JAMB - Chemistry (1991 - No. 17)
A sample of temporary hard water can be prepared in the laboratory by?
disolving calcium chloride in distilled water
saturating lime water with carbon (IV) oxide
saturating distilled water with calcium hydroxide
dissolving sodium hydrogen trioxocarbonate (IV) in some distilled water
Forklaring
A sample of temporary hard water can be prepared in the laboratory by saturating lime water with carbon (IV) oxide. This means passing CO\(_2\) in excess through lime water, Ca(OH)\(_2\) to first obtain CaCO\(_3\), which later changes to soluble calcium hydrogentrioxocarbonate (IV) by passing more CO\(_2\) which imparts temporary hardness to water.
Ca(OH)\(_2\) + CO\(_2\) → CaCO\(_3\) + H\(_2\)O
CaCO\(_3\) + CO\(_2\) + H\(_2\)O → Ca(HCO\(_3\))\(_2\)