thermochemistry

Question

Calculate the grams of Ca(s) produced when 1.65 Amperes are passed through the cell shown below for 4.96 hours.

Ca+2(aq)+2Cl−1(aq)→Ca(s)+Cl2(g)

Answer 1

Hello Justin.

First, 1.65 Amperes can also be written as 1.65 coulombs per second.

Then change 4.96 hrs to seconds. 4.96 hours = 17856 seconds

Now we are ready to go to work:

Multiply 1.65 C/s X 17856 C. This will give you 29462 C.

Now we need to use the faraday so we can determine the moles of electrons involved. The faraday is 96485 C/mole of electrons.

Our next calculation is shown below:

(29462 C) X (1 mol electrons / 96485 C) = 0.305 moles of electrons

Next we need to convert moles of electrons to moles of metal. Look at the charge of the calcium ion in the given equation. The calcium ion is +2, and the product is neutral calcium. The difference in those charges is 2, which tells us that there are 2 moles of electrons for every one mole of calcium involved in the reaction.

(0.305 mol electrons) X (1 mol Ca / 2 mol electrons) = 0.153 mol Ca

The last step is the easiest, converting moles of calcium to grams of calcium. I will allow you the pleasure of converting moles to grams.