8.1 g of `K_2Cr_2O_7` reacts with 12.8 g of HI according to the equation
`Cr_2O_7^(2-)+HItoCrI_3+KI+I_2`
Calculate:
(a). Percentage by mass of `K_2Cr_2O_7` left unreacted.
(b). Volume of `I_2` (g) evolved, if `I_2` obtained is heated to 500 K and 1.0 atm pressure.

Explanation

To solve the problem step by step, we will break it down into two parts as requested: (a) calculating the percentage by mass of `K_2Cr_2O_7` left unreacted, and (b) calculating the volume of `I_2` evolved.

### Step-by-Step Solution

### (a) Percentage by mass of `K_2Cr_2O_7` left unreacted

1. **Write the balanced chemical equation:**
The balanced equation for the reaction is:
...