange upon heating and cooling backto room temperature?

4. If you heat a mixture of the two compounds, KCl and KClO₃ ,in the presence of MnO₂(catalyst) in an open test tube, is the mass of the mixture before heating larger than,smaller than, or unchanged from, the mass after heating?

5. Explainthereasoningforyouranswer to question 4; what substance undergoes a change in mass upon heating?

6. What gaseous substance is evolved and leaves the open test tube upon heating?

7. How can we determine the number of grams of the gaseous substance evolved in question 6?

8. How can we determine the number of moles of the gaseous substance evolved in question 6?

9. How does the number of moles of the gaseous substance evolved relate to the number of moles of KClO₃ originally present in the mixture?

10. What is meant by heating to constant mass*?

11. How, in the lab, can you determine if the sample in the test tube has attained constant mass?

12. Why is important that the sample in the test tube has attained constant mass after repeated heating/cooling cycles?

13. How can we determine the number of moles and grams of KClO₃ originally present in the mixture?

14. How can we determine the percent of KClO₃ in the KClO₃ and KCl mixture?