Question

How many grams of oxygen are in 2 moles of potassium dichromate, $ {{{K}}_{{2}}}{{C}}{{{r}}_{{2}}}{{{O}}_{{7}}} $ ?

Answer 1

Hint: In the above question, we are provided a chemical formula of potassium dichromate and asked to find the weight of oxygen present. In one mole of potassium dichromate, the number of oxygen atoms can be determined from the formula and then we can find the number of oxygen atoms present in 2 moles. After that we simply have to find its weight.

Complete step by step solution
In the above question, we are given the formula of potassium dichromate as $ {{{K}}_{{2}}}{{C}}{{{r}}_{{2}}}{{{O}}_{{7}}} $ .
We can easily infer that, in 1 mole of $ {{{K}}_{{2}}}{{C}}{{{r}}_{{2}}}{{{O}}_{{7}}} $ , 7 atoms of oxygen are present.
So, in 2 moles of $ {{{K}}_{{2}}}{{C}}{{{r}}_{{2}}}{{{O}}_{{7}}} $ , 14 atoms of oxygen will be present.
The atomic mass of oxygen is 16.
So, the weight of 14 oxygen atoms = $ {{14 \times }} $ atomic mass of oxygen = $ {{14 \times 16 = 224}} $ g
Hence, 224 g of oxygen are present in 2 moles of potassium dichromate, $ {{{K}}_{{2}}}{{C}}{{{r}}_{{2}}}{{{O}}_{{7}}} $ .

Additional Information
The colour of potassium dichromate varies from orange to red. It is a crystalline, inorganic compound that emits toxic chromium fumes upon heating. It is highly corrosive and is a strong oxidizing agent.

Note
In these types of questions, where we are asked to find out the number of elements present in a compound, then, we have to just look at the number which is present in the base of the element to know about the number of atoms present and hence, we can find its weight by number of moles formula.