A water sample has a TDS concentration of 425 mg/L and a specific conductivity of 32 µS. Which statement best describes the solids?

A water sample has a TDS concentration of 425 mg/L and a specific conductivity of 32 µS. Which statement best describes the solids?

• A. ionic solids
• B. approximately equal amounts of ionic and nonionic solids
• C. cannot be determined
• D. nonionic solids

Answer: (D)

TDS and conductivity measure different things in water: TDS tallies all dissolved solids by weight, while conductivity reflects how many free ions are present to carry electric current. Here, a TDS of 425 mg/L comes with a relatively low conductivity of 32 µS/cm. If most of the dissolved material were ionic, those ions would produce much higher conductivity for that amount of dissolved solids. The comparatively low conductivity indicates few ions are formed, so the dissolved solids are predominantly nonionic. This fits the idea that nonionic substances can raise TDS without contributing much to conductivity.

TDS and conductivity measure different things in water: TDS tallies all dissolved solids by weight, while conductivity reflects how many free ions are present to carry electric current. Here, a TDS of 425 mg/L comes with a relatively low conductivity of 32 µS/cm. If most of the dissolved material were ionic, those ions would produce much higher conductivity for that amount of dissolved solids. The comparatively low conductivity indicates few ions are formed, so the dissolved solids are predominantly nonionic. This fits the idea that nonionic substances can raise TDS without contributing much to conductivity.