Question

1 tonne of CuSO4 contains how many kg of copper? (Mr; Cu=63.5, S=32, O=16)

Options
a) 63.5/159.5 * 1000 b) 63.5/96 * 1000 c) 63.5/159.5 * 1 d) 63.5/159.5 * 1/1000

Answer 1

a) `63.5/159.5 × 1000`

Explanation:

Let's look at the formula of copper(II) sulfate.#.

`A_text(r) = 63.5 color(white)(mll)32 color(white)(mm)16`
`color(blue)(color(white)(mmml)"Cu"color(white)(mm)"S"color(white)(mml)"O"_4)`
`M_text(r) = "63.5 + 32 + 4×16 = 159.5"`

The formula tells you that there are 63.5 units of copper in 159.5 units of `"CuSO"_4`

The units can be anything you want.

We usually use grams, but they could be micrograms, kilograms, tonnes, pounds, etc.

Thus, in 1 t of `"CuSO"_4` you have

`"Mass of Cu" = 1000 color(red)(cancel(color(black)("kg CuSO"_4))) ×"63.5 kg Cu"/(159.5color(red)(cancel(color(black)("kg CuSO"_4)))) = "398 kg Cu"`

Thus the numbers in the calculation are `1000 ×63.5/159.5`.

This question is an excellent example of why you should always use units in your calculations.

If the units don't cancel correctly, you know you have done something wrong.