Question

How do you estimate what concentrations of ZnCl₂ will give a conductivity range of 300-2000 microseconds/cm?

If posible please explain how in detail.

Answer 1

Electrical Conductivity is the ability of a solution to transfer (conduct) electric current. It is the reciprocal of electrical resistivity (ohms). Therefore conductivity is used to measure the concentration of dissolved solids which have been ionized in a polar solution such as water. The unit of measurement commonly used is one millionth of a Siemen per centimeter (micro-Siemens per centimeter or µS/cm). When measuring more concentrated solutions, the units are expressed as milli-Siemens/cm (mS/cm) i.e.- 10-3 S-cm (thousandths of a Siemen). For ease of expression, 1000 µS/cm are equal to 1 mS/cm. Often times conductivity is simply expressed as either micro or milli Siemens. However this unit of measurement is sometimes (incorrectly) referred to as micro-mho's rather than micro-Siemens. The expression "mho" was simply the word ohm spelled backwards. Several means of conductivity expression have been adopted by various industries as a way of making the units of expression into whole numbers. The water softening industry refers to "grains" of hardness and uses TDS or total dissolved solids as a measurement scale. While TDS is really a gravimetric measurement, because in solution the solids are predominately present in ionic form, they can be approximated with conductivity. The TDS scale uses 2 µS/cm = 1 ppm (part per million as CaCO3). It is also expressed as 1 mg/l TDS. While the method of measurement is the same, some conductivity meters can make the conversion and express the results of a measurement in many different units.  This is helpful for users who are accustomed to one particular unit of measurement.

The electrical conductivity of aqueous solutions is governed by the presence and concentration of ions in solution. Therefore, pure water does not conduct an electrical current well sine the concentrations of hydrogen and hydroxide ions are very small. Solutes whose solutions are conductive are called electrolytes -- a solute is considered a strong electrolyte if it dissociates completely into its constituent ions.

Ex. strong electrolytes --> ionic compounds like NaCl and KI
compounds with highly polar covalent bonds --> HCl in water

Thus, if concentration was higher, that means more ions are present per liter of water -- more ions = more conductivity.