Page 10 26. In a UK workplace, the maximum short-term exposure limit for carbon monoxide is 200 ppm in a 15 minute period. If a person breathes in 134 g of air in a 15 minute period, what is the mass of carbon monoxide breathed in at the maximum short-term exposure limit? A 1·49 mg B 26·8 mg C 1·49 g D 26·8 g 27. Sodium hydroxide is unsuitable for use as a primary standard because it A is corrosive B is readily soluble in water C is available in a high degree of purity D readily absorbs water from the atmosphere. 28. What volume of 0·25 mol l−1 calcium nitrate is required to make, by dilution with water, 500 cm3 of a solution with a nitrate ion concentration of 0·1 mol l−1? A 50 cm3 B 100 cm3 C 200 cm3 D 400 cm3 29. 1·60 g of an anhydrous metal sulfate were dissolved in water. Addition of excess barium chloride solution resulted in the precipitation of 2·33 g of barium sulfate. The original substance was A copper(II) sulfate B magnesium sulfate C sodium sulfate D calcium sulfate.