Question

thr number of water molecules present in a drop of water weighing 0.018gm is

Answer 1

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$\sf{\underline{Given \ mass \ of \ water}}$ $\sf{= 0.018 \ g}$

$\sf{\underline{Molar \ mass \ of \ water \ ( H_2O)}}$$\rightarrow$

$\sf{= 2m_H + m_O}$

$\sf{= 2 ( 1 ) + 16}$

$\sf{= 18 \ g}$

${\boxed{\sf{No. \ of \ moles = {\dfrac{Given \ mass}{Molar \ mass}}}}}$

$\sf{No. \ of \ moles = {\dfrac{0.018 \ g}{18 \ g}}}$

$\sf{No. \ of \ moles = 0.001}$

${\boxed{\sf{No. \ of \ molecules = No. \ of \ moles × Avogadro's \ constant}}}$

$\sf{No. \ of \ molecules = 0.001 × 6.022 × {10}^{23}}$

$\large\sf\red{No. \ of \ molecules = 6.022 × {10}^{20}}$