Question

how many hydrogen atoms are in 78.4 grams of hydrochloric acid

Answer 1

You should get about 78.4 g H. Convert grams of HCl to moles of HCl by finding total atomic mass of HCl. From there, convert mole of HCl to moles of H which is 1. Last, convert moles of H to g H which is 1g and you should get your answer. Don't forget significant figures. Since you are given 3 in your given information, your answer should have 3 significant figures.

Answer 2

Answer: $12.95\times 10^{23}$

Explanation:

$Moles=\frac{\text{Given mass}}{\text{Molar mass}}$

${\text {Moles of HCl}=\frac{78.4g}{36.5g/mol}=2.15$

According to Avogadro's law, 1 mole of every substance contains Avogadro's number of particles.

1 mole of HCl contains=$6.023\times 10^{23}$ atoms of Hydrogen

2.15 moles of HCl contains=$\frac{6.023\times 10^{23}}{1}\times 2.15=12.95\times 10^{23}$ atoms of hydrogen.