Acid and alkalis

Question 1

What is the most common way of removing dangerous metal ions from water and how is it achieved

Answer 1

precipitate them as metal hydroxides. This is achieved by adding alkaline materials which increases OH- concentration. This causes the toxic metal ions to precipitate back into metal hydroxides due to Le Chateliers principle
MOH <-> M+ + OH-

Question 2

Why is the most common way of removing dangerous metal ions from water effective

Answer 2

The dangerous metal hydroxides have low solubility

Question 3

what is alkalinity

Answer 3

the ability for water to neutralise acid. High alkalinity doesn’t always mean high pH, just like buffer solutions

Question 4

What is water hardness and why does it mean harder water requires more soap

Answer 4

The amount of Calcium, magnesium (mainly), manganate and iron ions. Soap (sodium stearate), which is a compound of sodium and long chain carboxylic acids, reacts with calcium and magnesium to form calcium stearates and magnesium stearates which are insoluble.

Question 5

define exergonic and endergonic

Answer 5

exergonic - energy is released and reaction is spontaneous (gibbs free energy change is negative)
endergonic - energy is consumed, reaction is not spontaneous (gibbs free energy change is positive)