St. Paul’s Secondary St. Paul’s Secondary SchoolSchool

Registration No. :BCh24開心漂白大發現開心漂白大發現

The Bleach FileThe Bleach File

IntroductionIntroduction•Types of Chlorine bleach:

1. KAO Bleach

2. Clorox Bleach

3. No Frills Bleach

4. LibY Bleach •Types of colour-safe bleach

1. Vanish in-wash stain remover (colour-safe)

2. KAO Liquid Wide Bleach.

•Working principles•Chemical content•Cleansing power towards different types of stains •Possible damages to cloth•Effect of mixing chlorine bleach and colour-safe bleach

Content Content

Chemical Content and Working PrincipleChemical Content and Working Principless o of Chlorine Bleach and Colourf Chlorine Bleach and Colour-S-Safe Bleachafe Bleach::

•Oxidizing power of the hypochlorous acid HOCl (aq) in chlorine bleaches

•Oxidizing power of hydrogen peroxide H2O2 (aq) in colour-safe bleaches.

HOCl (aq) + D H+ (aq) + Cl- (aq) + DO

H2O2 (aq) + D H2O (l) + DO

Coloured Colourless

Experiment 1

Aim:

To find out the active ingredient in chlorine bleaches and colour safe bleaches

I )To test for ClO- in chlorine bleaches:

Equation Involved:

OCl- (aq) + Cl- (aq) + 2H+ (aq) Cl2 (g) + H2O (l)

InvestigationInvestigation

Testing of the gas evolved after mixing chlorine bleach with

hydrochloric acid

II) To test for H2O2 in colour safe bleaches:

Equation involved:

2H2O2 (aq) O2 (g) + 2H2O(l)

Results:•A gas was evolved •The glowing splint relighted, which suggests that the gas is oxygen.

Conclusion:

Active ingredient in chlorine bleaches hypochlorite ions

Active ingredient in colour safe bleaches hydrogen peroxide

Experiment 2

Aim:

To determine the concentration of sodium hypochlorite in different brands of household chlorine bleaches.

To determine the concentration of sodium hypochlorite in different brands of household chlorine bleaches

Equations involved:

1) OCl- (aq) + 2I- (aq) + 2H+ (aq) I2 (g) + Cl- (aq) + H2O (l)

2) I2 (aq) + 2S2O32- (aq) S4O6

2- (aq) + 2I- (aq)

Titrated against S

2O32- (aq)

S2O32- (aq)

Colour change at end point: from blue to colourless

with starch added as indicator

Starch added

Diluted chlorine bleach, KI and H

2SO4

Brands of chlorine bleach

Molarity of NaOCl

Kao Bleach 2.2MClorox Bleach

2.12M

No Frills Bleach

1.99M

LibY Bleach 1.88M

Greatest molarity of NaOCl

Conclusion:

Brands of bleach

Price of bleach per mole of NaOCl

Kao Bleach $11.3

Clorox Bleach $6.21

No Frills Bleach $2.49

LibY Bleach $2.20

0

2

4

6

8

10

12

Kao Clorox No Frills LibY

Brands of chlorine bleach

Price per mole of NaOCl ($)

Best buy

Experiment 3

Aim:

To determine the concentration of hydrogen peroxide in different brands of colour-safe bleach

To determine the concentration of hydrogen peroxide in different brands of colour-safe bleach

Equation involved: 6H+

(aq) + 2MnO4- (aq) + 5H2O2 (l) 5O2 (g) + 2Mn2+ (aq) + 8H2O (l)

MnO4- (aq)

Colour change at the end point: from colourless to pale pink

Diluted colour-safe bleach

Brands of bleach

Molarity of H2O2

Price of bleach per mole of H2O2

Vanish Stain Remover

1.90M $10.6

Kao Liquid Wide Bleach

1.38M $13.0

Highest molarity of H2

O2

Best Buy

0

2

4

6

8

10

12

14

Vanish Kao

Brands of colour safe bleach

Price per mole of H2O2 ($)

02468101214

Kao

Clorox

No Frills

LibY

Vanish

Kao Liquid Wide

Price of the bleaches per number of moles of active ingredients in chlorine bleaches and colour-safe bleaches

Price per mole of active ingredient ($)

Chlorine bleaches Colour-safe bleaches

more expensive

Experiment 4

Aim: To investigate the cleansing power and possible damages to cloth of different chlorine/colour-safe bleaches.

Introduction: •Different kinds of cloths with different stains were soaked into different samples•Changes in textures and original colour of the fabrics, and the degree of removal of stains would be considered.

1.Curry stain

Purple cotton fabric Towel with curry stain with curry stain

2.Dark Soy Sauce Stain

Purple cotton fabric Towel with dark with dark soy sauce stain soy sauce stain

3.Black Ink Stain

Purple cotton fabric with black

ink stain

Towel with black ink stain

4.Ketchup Stain

Towel with ketchup stain

Purple cotton fabric with ketchup stain

5.Marker (Black) and Highlight Pen (Green) Stains

Purple cotton fabric with marker and

highlight pen stains

Towel with marker and

highlight pen stains

Analysis of Results:

1) Curry Stain

‘Kao Bleach’ bleached the curry stains most effectively.

