How do I write/fill this questions?

Question

Q1. Write the balanced equation for the decomposition of KClO3 in the presence of a catalyst. The products of the reaction are KCl and O2.

 The answer is 2KClO3 ----> 2KCl + 3O2 ?

Q2. What is the function of a catalyst in a chemical reaction; does the mass of the catalyst change over the course of the reaction?

Q3. 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?

The mass is the same after heating. Is it the correct answer? 

Q4. Explain the reasoning for your answer to question 4; what substance undergoes a change in mass upon heating?

Q5. What gaseous substance is evolved and leaves the open test tube upon heating?

Q6. What is meant by heating to constant mass*?

Q7. How, in the lab, can you determine if the sample in the test tube has attained constant mass?

Q8. Why is important that the sample in the test tube has attained constant mass after repeated heating/cooling cycles?

Answer 1

Hello, Ooyeon,

Q1. Yes, the equation is balanced. Thanks for doing that.

Q2. A catalyst accelerates/promotes a reaction. It is incorporated in any of the products.

Q3. I'm assuming that they are referring to the mass remaining in the test tube. If so, the mass is lower since it does not include the O2 that has escaped the system. If they meant to include the O2, then, yes, the mass would be the same. But I suspect they are looking only at the mass in the test tube.

Q4. As per my reasoning in Q3, the O2 escapes and is no longer part of the system. The starting material undergoes a change in mass since it decomposes.

Q5. Oxygen

Q6. Don't stop heating until the end of the reaction is reached, that is, no more starting material decomposes.

Q7. Not sure. Just keep weighing it and putting it back on the heat? Or perhaps if you suspended the tube from a balance and monitored the mass change.

Q8. It actually depends on the purpose of the experiment. If it is to study the composition of an unknown material, the complete reaction would help determine the % O2, for example. If the purpose is just to make O2, then it doesn't matter, unless you change by the gram.

Bob