20 分** 1 條Form 2 數,, 入黎睇下啦...

有1 mole的水 (先別理會1 mole有多少, 知道是用來計算水分子數目的單位就行了),
其重量為18.0153克,
而每個水分子的重量為2.9915 × 10-23克,
要知道水分子的數目,
用水的整體重量除以每個水分子的重量就可以了,
即 18.0153 / 2.9915 × 10-23 = 6.02 × 1023 (to 3 sig. fig.)

其實條數有少少about chem
let y be the no. of water molecules of one mole of water
one mole of water = 18.0153g
one water molecule = 2.9915 X 10^-23g
y water molecules= (2.9915 X 10^-23)g X y
one mole of water contains y water molecules
one mole of water = y water molecules
18.0153g = (2.9915 X 10^-23)g X y
y = 18.0153g/ (2.9915 X 10^-23)g
=6.02 X 10^23