Answer
There are necessary 0.607 g of $Na_2CrO_4$ to precipitate all the silver ions.
Work Step by Step
- Write the reaction between $Na_2CrO_4$ and $AgNO_3$:
$Na_2CrO_4(aq) + AgNO_3(aq) -- \gt Ag_2CrO_4(s) + NaNO_3(aq)$
- Balance the reaction. Begin with the number of sodium (Na) atoms:
$Na_2CrO_4(aq) + AgNO_3(aq) -- \gt Ag_2CrO_4(s) + 2NaNO_3(aq)$
- Balance the number of $Ag$ atoms:
$Na_2CrO_4(aq) + 2AgNO_3(aq) -- \gt Ag_2CrO_4(s) + 2NaNO_3(aq)$
- The equation is balanced.
1. The molar mass for $Na_2CrO_4$ is:
22.99* 2 + 52* 1 + 16.00* 4 = 161.98g/mol $(Na_2CrO_4)$
2. According to the balanced equation, each mole of $Na_2CrO_4$ reacts with 2 moles of $AgNO_3$.
3. The molarity of the $AgNO_3$ is equal to $0.100mol/L$
4. 1000 mL = 1 L
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Now, use these informations as conversion factors to find the $Na_2CrO_4$ required mass.
$75.0mL \times \frac{1L}{1000mL} \times \frac{0.100mol(AgNO_3)}{1L} \times \frac{1mol(Na_2CrO_4)}{2mol(AgNO_3)} \times \frac{161.98g(Na_2CrO_4)}{1mol(Na_2CrO_4)} = 0.607 g (Na_2CrO_4)$
