some chem questions!!!!!!!!!!!!!!

Question

1.點解sodium carbonate會係alkaline?
佢同acid反應唔係會有carbon dioxide出現架咩?

2.點先叫efferressence occurs?why有hydrogen only叫gas bubble
有carbon dioxide叫efferressence occurs?

3.calcium hydroxide係slightly soluble in water,咁叫係alkaline呀?

4.點解chem書成日都話pipette係25cm^3?

5.點解呢dilute acid，即係加左水係d acid到，點解the no.of mole of the solute會一樣呀?
點解唔會多左呢?因為多左水既molecules呀嘛?why??

Answer 1

1.
Sodium carbonate is an alkali because carbonate ion can hydrolyzed in water to give OH-(aq) ion.
CO32-(aq) + H2O(l) = HCO3-(aq) + OH-(aq)
An alkali is a substance which can be dissociated in water to give OH-(aq) ion. Therefore, sodium carbonate is an alkali, and its solution is alkaline.

2.
Effervescence means the phenomenon that gas bubbles are formed. The bubbles can be hydrogen, carbon dioxide, or any gas else.

3.
Calcium hydroxide dissociates in water to give calcium ion and hydroxide ion.
Ca(OH)2(s) + aq → Ca2+(aq) + 2OH-(aq)
An alkali is a substance which can be dissociated in water to give OH-(aq) ion. Therefore, calcium hydroxide is an alkali, no matter whether how low the solubility is.

4.
Pipettes have different capacities. The commonest capacity is 25 cm3.

5.
In dilute acid, the acid is the solute, and water is the solvent.
When water is added to the dilute acid, the amount of the solvent (water) is increased, but the amount of the solute (acid) is unchanged.