Question
Question: Silver metal in ore is dissolved by potassium cyanide solution in the presence of air by the reactio...
Silver metal in ore is dissolved by potassium cyanide solution in the presence of air by the reaction:
4Ag+8KCN+O2+2H2O→4K[Ag(CN)2]+4KOH
Which of the following is true regarding the above reaction?
(A) The amount of KCN required to dissolve 100g of pure Ag is 120g
(B) The amount of oxygen used in this process is 7.40g (for 100gm pure Ag )
(C) The volume of oxygen used at S.T.P is 5.20 litres for the same process
(D) All of the above
Solution
The number of molecules that take part in the reaction is the stoichiometric coefficient or stoichiometric number. You will notice that there are an equal number of elements on both sides of the equation when you look at any balanced reaction. Basically, the stoichiometric coefficient is the number that is present before atoms, molecules, or ions. We can use these to also find the mass of a product formed when mass of reactants are given.
Complete Step-by-Step solution
Let us first write the equation that is provided in the question
4Ag+8KCN+O2+2H2O→4K[Ag(CN)2]+4KOH
Now, we can say that
4nAg=8nKCN=1nO2
Where
n is the number of moles
And the numbers are the stoichiometric coefficients of the reactants of the chemical equation
Now, let us take a look at each of the options provided
The weight of Ag is given as 100g
The amount of KCN required is given as 120g
Now, let us check the validity of the option (A).
4nAg=8nKCN
Let the assumed mass of KCN be m
Then,
4(108100)=8(65m)
Upon solving, we get
m=120.3g≈120g
So, option (A.) is correct
Similarly,
For option (B.),
Let us assume the mass of O2 as mO2
Then,
4nAg=1nO2
Upon substituting values, we get
4(108100)=1(32mO2)
On further solving, we get
mO2=7.40g
So, option (B.) is also correct
Now, we will verify option (C.)
Volume of O2 at STP is given by
VO2(atSTP)=nO2×22.4
Where
nO2 is the number of moles of oxygen
Upon substituting the values, we get
VO2=7.40×22.4=5.25litre
So, option (C.) is also correct
Hence, the correct option is (D).
Note
Fractions as well as entire numbers can be stoichiometric coefficients. The coefficients help us, in essence, to determine the mole ratio between reactants and products.