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The following data were obtained when dinitrogen and dioxygen react together to form different compounds:
Mass of dinitrogen               Mass of dioxygen
(i) 14g                                              16g
(ii) 14g                                             32g
(iii) 28g                                            32g
(iv) 28g                                            80g
which law of chemical combination is obeyed by the above experimental data? Give its statement?


By fixing the mass of dinitrogen as 28g, we can calculate the masses of dioxygen that will combine with 28g of dinitrogn.   
  These are in the ratio of 32 : 64 : 32 : 80 i.e. 1:2:1:5 which is simple whole number ratio. Hence the given data obeys the law of multiple proportions. For definition refer to the answer of question 40.
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What is the concentration of sugar (C12H22O22) in mol L–1 if its 20g are dissolved in enough water to make a final volume up to 2L? 

Molar mass of sugar 

                 
Number of moles of sugar = ><br>                                      = 0.0585 mol<br><br><img class=  Molar concentration (molarity)
                       

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Pressure is determined as force per unit area of the surface. The SI unit of pressure, pascal is as shown below:
1 Pa = 1N m–2
If mass of air at sea level is 1034 g cm–2, calculate the pressure in pascal.


Pressure is the force (i.e. wt.) acting per unit area.
But weight  = mg

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If the density of methanol is 0·793 kg L–1, what is its volume needed for making 2·5L of its 0·25 M solution?

Molar mass of methanol (CH3OH)
                = 12 + 4 x 1 + 16 = 32g mol-1
                = 0.032 kg mol-1
       Molarity of the given solution
       
Applying the molarity equation,

(Given solution) 



or     

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Match the following prefixes with their multiples:

A. micro (i) 106
B. deca (ii) 109
C. mega (iii) 10–6
D. mega (iv) 10–15
E. femto (v) 10

A.

micro

(i)

10–6

B.

deca

(ii)

10

C.

mega

(iii)

106

D.

mega

(iv)

109

E.

femto

(v)

10–15
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