Friday, August 26, 2011

Determine specific heat in J/g times degree celcius . Mass of substance 29.2g, initial temp 34.4degrees celcius, final temp 68.1degrees celcius, heat applied 436.9 j, what is the formula of hear capacity ?

Q- 1 What is the heat capacity ?
Answer :- Amount of heat which required to raise the temperature of one gram substance by one degree Centigrade is called  heat capacity of that substance.

example:-
heat capacity of water is 4.18 j /gC  
That means one gram of water require heat 4.18 j  to raise the temperature of water by one degree centigrade.


 Q-2  Determine specific heat in J/g times degree celcius . Mass of substance 29.2g, initial temp 34.4degrees celcius, final temp 68.1degrees celcius, heat applied 436.9 j, what is the formula of hear capacity ?
 Answer
Formula for the heat Q = M*C*delta T
                  M = mass of the substance in gram
                  C = specific hear capacity of substance
          delta T = final temperature  - initial temperature

from the problem
           delta T = 68.1 - 34.4
                      =33.7 C

         Mass M = 29.2 gram
         Heat Q  = 436.9j

plug the value in above formula we get
                    Q = M*C*delta T
            436.9 j = 29.2 gram * C* 33.7degree Celsius
              436.9 = 984.04gram degree celcius *  C

divide by 984.04gram degree Celsius we get
                 
 0.44 j / gram degree celcius = C (specific heat capacity )

 Answer heat capacity = 0.44 j/g K  or 0.44j/gC
heat capacity of water
heat capacity of water

density of table salt is 2.16g/cm^3. What is volume in Liters of a 154.3kg salt sample

density of table salt
density of table salt

Answer :-

   step - 1
             convert mass in grams 
                  1 kg = 1000  gram
          so 
            154.3kg  = 154000 gram 
   Step - 2 
             volume = mass /density 
                         =  154300 gram / 2.16 (g/cm^3) 
                         = 71435 cm^3 
   Step - 3
        1000 cm^3 = 1 liter 
       so
     71435 cm^3  = 71435/1000 liter 
                          = 71.44 liter
          Answer  = 71.44 liter

Monday, July 11, 2011

Balance the ionic equation by half reaction method O3+ Br- -------> O2 + BrO-



Answer:-

Step -1  
       Find the oxidation number of Br in BrO-
       in combination state oxygen has oxidation number = - 2 
             Br + O = - 1 
               Br -2 = -1 
                   Br = +1  

Step -2 
        write oxidation half reaction 

               Br-  <-----------> BrO- 
               -1                       +1
       here oxidation number of Br is increasing by 2 
       so add 2 electron to balance it 

       we get 
              Br-  <-----------> BrO-   + 2e-             
Step -3 

add OH - ions to balance the charge reaction 

Br- +  2OH-   <----------->BrO-   + 2e
Step - 4 
add H2O to balance the hydrogen and oxygen 

Br- +  2OH-   <----------->BrO-   +H2O +  2e 

balanced oxidation half reaction

 Br- +  2OH-   <----------->BrO-   +H2O +  2e   ---------------(1)

similarly you can get balanced half reduction reaction 

Balanced reaction half reaction 
O3 + H2O + 2 e- <-----------> O2 + 2 OH-        ---------------(2)

add both equations we get 


Br- +  2OH-  + O3 + H2O + 2 e- <-----------> BrO-   + 2e + O2 + 2 OH-
simplify the equation we get

O3+  Br- <----------->O2 +  BrO-

Answer : -  Equation was already balanced 



Balance the ionic equation
Balance the ionic equation



Sunday, July 10, 2011

how many grams are in 1.8 x 10^23 atoms of silver


number of moles of silver = number of atoms / Avogadro number 
                                       = 1.8x10^23 atom/ 6.022x10^23 per moles
                                       =0.2989 moles 
mass in grams of silver    = number of moles * molar mass of substance 
                                       = 0.2989 moles * 107.87 gram /moles 

                                       = 32.34 grams 
Answer = 32.34 grams 
how many grams are in  atoms of
how many grams are in 1.8 x 10^23 atoms of silver

What is the molarity of pure water at 20 C?density table of water

 molarity of pure water
 molarity of pure water


   density of water is at 20 C = 0.9982071 gram /ml
let we take 1 liter water 
                                   1 liter = 1000 ml 
            mass of 1 liter water = volume *density  
                                             = 1000 ml * 0.9982071 gram /ml 
                                             =  998.2071 gram

  molar mass of water  H2O = 2* 1.008 + 15.999
                                             = 18.015 gram / moles

number of moles of water in one liter 
                                            = mass of substance / molar mass
                                            = 998.2071 gram/18.015 (gram / moles)
                                            =55.41 moles 

        molarity of water        = number of moles of water / volume of water 
                                           = 55.41 moles/ 1liter 
                                           = 55.41moles/liter
Answer:-  molarity of water at 20 C is 55.41M