0.500 g of a sample which contains copper is analyzed iodometrically. Copper (II) is reduced to copper (I) by the iodide. What is the percent copper in the sample if 20.00 cm3 of 0.1 M sodium thiosulphate solution is required for the titration of the liberated iodine?

                      %Copper  =  25.42 %

Explanation:

                    For solving this problem one first write down the half reactions as;

Reduction of Cu²⁺ to Cu⁺¹ by I⁻:

                                2 Cu²⁺  +  4 I⁻   →   2 CuI  +  I₂

Secondly, the titration reaction between Na₂S₂O₃ with I₂ as;

                             2 S₂O₃²⁻  +  I₂   →   S₄O₆²⁻  +  2 I⁻

Now, Calculate Moles of S₂O₃²⁻ as;

                             Moles  =  Molarity × Volume

Putting values,

                             Moles  =  0.1 mol/L × 0.02 L

                             Moles  =  0.002 moles of S₂O₃²⁻

From first two equations we can conclude that,

2 moles of S₂O₃²⁻ liberated I₂ produced by  =  2 moles of Cu²⁺

So,

0.002 moles of S₂O₃²⁻ will liberate I₂ produced by  = X moles of Cu₂⁺

Solving for X,

                       X =  0.002 mol × 2 mol / 2 mol

                       X  =  0.002 mol of Cu²⁺

So, we require 0.002 moles of Cu²⁺ to produce I₂ enough for titrating with 0.1 M (20.00 mL) sodium thiosulphate solution.

Now, Calculate mass of Copper as,

                       Mass  =  Moles  ×  A.Mass

                       Mass  =  0.002 mol × 63.55 g/mol

                       Mass  =  0.1271 g of Copper

Lastly, calculate % copper as,

                       %Copper  =  0.1271 g / 0.500 g × 100

                       %Copper  =  25.42 %

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.

the answer is yes

it has kinetic energy

reason

an object has kinetic energy when you stop the force carrying it, the object will stay in motion.

hope this contact me for more questions if you'd like: )