Today I will shed a light on the expiry date of Chlorine-based Bleach products. I hope, you know what are bleaches and also difference between bleach & bleaching powder – Here is an informative piece of writing about them.
Without wasting time, let’s get to the point :
(a) Liquid bleach (Sodium Hypochlorite) has a shelf life of 6 to 9 months.
(b) Bleaching Powder (containing calcium hypochlorite) – if kept intact in original production air-tight drum, then it will retain it’s effectiveness over a year ; if the seal is broken, it will remain in it’s initial strength for about 3 to 4 months in airtight container.
(c) However, upon dilution of bleach with water for disinfecting heavily infected hospital surfaces having spills of bodily fluid ( According to CDC, > 5000 ppm of hypochlorite is needed for this job. That means 1:10 dilution, in simpler calculation 100mL liquid bleach in 900 mL water. Handle with care as it is heavily caustic) or for household disinfection ( 1:84 to 1:100, depending on amount of available chlorine in your bleach & the type of object on which you are applying), this solution of bleach should be used within 24 hours.
(d) Same goes for shelf life of diluted bleaching powder, but it has way more available chlorine than bleach. WHO says in case of Bleaching powder, 1:10 dilution (for hospital use) will be 1 table spoon in roughly 2 Litre of water & 1:100 dilution (for household use) will be 1 table spoon in 20 Litre of water. Discard it after 24 hour.
What happens when bleaches reach their expiry date? Actually, they don’t expire at all, rather their effectiveness decreases over time. In room temperature, air & moisture can oxidise bleach products resulting in evolve of chlorine gas, hydrochloric acid or just salts – ultimately decompose bleaches & reduce their ability to clean:
(1) sodium hypochlorite reacts with air (carbon dioxide) to form sodium carbonate & gaseous chlorine:
2 NaOCl + CO2 ⟶ Na2CO3 + Cl2
(2) Sodium hypochlorite react with carbon dioxide and moisture to produce sodium bicarbonate and hypochlorous acid.
NaOCl + CO2 + H2O ⟶ NaHCO3 + HClO
Hypochlorous acid is unstable so it might decompose to give chlorine fumes or further react with hypochlorite to form chlorate.
OCl− + 2 HOCl ⟶ ClO3− + 2 HCl
(3) There is a slight possibility of decomposition to chlorate & chloride ; further decomposes to oxygen (with increasing temperature and under the influence of light and metals as copper, nickel, or cobalt):
2 NaOCl ⟶ NaClO2 + NaCl
NaOCl + NaClO2 ⟶ NaClO3 + NaCl
2 OCl− ⟶ 2 Cl− + O2
In a nutshell : You can use bleaching powder to clean & disinfect your household surfaces (not the metal ones!) by diluting 1 table spoon of powder into 20 Litre of water. Shelf life of this SOLUTION is of 24 hours. When bleaches complete their shelf life, amount of available chlorine in them may go down to it’s MEC ( Minimum Effective Concentration) value, and purpose of using bleach to disinfect surface or water purification get hampered.