Question

Copper metal (Cu) reacts with silver nitrate (AgNO3) in aqueous solution to form Ag and Cu(NO3)2. An excess of AgNO3 is present. The balanced chemical equation is shown below. Cu + 2AgNO3 mc021-1.jpg Cu(NO3)2 + 2Ag The molar mass of Cu is 63.5 g/mol. The molar mass of Ag is 107.9 g/mol. What mass, in grams, of Ag is produced from reaction of 31.75 g of Cu? 26.95 107.9 215.91 431.82

Answer 1

Answer: 107.9 grams of Ag will be produced.

Explanation: Reaction of Copper metal with Silver nitrate follows:

$Cu(s)+2AgNO_3(aq.)\rightarrow 2Ag(s)+Cu(NO_3)_2(aq.)$

As $AgNO_3$ is present in excess, therefore Copper metal is considered as the limiting reagent because it limits the formation of product.

We are given 31.75 grams of Copper metal are used in the reaction

Molar mass of Copper = 63.5 g/mol.

Moles can be calculated by:

$Moles=\frac{\text{Given mass}}{\text{Molar mass}}$     ....(1)

$\text{Moles of Copper}=\frac{31.75g}{63.5g/mol}=0.5moles$

From the reaction, we see that

For every 1 mole of Copper metal, 2 moles of Ag are produced.

For 0.5 moles of Copper, moles of Ag produced = $\frac{2}{1}\times 0.5$

Moles of Ag produced = 1 mole

Mass of Ag produced can be calculated by using equation 1.

Mass of Ag produced will be = Moles × Molar mass

Molar mass of Ag = 107.9 g/mol

$\text{Mass of Ag produced}=1\times 107.9g/mol$

Mass of Ag produced = 107.9 g/mol

Answer 2

Toichiometry time! Remember to look at the equation for your molar ratios in other problems.
31.75 g Cu | 1 mol Cu | 2 mol Ag | 107.9 g Ag         6851.65⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻   →   ⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻⁻  = 107.9 g Ag       ∅        | 63.5 g Cu | 1 mol Cu | 1 mol Ag              63.5

There's also a shorter way to do this: Notice the molar ratio from Cu to Ag, which is 1:2. When you plug in 31.75 into your molar mass for Cu, it equals 1/2 mol. That also means that you have 1 mol Ag because of the ratio, qhich you can then plug into your molar mass, getting 107.9 as well.