Laboratory 8: Determine Water Hardness

Titration Moles

Moles of A= Concentration of A x Volume of A example if A= EDTA solution the mole of EDTA solution is Concentration x Volume Moles of B= Concentration of B x Volume of B example if B is water

Analyte

Substance being analyzed (in our case Ca and Mg)

Endpoint

The change of color

How to determine hardness range of water?

Titrating the sample with a compound called EDTA Titrating: adding a carefully measured volume of a solution with known concentration (the titrant) to a solution with an unknown concentration (the analyte) until a chemical reaction is complete.

What is hard water?

Water containing significant amounts of calcium ion (Ca2+) and magnesium ion (Mg2+)

Simplified Understanding of how Titration determines water hardness using EDTA

Water hardness is caused by minerals like calcium and magnesium. To find out how hard the water is, you can use a chemical called EDTA. Imagine you have a jug of water, and you want to know how much calcium and magnesium are in it. You add a few drops of EDTA to the water. The EDTA grabs onto the calcium and magnesium ions in the water. As you keep adding EDTA, it keeps grabbing onto these minerals until they're all locked up. You can tell this is happening when the water changes color. By measuring how much EDTA you added, you can figure out how much calcium and magnesium were in the water. The more EDTA you used, the harder the water is because it had more calcium and magnesium. So, in simple terms, titration with EDTA helps us "trap" the minerals in the water and count how many there are, which tells us how hard the water is.

Titration

a chemical qualitative analysis technique commonly used to determine the concentration of a given analyte in a mixture

Concentration

if a bottle is 5% NaCl then there are 5 grams of NaCl per 100mL of water mass of substance in grams -------------- volume of solution (100mL)

Why is an indicator used in a titration?

it is used to provide a visual indication for the end point (change of color)

EBT turns ____ when it forms a complex with Ca or Mg

red

Equivalence point

the point in the traction process at which equal quantities of two reactants are mixed At the Equivalent point Moles of A (in this case EDTA solution) = moles of B (water) Concentration A x Volume A= Concentration B x Volume B

Chelator

the term means "claw" and the EDTA uses its chemical components to grab onto the Ca2+ like a claw

What does hardness in water do?

- calcium and magnesium ions react with soap to form insoluble solids that form scum that sticks to sinks and bathtubs and also make the soap lose its cleaning power

Water Hardness range (in terms of ppm of CA2+ and Mg2+)

0-17 ppm : soft 17-60 ppm: slightly hard water 60-120 ppm: Moderately hard water 120-180 ppm: Hard water Over 180: very hard water

1% solution

1g/100mL

1ppm

1mg/L

Percentages of Fresh Water

69% is from ice and glaciers 30% is groundwater 1% is surface water

Where is the world's water?

97% is in oceans (salt water) 3% is fresh water (in basins, underground, rivers, etc)

Concentration of B (water) = ?

Cb = (Ca x Va )/ Vb

How to determine hardness range of water... continued?

EDTA reacts with calcium and magnesium ions in a 1:1 ratio called "chelator"

EBT

Eriochrome Black T (the indicator)

results of titration explained

If there is a change of color once EDTA is added to the solution in just a drop, then there is a high level of Ca and Mg If more EDTA is needed then the concentration of Ca and Mg is lower