GENERAL INORGANIC CHEMISTRY LABORATORY ASSIGNMENT: Animpurity in a sample of KClO₃

OBJECTIVE:

Scenario: The lab manager thinks that the KClO₃ to be used in an experiment has been contaminated with KCl. Yourtask is to determine the extent of contamination (if any) by measuring the percent composition by mass of KCl in the sample.

Objective: Work in pairs to design and carryout an experimental procedure to determine the percent composition by mass of KCl (potassium chloride) in a mixture with KClO₃ (potassium chlorate)

Learning Activities:

Lab

1. Complete Calculations Worksheet on page 105.

2. Design a procedure as described on page 107. You will use this procedure to carry out theexperiment next week.

3. Your Lab Instructor will initial the Title Page of Your Lab to indicate that you have attended the lab, completed the required lab activities, cleaned your lab bench and all equipment used, and returned all lab equipment to its designated space.

4. Study for the Quiz next week.

Introduction

Information below on the properties of the substances used in thislab will be helpful in designing and writing a procedure.

Chemical Properties:

KClO₃ decomposes 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 KClO₃ do not react with each other.

MnO₂,the solid catalyst,does not decompose upon heating.

Physical Properties:

KCl white crystalline substance; soluble in water

KClO₃white 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.

NOTES:

Guided Inquiry Questions

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 KClO₃in 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 KClO₃originally 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 KClO₃and KCl mixture?

Lab Animpurity inasample of KClO₃

Calculations Worksheet

Complete this worksheet after answering questions 1-14.

Using the following sample data gathered by heating the sample of KClO₃with KCl impurity until all oxygen in potassium chlorate (KClO₃)is driven off, calculate (show each step) the percentof KCl in a mixture of KCl and KClO3.

1. Find the percent KCl insample of the mixture of KCl and KClO₃given the following data:

Mass of test tube + MnO₂

21.3567g

Mass of test tube + MnO2+ KCl + KClO3

22.6219g

Mass of KCl&KClO3in original mixture

Constantmass* of test tube + reaction product

22.4511g

Mass of O₂ released

Moles of O₂ released

Moles of KClO₃ as required by moles of O₂ released

Mass of KClO₃required

Percent KClO₃ in sample of the mixture

2.If the actual amount of KClO₃ in the mixture is 0.5208 g what is the true percentage of KClO₃ in the mixture? Find percent error.

Lab Animpurity in a sample of KClO₃

Design a procedure to determine the percent composition by mass of KCl (potassium chloride) in a mixture with KClO₃ (potassium chlorate)

1. Draw a diagram or flow chart of your procedure.

2. Write a complete list of steps in your procedure.

3. Write a complete list of equipment needed.

4. Write a complete list of safety precautions for your procedure; look up the SDS data sheet for any potentially harmful substances.

5. What are potential sources of error in this experiment?

6. Obtain instructor approval, as indicated by his/her signature below, for your procedure and your pre-lab preparations. Your procedure must be signed and approved by you Lab Instructor before you begin any experimental work lab work next week.