Student Cmn Mistakes

LSS Chemistry Secondary Two

Students’ Common Record Sheet

Student’s Common Mistakes Topic(s): Chemical Formulae & Solubility 1.

Students tend to write the chemical formulae for the following compound wrongly: Chemical Name Sodium Chloride

Na(Cl)

NaCl

Barium Sulfate

Ba(SO4)

BaSO4

Ba2(SO4)2 Sodium Hydroxide

Na(OH)

NaOH

* Bracket only to be used for two or more compounds. e.g. Fe(OH)2 2.

When asked to list the soluble/insoluble substance from a given chemical equation students, tend to write water as a soluble substance. Please note that water is not the accepted answer. Example: Iron(II) Hydroxide + Hydrochloric acid  Iron Chloride + Water Soluble substance(s) : Hydrochloric acid, Iron chloride and Water. Insoluble substance(s) : Iron (II) hydroxide Please do not write water as the soluble substance

Ms Ricca Jasin 10/9/2009

Nil Sine Labore

Victoria School

LSS Chemistry Secondary Two

Students’ Common Record Sheet

3. Confusion of the formulae for nitrate, nitrite, nitride

phosphate, phosphite, phosphide sulfate, sulfite, sulfide Nitrate Nitrite Nitride

NO3NO2N3-

Sulfate Sulfite Sulfide

SO42SO32S2-

Phosphate Phosphite Phosphide

PO43PO33P3-

Tips to remember … All negative ions (anions) end in “-ide”, “-ate”, or “-ite”

“-ates” These contain several oxygen atoms. There is no rule about how many oxygen atom they consist (you just have to memorize them)

“-ites” Negative ions that end in “-ites” contain one less oxygen than the “-ates” and they have same charge as the the “-ates”

“-ides” These are single atom ( except for OH- and cyanide CN- ) You can tell the charge from the position on the periodic table Example: Family VII ( F,Cl, Br, I) all form 1- ions Family VI ( O, S ) all form 2- ions Family V ( N, P ) all forms 3- ions

Hope the above tips useful for u… All the best for SA2! Ms Ricca Jasin 10/9/2009

Nil Sine Labore

Victoria School