Water Flashcards
Hard water
Containing Ca2+ and Mg2+ ions.
Why does temporary hard water soften when boiled?
Contains hydrogencarbonate ions (HCO3-)
Decomposes on heating to produce carbonate ions (CO3 2-)
reacts with calcium and magnesium ions to form precipitates (CaCO3) (MgCO3)
Write the balanced equation for the reaction which forms lime scale in a kettle
Ca(HCO3)2 –> CaCO3 + H2O + CO2
The reaction between lime scale and ethanoic acid when you use vinegar to remove the lime scale from your kettle.
CaCO3 + 2CH3COOH –> (CH3COOH)2Ca + H2O + CO2
Describe the steps in the process of treating water to make it safe to drink.
1) The water is collected and stored in a reservoir
2) Whilst in the reservoir large particles of mud can settle to the bottom
3) Smaller, solid particles are removed by filtering the water.
4) Chlorine is added to reduce the number of microbes
5) The water is then stored ready for use.
How does sodium carbonate make hard water soft? (Na2CO3)
The Na+ replace Ca2+ and Mg2+ in the water
Insoluble calcium and magnesium carbonate formed
CaCO3 (s) + MgCO3 (s) formed
How can you make hard water soft with a commercial water softener such as ion exchange column?
Hydrogen ions (H+) or sodium ions (Na+) Replaces Ca2+ and Mg2+ when hard water passes through the column.
What are the advantages of hard water?
taste better
helps to develop / maintain bones
helps to develop / maintain teeth
reduces heart disease
What are the disadvantages of hard water?
Increase costs because more soap is needed.
Temporary hard water heated
Scale produced –> reduces the efficiency of heating systems and kettles
Difference between hard and soft water when reacting with soap
Soft: forms lather
Hard: reacts with soap to form scum –> more soap needed to form lather
What is special about soapless detergents?
Do not form scum
Two types of hard water and difference when they are boiled
Permanent - remains hard when boiled
Temporary - softens when boiled
What is water of the correct quality like?
Have sufficiently low levels of dissolved salts and microbes
How is water of the correct quality produced?
Choosing appropriate source
Passing water through fitter beds to remove any solids
Sterilize with chlorine
What does water filters contain?
Carbon and silver
