water Flashcards
what is a useful property of soft water?
it readily forms a lather with soap
what is a not useful property of hard water?
hard water reacts with soap to form scum therefore more soap is needed to form a lather calcium ions (from hard water) + stearate ions (from soap) --> scum (calcium stearate) which is insoluble
what products do not produce scum? and why?
soapless detergents because they do not contain soap and soap is what helps produce a lather as soap contains stearate ions
what does hard water usually contain?
hard water contains dissolved compounds usually calcium or magnesium
when do these compounds dissolve into the water?
when the water comes into contact with rocks i.e. flows over rocks calcium and magnesium dissolve into the water
how many types of hard water are there?
two types:
- permanent hard water
- temporary hard water
what is the difference between Permanent and temporary hard water?
- permanent hard water remains when hard when boiled
- temporary hard water softens when boiled
what do temporary hard waters contain?
hydrogencarbonate ions HCO3-
what do these hydrogencarbonate ions do when heated?
the hydrogencarbonate ions decompose on heating into carbonate ions which react with the calcium and magnesium ions (in the hard water) to from precipitates
what is the affect of the calcium/magnesium precipitates?
all the calcium and magnesium ion are precipitated out as calcium carbonate and magnesium carbonate which are insoluble therefore the water is soft once more
how can using hard water increase costs?
- more soap is needed (to form a lather)
- when temporary hard water is heated it can produce limescale this reduces the efficiency of heating systems and kettles
calcium hydrogencarbonate –> calcium carbonate + carbon dioxide + water
what are some benefits of hard water?
hard water contains calcium compounds which are good for the health e.g. development and maintenance of bones and teeth
also helps reduce heart disease
how can both types of hard waters be made soft?
by removing the dissolved calcium and magnesium ions
how can the calcium and magnesium ions be removed?
the calcium and magnesium ions can be removed by adding sodium carbonate which reacts with calcium and magnesium to form insoluble precipitates of calcium carbonate and magnesium carbonate
the calcium and magnesium are no longer dissolved in the water therefore can’t make it hard
what is the benefit of sodium carbonate?
sodium carbonate + calcium –> calcium carbonate + sodium
- it does not react with soap to form scum and it doesn’t form limescale deposits
- it is readily available and can take the form of bath salts or washing soda
what are the disadvantges of sodium carbonate?
- it does not soften water used in water pipes or central heating systems which can be totally ruined by limescale
what is the more commercial way of softening water?
- commercial water softeners e.g. ion exchange columns
how do these ion exchange columns work?
the columns contain hydrogen and sodium ions
these hydrogen and sodium ions replace the calcium and magnesium ions when the hard water passes through the column
dishwashers have built in systems like this
what is the disadvantage of an ion exchange column?
the softened water contains sodium which is bad for your health as it can lead to high blood pressure and heart problems
what is essential to human life?
the correct water quality
what kind of water should humans drink?
water which has sufficiently low levels of dissolved salts and microorganisms
what do filters contain?
water filters contain carbon, silver and ion exchange resins
what do these filters do?
these filters contain carbon, silver and (ion exchange resins) remove some dissolved substances from water improving the taste and quality
why is chlorine added to water?
to kill and reduce the amount of microorganisms
