Sig Fig Significant Digits question quick!?

The question was how many moles of solute are needed per 1 kg of water when a compound is used in some antifreeze mixtures. they want protection against freezing to as low as -40 C. -40 is the only number in the problem. The answer I got is 21.5 but what is the answer using correct significant digits?

Sig Fig Significant Digits question quick!?
Assume the temperature (-40) is exact, so infinite sig figs.



ΔTf = Kf · mB

40 = 1.86 * m

21.50537634 = m

21.5 = m



3 sig figs is correct.
Reply:2.2X10^1 You must use scientific notation because the problem contains two significant figures.

The answer needs a decimal place in it... just like 1.0 there really is no need for the decimal place in most situations, but in chemistry class it is best.
Reply:This question shows just how daft "significant figures" problems are (not your fault; you didn't choose the question). In this case, whatever the rules state, is just as easy to measure out 21.5 mol as 21 or 22 mol, and there is no point being less accurate than you could be.



So if you have a good teacher, tell him or her that you know that 21 is the official answer, but pass on my comments, and see what the teacher says.
Reply:Delta T = kf x m

kf for water = 1.86

40 = 1.86 x m

m = 21.5

this means 21.5 moles of solute in 1 Kg of water

Since 2 significant figures are in 40 °C the answer would be 22 moles
Reply:20 C