2) Black Ink Stain

Colour-safe bleach bleached the black ink stain much better than chlorine bleaches.

3)  Dark Soy Sauce Stain

4)  Ketchup Stain

5)  Marker and Highlight Pen Stains

Similar performance on

6.White cotton fabrics

    One piece of white cotton fabric was dipped into each of the four different kinds of undiluted chlorine bleach for three days.

Result:

The pieces of white cotton fabric turned paler and thinner than the original sample.

KAO Bleach LibY Bleach No Frills Bleach

Original sample Clorox Bleach

7.Coloured checked fabrics

    One piece of coloured checked fabric was dipped into each of the two different kinds of colour-safe bleach for three days.

Result:

No obvious change in colour and texture.

Conclusion:

VANISH

The BEST stain remover:

Experiment 5

Aim:

To investigate the consequences of mixing household chlorine bleach and colour-safe bleach

Questions in mind: ??•What will happen if household chlorine bleach is mixed with colour-safe bleach? •Will the effectiveness of the bleaching action be increased upon mixing?

Colour-safe bleach Chlorine bleach

•High density white foam was evolved

•Heat was produced

The beaker of foam finally overflowed.

To collect the gas produced:

- by displacement of water`

Test result:

The glowing splint relighted which shows that the gas was oxygen.

Conclusion:•Redox reaction happened between hydrogen peroxide and hypochlorite ion.

Equations involved:

OCl-(aq) + H2O2(l) Cl-

(aq) + O2(g) + H2O(l)

(O.A.) (R.A.)

•An exothermic reaction•The oxygen formed causes the formation of the high density white foam.

Colour- safe bleach

Adding Chlorine Bleach

A lot of foam and heat are produced

Do you know how to choose

between chlorine bleach and colour safe bleach now?

St. Paul’s Secondary School

Registration No. :BCh24

Group members:

Ivy Yeung

Vivien Chu

Helen Kwai

Maggie Chow

Amelia Ho

Teacher Advisors:

Mrs. A. Lam

Miss I. Lau

•“Kao Bleach” has the highest concentration of hypochlorite ions among the four chlorine bleaches

•“Vanish Stain Remover” has the highest concentration of hydrogen peroxide among the two colour-safe bleaches.

•The best buy of chlorine bleach is “LibY Bleach” and that of colour-safe bleach is “Vanish”.

•“Vanish” was found to be the best stain remover among all brands of bleaches and it does not affect the original colour of the fabric.

•Chlorine bleach cannot be mixed with colour-safe bleach when use, or else they will lose their bleaching power and produce excess foam.

SummarySummary

DiscussionDiscussion 1. Pros and cons of using the 2 different

bleaches

Chlorine Bleach

Pros:

•cheaper and easily available.

•can be used as disinfectant.

•turns yellowish white fabrics back to its original

white colour.

•removes mildew on shower curtains, bath tubs, etc.

 

Chlorine Bleach

Cons:

•Chlorine is a toxic chemical.

•irritates eyes and skin.

•cannot be used on coloured fabrics

•cannot be used to bleach delicate fabrics such as silk.

•causes water pollution.

-  Environmental impact concerning the use of chlorine bleach:

Excessive use of bleaches may cause damage to the water pipes due to its corrosive nature.

Causes eutrophication in river and sea.

Toxic substances may produce and will stay in water and accumulate in the food chain.

H2O2 Bleach

Pros:

•H2O2 is a stronger oxidizing agent than NaOCl, the bleac

hing actions of H2O2 is faster, yet it does not cause any da

mage to fabrics.

•It is environmental friendly.

•The colour of fabrics being bleached will not lose its original colour.

H2O2 Bleach

Cons:

•Residual of H2O2 on clothes causes skin problems.

•It is more expensive than chlorine bleach.

•H2O2 is unstable and easily decomposes at high

temperature, thus it cannot be stored for a long period of time.

 

Further Investigation:

Possible factors affecting the bleaching power of the bleaches:

•Temperature

•pH values

How does bleach remove colour in organic compounds?

Colour in organic materials is the result of light absorption by certain chemical configurations called chromophores in molecules. C=C and C=O bonds are examples of chromophores. A chromophore, e.g. C=C and C=O, is a part of a molecule that is able to absorb UV light or visible light and producing colour in organic compounds.

Oxidizing bleaches break up these double bonds :

Reducing bleaches convert double bonds to single bonds:

HO

O

C C C C H

H

HO

C C OHH

O O

C C HOH

O

COLOURED

[O]

+

COLOURLESS

HO

O

C C C C H

H

HOH

CHCH2CH2CH2H

OH

COLOURED

[H]

COLOURLESS

Prices of different bleaches:

Kao Bleach : $14.9 per 600ml

Clorox Bleach : $7.9 per 710ml

No Frills : $9.9 per 2000ml

LibY Bleach : $6.2 per 1500ml

Prices of different colour-safe bleaches:

Vanish Stain Remover : $19.9 per 1kg

Kao Liquid Wide Bleach : $17.9 per 1000ml

E(V) Half equation

+0.68 O2 + 2H+ + 2e- H2O2

+ 0.89 ClO- +H2O + 2e- Cl- + 2OH-

+1.77 H2O2 + 2H+ + 2e- 2H2O2