90 days

By this time, almost every topic for the various subjects have been covered.

So, let's ramp up our revision schedules!

This week:

CHEM, Mnemonics, and that QA test.

1. Reactivity series.

I got this from some people from 4SB, and it seems to help me. So, for those who have problems memorising, hope this can help.

Please Santa Claus Help Make A Zebra's Itchy Leg Heal Completely Soon.

Please [Potassium]

Santa [Sodium]

Claus [Calcium

Make [Magnesium]

A [Aluminum]

Zebra's [Zinc]

Itchy [Iron]

Leg [Lead]

Heal [Hydrogen]

Completely [Copper]

Soon [Silver. And Silver is cheaper than Gold, Gold cheaper than Platinum]

If you are used to a certain method of memorising, you may want to add other non-metallic elements in, specifically CARBON and HYDROGEN.

Carbon fits in between Aluminum and Zinc, because the oxides of everything from Zinc and below CAN be reduced by carbon. Everything above requires electrolysis.

2. Rate of Reaction.

Ok, this is my personal way of memorising the difference between exothermic and endothermic reactions. Correct me if I am wrong.

BAN MRX

BAN:

Breaking of bond=

Absorbing energy=

eNdothermic reaction

MRX:

Making bond=

Release of energy=

eXothermic

3. Anion & Cation Test.

i)Anion [non-metal ions]

1. Add Nitric Acid

Effervescence: Carbonate.

2. Split Solution into 2 test tubes. Add Ba(NO3)2 to one, AgNO3 to the other.

Ba(NO3)2: Sulphate.

AgNO3: Chloride {if white}, Iodide {if yellow}.

3. If all else fails, get a new solution, add NaOH, aluminum foil, warm gently. Test with a damp red BLUE litmus.

Effervescence, Litmus turns red: Nitrate.

ii)Cations [metal ions]

For NaOH

-Only NH4 has no ppt.

-Only Al, Pb, and Zn dissolve in excess [The amphoteric metals]. Read on to differentiate.

For Aq. Ammonia

-Only Ca has no ppt. [Ammonia is redundant]

-Only Cu2+ and Zn are soluble in excess.

Differentiating the Amphoteric metals.

-Add HCl to excess. PbCl2 is insoluble. Hence, Pb is identified.

-Add aq. Ammonia to excess. Aluminum Nitrate is insoluble in excess. Hence, Al is identified. Leaving the last solution to be Zn.

4. Formulas for stoichio.

n=m/Ar

n=m/Mr

n=V/24dm cube

n=V/24000cm cube

n=MV [concentration * volume]

Hence, M1V1 = M2V2

Then, there's the yield, emp. formula vs molecular formula.

All the best for chem test!