I saw another topic similar to this, but as mentioned, my standard deviation should therefore be 1, and it's not... Have I done something wrong?

Twelve samples of blister copper are extracted from an anode refining furnace to estimate the arsenic content. The following concentrations (ppm) are obtained: 6.1, 4.0, 3.4, 6.2, 3.0, 5.1, 4.8, 5.2, 4.6, 5.2, 3.9, 4.3. Can you assume that the distribution of arsenic content follows a normal distribution? Justify your argument.

I got the mean to be 4.65 and the standard deviation to be 16.1. That HAS to be wrong... but ARGH! No matter what I do I get that!

Please help, Thanks!