Common Chemical Compounds and Reactions

Dry ice is the solid form of carbon dioxide (CO2). It sublimates directly from solid to gas at -78.5°C without passing through the liquid phase, which is why it's called 'dry' ice. Sodium carbonate (washing soda) and ammonium chloride are different compounds entirely.

Sodium chloride (NaCl) acts as an accelerator for the setting of Plaster of Paris. When NaCl is added to the plaster slurry, it increases the rate of hydration and causes faster setting by providing additional ions that speed up the crystallization process.

Gypsum is added to cement to retard or slow down its setting time. This is crucial for construction applications where extended workability is needed. Gypsum controls the flash setting of cement by reacting with C3A (tricalcium aluminate) to form ettringite, preventing immediate hardening.

Gypsum is calcium sulphate dihydrate (CaSO4·2H2O). It's a soft sulfate mineral used in plaster, wallboard, and fertilizer.

Soda water is carbonated water containing dissolved carbon dioxide, which forms carbonic acid (H2CO3). This gives it a slightly acidic taste and effervescence.

Pearl ash (Potassium carbonate) = K₂CO₃

Foam fire extinguishers contain aluminium sulphate solution in one chamber and sodium bicarbonate solution in another. When mixed, they react to form aluminium hydroxide foam and carbon dioxide, which smothers the fire by excluding oxygen. Copper, cobalt, and nickel sulphates are not used in foam extinguishers.

Common salt (table salt) is chemically known as sodium chloride (NaCl). It is an ionic compound composed of sodium cations and chloride anions. Sodium nitrate is a different salt used in fertilizers and food preservation. Ammonium chloride has different applications. Calcium chloride is used for de-icing and dust control.

Sodium hypochlorite is most commonly used solution for irrigation of root canals.

Sodium hypochlorite is the recommended disinfectant for cleaning blood spills because it is a broad-spectrum antimicrobial effective against bloodborne pathogens including HBV and HIV. It's inexpensive, readily available, and acts quickly. Iodine is not typically used for environmental decontamination of blood. Absolute alcohol is not effective against all bloodborne pathogens. Quaternary ammonium compounds may not be effective against certain viruses and are not the first choice for blood spills.

Sodium hypochlorite (bleach) is the recommended disinfectant for cleaning blood spills because it is effective against bloodborne pathogens including HIV and hepatitis B and C. It is inexpensive, readily available, and has broad-spectrum antimicrobial activity. Iodine, alcohol, and quaternary ammonium compounds are not the first choice for blood spill decontamination.

KNaCO3 (potassium sodium carbonate) is a double salt. Double salts are compounds that contain two different cations that crystallize together in a fixed ratio. The other options are simple single-cation salts.

Plaster of Paris is calcium sulfate hemihydrate, represented as CaSO4·1/2H2O, meaning each calcium sulfate unit is associated with half a water molecule. It's produced by heating gypsum (CaSO4·2H2O) to about 150°C, which drives off about 1.5 water molecules per unit. When mixed with water, it rehydrates to form gypsum, creating a hard solid - the basis for casts and molds.

Soaps are produced through saponification - the reaction between fats/triglycerides and strong alkalis like sodium hydroxide (NaOH) or potassium hydroxide (KOH). This process produces glycerol and soap salts. The other options are incorrect because alcohols, acids, or water alone cannot convert fats into soap.