Redox - experiment

Question 1

What is effervescence?

Answer 1

bubbles produced

Question 2

Experiment!
Pour 1cm3 of aq hydrogen peroxide in a test tube, add a small amount of manganese(IV) oxide. Test the gas evolved with a glowing splint

chemical equation? – assign OS
observations?

Answer 2

manganese(IV) oxide MnO₂ -> catalyst

2 H₂O₂ (aq) -> 2 H₂O (l) + O₂ (g)
+1 -1 +1 -2 0
observations:
Effervescence of a colourless, odourless gas produced.
Gas produced relights a glowing splint

Question 3

What is a catalyst?

Answer 3

speeds up reaction but remains chemically unchanged

Question 4

Experiment qn!

Explain why a small volume of reagent is preferred for testing instead of a large volume?

Answer 4

This is to ensure that the reagents can be mixed easily for complete reaction to obtain visible results.

• might see diff in colour -> reaction only happen on surface

Question 5

Experiment qn!

Predict the observations made when aq potassium iodide reacts with aq iron(II) sulfate and explain your answer.

Answer 5

observation: no visiable reaction
explanation: Both aq potassium iodide and aq iron(II) sulfate are RA. Thus no redox reaction occurred.

Question 6

Experiment qn!
Outline a method to test for presence of an OA. Include in your answer the measurements you would take, and explain how your results show whether there is an oxidising agent present.

Answer 6

Add 1m³ of aq potassium iodide (I⁻) to the unknown solution.
The solutions will turn from colourless to brown when it reacts with an OA
The potassium iodide (I⁻) has been oxidised to form iodine (I₂) thus, oxidising agent is present.

Note: need to use a colour changing RA to test for an OA

Question 7

Experiment qn!
test tube have unknown substance, unknown substance OA? 
Add RA
colour change occurs? 
no visiable change? 
conclusion

Answer 7

colour change: OA is present in test tube

no visible change: OA is not present

Question 8

Experiment qn!

Hydrogen peroxide is used in three different reaction. What is the unique property of it?

Answer 8

Hydrogen peroxide can be both an OA and RA at the same time.

Question 9

Experiment qn!
Both SO₃ ²⁻ and SO₂ are good RA. Identify the common feature that makes them behave similarly in redox reactions?
(talk about electrons and OS)

Answer 9

Both are willing to lose electrons to other substances.
The oxidation state of sulfur in both SO₃ ²⁻ and SO₂ can be increased from +4 to +8.

SO₃ ²⁻ -> SO₄²⁻
+4 +8
SO₂ -> SO₄²⁻
+4 +8