Composition of potassium chlorate lab answers

LABORATORY 6

Revised SPR 2017

An impurity in a sample of KClO3

Guided Inquiry

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GENERAL INORGANIC CHEMISTRY I LABORATORY 6

An impurity 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. Your task 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 carry out an experimental procedure to determine the percent composition by mass of KCl (potassium chloride) in a mixture with KClO3 (potassium chlorate)

Learning Activities:

Pre-Lab

1. Read Lab 6.

2. Attempt Questions 1-14 on pages 103-104.

3. Print lab 7

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 the experiment 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. A Lab Report that is not initialed in the Checkout box may not be graded. It is at the discretion of your Lab Instructor.

4. Study for the Quiz next week.

Introduction

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

Chemical Properties:

KClO3 decomposes readily upon heating in the presence of the catalyst MnO2

to form KCl solid and O2 gas.

KCl solid does not decompose upon heating in 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

KClO3 white crystalline substance; soluble in water

If you need more information, consult the CRC Handbook of Chemistry and

Physics available 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 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 over the course of the reaction?

3. Does the mass of a sample of KCl at room temperature change upon heating and cooling back to 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. Explain the reasoning for your answer 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?

Lab 6 An impurity in a sample of KClO3

Calculations Worksheet

Complete this worksheet after answering questions 1-14.

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

1. Find the percent KCl in sample of the mixture of KCl and KClO3 given the following data:

Mass of test tube + MnO2

21.3567 g

Mass of test tube + MnO2 + KCl + KClO3

22.6219 g

Mass of KCl & KClO3 in original mixture

Constant mass* of test tube + reaction product

22.4511 g

Mass of O2 released

Moles of O2 released

Moles of KClO3 as required by moles of O2 released

Mass of KClO3 required

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 6 An impurity 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.