Corrosives 10/6/2016 AIMS. Terminology. Aim. Acid Base Alkali Proton

Transcription

1 Corrosives Class 8 substances and similar materials AIMS Aim To identify the class specific Hazards and control measures associated with class 8 substances Objectives Develop understanding in the concept of acid and base Highlight operational considerations Understand the methods of quantifying toxicity Terminology Acid Base Alkali Proton 1

2 Identification UN Number Hazard warnings MSDS Name Sulphuric Acid Caustic Potash Identification Acids and Bases have a more practical means of identification ph paper Use it Dry for liquids Use it wet for gasses and solids Behavior Corrosives mostly fall in to 2 main types Acids Sour Good at dissolving Proton Donators Bases Bitter Good at dissolving Proton Acceptors ph scale <7=acid >7=base 2

3 Acid what is it Acids are proton donators hydrogen ion donators Can only exist in water Water acts like a middle man dissolving the acid It dissociates into a H + and a negative ion (e.g. CL - Chloride ion) Hydrogen Chloride (HCL) vs Hydrochloric Acid (HCL) WATER ph Is a measure of Hydrogen ions (H + ) in water In water, molecules of H 2 O can ionize H 2 O becomes H + and OH - This is very rare!!! 1 in 10,000,000 or 1 in 10-7 ph 7 3

4 1 in 10 million - molecules is H + - ph 7 Apples ph 3 or 1 in 10-3 H + or 1 in 1,000 H + Still not very many!!! Bases (Alkali) Sodium Hydroxide in water NaOH dissociates Na + and OH - Once in water OH - can combine with any naturally forming H + making them even more rare!!! E.g. concentrated NaOH Chance of H + is 1 in 100 trillion 1 in 100,000,000,000,000 or ph 14 ph 0 for strong acids is achieved at low concentrations As concentration increases the ph cannot get any lower! 4

5 Strength vs Concentration Concentrated vs Dilute Acids ph scale is only useful for dilute acids Both 40% and 4% HCl will be ph 0 How practically can we determine if we have a concentrated or dilute acid? Weak vs Strong acids 5

6 Weak / Strong Acids Strong/Weak vs Concentrated/Dilute 4% HCL total dissociation therefore 4% H + vs Acetic acid only 4% of the molecules will dissociate so: For acetic acid, 96 out of 100 molecules will be as CH 3 COOH and only 4 will be CH 3 COO - H + 40% acetic will only give 40x4% or 1.6% H + Strong Acids Sulphuric Acid Hydrochloric Acid Nitric Acid Hydrofluoric acid Weak Acids Ethanoic Acid Acetic Acid Oxalic Acid Carboxylic Acid Organic Acids Weak Other hazards Flammable? Maybe Combustible? Yes if not much water (water content) 6

7 Acids Strong Diluted Stomach acid Hydrochloric 2% Concentrated Battery acid Sulphuric 40% Weak Diluted Vinegar Acetic Acid 7% Concentrated Citric Acid powder 100% Comparison of vinegar and hydrochloric acid Comparison of 2 concentrations of hydrochloric acid 7

8 Practical Please remember Acid into water not water into acid Why? Application Strong acid / Weak acid Ability to give up hydrogen ion High / Low Concentration 38% HCl - Corrosive 10% HCl Irritant 3% HCL not hazardous under regs Metals Secondary Hazards Hydrogen generation Oxidising Flammable Toxic Explosive Water reactive Heat, vapour produced Release of toxic vapours 8

9 Uses Drain Cleaner Battery acid Industrial scrubbers Fertiliser manufacture Sulphuric Acid Hazards Mild oxidizing agent High heat release with water Corrosive to metals Nitric Acid Uses Fertilisers Metallurgy Gold recovery Hazards Oxidiser Liable to liberate fume Chromic Acid Uses Ceramic Glazes Metal plating Hazards Oxidiser Carcinogenic 9

10 Hydrochloric Acid Uses PVC manufacture Descaler Hazards Corrosive to metals Hydrofluoric Acid Uses Glass Etching PTFE Teflon Dosing for water Hazards Toxic Calcium scavenger Other Common Corrosives Calcium oxide Calcium Hydroxide Sodium Hydroxide Ammonia (anhydrous and solution) Carbonate Acetic acid Peracetic acid Amines Picric acid 10

11 Corrosive Vapours Acid gasses Basic gasses Combustion products Potential trace (or not so trace) elements common in certain fires S SO 2 H 2 SO 4 P PO 5 H 3 PO 4 N NO 2 (brown fumes) HNO 3 N Cl HCL F HF C CO or CO 2 Reaction with metals Aluminum Steel (some types are passive) acids corrode metals to form an atmosphere containing a flammable proportion of hydrogen, especially in a confined space where appropriate precautions will be demanded. 11

12 Neutralization Become salts Only loose the corrosive property Still may be hazardous Materials Examples Nitrates still oxidizing Fluorides still toxic Operations Contain and Recover Contain and Absorb Contain and Neutralise Dilute and Disperse Operations Transport is normally in very high concentrations Corrosives attack many materials, e.g. Cloth, paper, metal Effects can be delayed 12

13 Operations In the case of strong alkalis there is a latent period before a feeling of burning on the skin is experienced. By then the damage is already done. Skin contact with strong acids produces an immediate feeling. Both types of corrosive substances can cause serious skin and eye damages. Accidental mixing of different corrosive materials can in some cases lead to violent reactions, which may give off large amounts of gases Water into very concentrated acid will also produce heat, producing acid vapours and increasing corrosive reactions Questions 13