Conductivity

Conductivity Is a measure of the ability of that solution to conduct an electrical current. Because the electrical current is transported by the ions in solution, the conductivity increases as the concentration of ions increases. Electrical conductance is reported in units of microsiemens per centimeter (µs/cm)

Conductivity The conductivity of a sample can also be employed to estimate the ionic strength of a solution (a measure of the concentration of ions in that solution). The ionic strength=(1.6*10-5)*Conductivity

Conductivity meter

Hardness

Hardness Carbonate hardness associated with HCO3-, CO32- Non carbonate hardness associated with other anions, particularly, Cl-, SO42- Because HCO3- dissociates at high temperature, a result of heating hard water is scale formation due to CaCO3 precipitation Ca2++2HCO3- CaCO3 +CO2+H2O Heat

Hardness As with alkalinity, hardness is usually expressed as an equivalent concentration of CaCO3. However, hardness is a property of cations (Ca2+, Mg2+) while, alkalinity is a property of anions (HCO3-, CO32-). An ideal quality goal of total hardness is about 70-90 mg/L.

Degree of Hardness Soft <75 Moderately hard 75-120 Hard 120-200 mg/L CaCO3 Effects Soft <75 May increase toxicity to fish of dissolved metals May increase corrosivity of water to metals No scale deposits Efficient use of soap Moderately hard 75-120 Not objectionable for most purposes Required somewhat more soap for cleaning Above 100 mg/L may deposit significant scale in boilers Hard 120-200 Considerable scale buildup and staining Generally softened if >200 mg/L Very hard >200 Requires softening for household or commercial use

Scale in a pipe

Scale in Boiler

Corrosion

Calculation of Hardness in mg/L as CaCO3 M++ in mg/L * 50 Equivalent weight M++ Total hardness (mg/L as CaCO3) is the summation of all M++

Equivalent weight Molecular or atomic weight Magnitude of ionic charge or oxidation number

Group work: Hardness Calculate hardness in mg/L as CaCO3 of the following water results Na+ 20 mg/L Cl- 40 mg/L Ca2+ 15 mg/L SO42- 16 mg/L Mg2+ 10 mg/L NO3- 1 mg/L Sr2+ 2 mg/L Atomic mass: Na=23, Ca=40, Mg=24.4, Sr=87.6, Cl=35.45, S=32, O=16, N=14

Slaked Lime Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca(OH)2. It is a colorless crystal or white powder and is obtained when calcium oxide (called lime or quicklime) is mixed, or "slaked" with water.

Na2CO3 (Soda ash)

Group work: Determination of Hardness Two water samples were analyzed for soluble constituents. Partial results of the analysis are given below. Determine in g/m3 as CaCO3 of (1) Total hardness (TH), (2) Carbonate hardness (CH), and (3) Non-carbonate hardness (NCH) of each sample. (Atomic mass; Ca=40, C=12, O=16) Constituent Concentration, eq/m3 Sample 1 Sample 2 Ca2+ 5 2 Mg2+ 1 4 HCO3- 3 7 Cl-