1. Conductivity

2. 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)

3. 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

4. Conductivity meter

5. Hardness

6. 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++2HCO CaCO3 +CO2+H2O
Heat

7. 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 mg/L.

8. 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
Considerable scale buildup and staining
Generally softened if >200 mg/L
Very hard
>200
Requires softening for household or commercial use

9. Scale in a pipe

10. Scale in Boiler

11. Corrosion

12. 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++

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

14. 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 SO 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

15. 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.

16. Na2CO3 (Soda ash)

17. 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-