chemistry calculations -try them out! Good luck!

For those of you who are sitting for chemistry SPM this year, Here are some examples of important calculations in chemistry SPM. Try them out, and get the answers from me on this Friday, insyaAllah!

Chemistry calculations ( show clear workings)

name ………………………………………………….class…………………….Teacher……………………………………..…

1)      a) The mass of two atoms of element Y is equal to that of three atoms of oxygen. What is the relative atomic mass of element Y? [ RAM: O,16]  ……………………………………………….

b) What is the relative molecular mass of sodium thiosulphate? [ RAM : Na, 23,S,32, O,16]

……………………………

c) A sample of aluminium oxide contains 1.08g aluminium and 0.96 g of oxygen. What is the empirical formula of the compound? [RAM: O,16, Al,27] …………………………………….

d) The empirical formula of a compound is CH₂. Its relative molecular mass is 42. Find its molecular formula. [relative atomic mass : H,1: C,12] ………………………………………..

e) Find the empirical formula of a compound that consists of 32.4% of sodium, 22.6% of sulphur and 45% of oxygen. [given RAM of Na,23 S, 32 O,16] ……………………………………………..

f)refer to diagram 1

Mass of crucible + lid                                     = 38.50 g

Mass of crucible + lid     + magnesium ribbon     = 39.22 g

Mass of crucible + lid     + magnesium oxide        = 39.70 g

[ given RAM Mg: 24. O; 16]

Calculate

i)                    mole of magnesium…………………………

ii)                  mole of oxygen…………………………

iii)                the empirical formula of magnesium oxide ……………………

g)  Refer to diagram 2

Mass of combustion tube                                            = 38.0 g

Mass of combustion tube            + copper oxide  = 46.0 g

Mass of combustion tube            + copper              = 44.4 g

Calculate

iv)                mole of copper………………………………….

v)                  mole of oxygen…………………………….

vi)                the empirical formula of copper oxide ……………………

2)      a) Question below use equation 

4CuO  +  CH₄  à 4Cu  + CO₂  + 2H₂O

16g of copper(II) oxide, CuO is reacted with excess methane, CH₄. Using the equation above, find  

  i) the mass of copper that is produced………………………………..

ii) Volume of carbon dioxide that can be collected at room conditions [ 1 mol of gas occupy 24 dm³ at room conditions]

………………………………………………………

iii) Number of moles of water formed …………………………………………………

iv) Number of molecules of water formed [ N_A= 6.02 x 10 ²³ particles/mol] …………………………

3)      a) What is the concentration of a solution in grams dm^-3 when 36.5 g of hydrogen chloride, HCl is dissolved in water to make up 500 cm³ of solution?

……………………………………….

b) The molarity of a bottle of nitric acid , HNO₃ solution is 2.0 mol dm^-3 . What is the concentration of the solution in g dm^-3? [RAM : H,1: N,14,O,16]

…………………………………..

c) Find the volume of 2.0 moldm^-3 sulphuric acid , H₂SO₄, needed to prepare 100 cm³ of 1.0 mol dm_-3 sulphuric acid? ……………………………………………………

d) 25 cm³ potassium hydroxide solution is neutralized by 0.15 moldm^-3 sulphuric acid 30.5 cm³. What is the molarity of potassium hydroxide solution? ………………………………………………

4)      CALCULATE THE RATE OF REACTION:

refer to diagram 3

a)      Calculate the overall rate of reaction for this experiment……………………………..

b)      Calculate the rate of reaction in the first 2 minutes ……………………………………..

c)       Calculate the rate of reaction at 3^rd minute …………………………………….

5)      THERMOCHEMISTRY.

a)      100 cm³ of 1.0 mol dm^-3 lead(II) nitrate solution was mixed with 100 cm³ of 1.0 mol dm^-3

potassium sulphate solution . Temperature increase from 27 ^oC to 32 ^oC.

i)                    Calculate the heat change ………………………………….

ii)                  What is the name of this reaction? ……………………………………….

iii)                Calculate the heat of reaction……………………………….

iv)                The experiment is repeated using double the concentration of both solutions. Predict the temperature increase …………………………………….

b)      Excess zinc powder 5 g is added to 100 cm³ of 0.5  mol dm^-3 iron(II) sulphate  solution . Temperature increase is 9.6 ^oC.

i)                                Calculate the heat released during the experiment. ………………………………………….

ii)                              What is the name of this reaction? ……………………………

III)                            Calculate the heat of reaction………………………………………………

IV)                           Iron(II) sulphate is replaced by iron(II) chloride solution, with all other conditions remain the same.  What is the effect on the heat change? Explain your answer

…………………………………………………………………………………………………………………….

V)                             Excess zinc powder  is replaced by excess magnesium powder, with all other conditions remain the same.  What is the effect on the heat change? Explain your answer

c)       200 cm³ of 2.0 mol dm^-3 sodium hydroxide  solution was mixed with a fixed volume

of 1.0 mol dm^-3 of H₂SO₄ . Given Δ H = - 57.3 kJ /mol

i)                                Calculate the heat given off during experiment ……………………………..

ii)                              Calculate the volume of acid sulphuric acid used…………………………………

iii)                            If the experiment is repeated with ethanoic acid , all other conditions remain the same, is the heat change be the same? Explain your answer

……………………………………………………………………………………………………………………………

d)      1.6 gram methanol, CH₃OH is burnt completely in excess oxygen, O₂. The heat given off is used to heat 300 cm³ of water. Temperature increase by 28.8 ^o C. 

i)           Calculate the heat change………………………………

ii)         Calculate the heat of combustion……………………………………….

iii)       The heat of combustion is greater with ethanol than in methanol. Explain

……………………………………………………………………………………………………………….

End of calculations, Best of luck from us teachers!!