Summary Chemistry AS Level OCR

Chem

YEAR 1

, xH20 calculations

Example

13.52g of Mgso4.Xh20 is heated to remove all water

6.6 of mgs04 remains calculate x

6.6 divided by mr of mgso4 = 0.0548

13.52-6.6=6.92 divide mr of h20= 0.3844 0.0548:0.3844

0.3844 divide 0.0548=7

x=7

, Limiting reagent
Example

H2so4 +2Naoh -----> na2so4 + 2H20

25cm of 1moldm-3 of h2s04

1.5g of naoh

Moles of h2so4= 25 times 1 divide by 1000= 0.025

Moles of naoh= 0.0375

0.025 needs 0.05 moles of naoh because its a 1:2

Hence naoh is limiting reagent as theres only 0.0375 moles

, Ideal gas equation
Rmrbr pv=nrt where p=pascal v=volume n=mole r=8.31 t=temp in Kelvin
Example
cac03-------> cao + co2
Calculate mass in kg of calcium carbonate that produce 998.9dm3 of co2 at 840c and 100kpa
Conversions 840c+273=1113k 100kpa=100000pa and 998.9dm3=0.9980
Moles of co2 = pv divide by rt = 100,000 times 0.9989 divide by 1113 times 8.31
= 10.8 moles 1:1 so mr of caco3=100 times by 10.8=1080 grams divide by 1000 to get kg =
1.08kg
Conversions for standard room temp
1kpa=1pa make sure pressure is always in pascal
1m3= 1,000,000 cm3 make sure volume always in metre cubed
0c=273k make sure temp is always in Kelvin for room temp its 298 which is the only diff