Question

quantas moléculas de água possuem em uma amostra de 4,5g?​

Answer 1

$\boxed{\begin{array}{l}\sf m_{H_2O} =2\cdot1+16=18g/mol\\\sf 18~g\longrightarrow6\cdot10^{23}\\\sf4,5\longrightarrow x\\\sf 18x=27\cdot10^{23}\\\sf x=\dfrac{27\cdot10^{23}}{18}\\\sf x=1,5\cdot10^{23}~mol\acute eculas\end{array}}$