Question

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1⃣ What is the number of water molecules contained in a drop of water weighing 0.123 g and 78 g ​

Answer 1

Solution:-

Fir solving this question you must have read mole concept.

Here I have explained mole concept in summary.

1 mole of anything contain 6.022 x 10²³ molecules or atoms of substance depending on the fact that given substance is compound or element. 1 mole of any element have 6.022 x 10²³ atoms and 1 mole of any compound has 6.022 x 10²³ molecules of that compound.

using this information we can write

1 mole of water has 6.022 x 10²³ molecules of water or $H_2 O$

And also weight of 1 mole water is 18g

$\mathtt{\large1 \: mole = 18g}$

$\mathtt{.123g = .006 \: moles}$

$\mathtt{.006 moles = .006 \times 6.022 \times {10}^{23} molecules}$

$\mathtt{.006 \: moles = 3.6 \times {10}^{21} molecules}$

For 78g

$\mathtt{78g = 4 .3 \: moles}$

$\mathtt{4.3moles = 4.3 \times 6.022 \times {10}^{23} molecules}$

$\mathtt{4.3moles = 2.5\times {10}^{24} molecules}$

Answers:-

• .123g=3.6 x 10²¹ molecules
• 78g=2.5 x 10²⁴ molecules