# 100mL of 5mol L-1 nitric acid was added to excess copper. What mass of copper reacted? Cu +4HNO3 -> 2NO2 + Cu(NO3)2

Aug 5, 2017

The mass of $\text{Cu}$ was d) 7.9 g.

#### Explanation:

Step 1. Start with the balanced equation.

"Cu" + "4HNO"_3 → "2NO"_2 + "Cu"("NO"_3)_2

Step 2. Calculate the moles of ${\text{HNO}}_{3}$.

${\text{Moles of HNO"_3 = 0.100 color(red)(cancel(color(black)("L HNO"_3))) × ("5 mol HNO"_3)/(1 color(red)(cancel(color(black)("L HNO"_3)))) = "0.50 mol HNO}}_{3}$

Step 3. Calculate the moles of $\text{Cu}$

$\text{Moles of Cu" = 0.50 color(red)(cancel(color(black)("mol HNO"_3))) × "1 mol Cu"/(4color(red)(cancel(color(black)("mol HNO"_3)))) = "0.12 mol Cu}$

4. Calculate the mass of $\text{Cu}$.

$\text{Mass of Cu" = 0.12 color(red)(cancel(color(black)("mol Cu"))) × "63.55 g Cu"/(1 color(red)(cancel(color(black)("mol Cu")))) = "7.9 g Cu}$

Note: The answer can have only 1 significant figure, because that is all you gave for the concentration of the nitric acid.

However, I calculated the answer to two significant figures for you.