To give 33.6 dm³ hydrogen gas at STP, 18.06 x 10²³ atoms of Na must react completely.
<h3>What is Mole concept ?</h3>
A mole is a unit of measurement used to measure the amount of any fundamental entity (atoms, molecules, ions) present in the substance.
As according to the given equation, 2 moles (ie 12.04 x 10²³ atoms) of Na-atoms produces 1 mole (22.4 ltr) of H₂-gas.
Hence, to produce 33.6 ltr (equivalent to 33.6 dm³) of H₂-gas produced by ;
= 12.04 x 10²³ atoms of Na / 22.4 ltr of H₂-gas x 33.6 ltr
= 18.06 x 10²³ atoms of Na
Hence, To give 33.6 dm³ hydrogen gas at STP, 18.06 x 10²³ atoms of Na must react completely.
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atomic mass=percentage of isotope a * mass of isotope a + percentage of isotope b * mass of isotope b+...+percentage of isotope n * mass of isotope n.
Data:
mass of isotope₁=267.8 u
percentage of isotope₁=90.3%
mass of isotope₂=270.9 u
percentage of isotope₂=9.7%
Therefore:
atomic mass=(0.903)(267.8 u)+(0.097)(270.9 u)=
=241.8234 u + 26.2773 u≈268.1 u
Answer: the mass atomic of this element would be 268.1 u
B) hydrogen gas burns in air.
explanation: the rest are physical properties.
Answer:

Explanation:
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In this case, since we know the balanced chemical reaction, we are first able to realize there is a 1:3 mole ratio between zinc phosphate and zinc chloride; it means that we can first compute the moles of the desired product via stoichiometry:

Next, since those moles are associated with the theoretical yield of zinc chloride, we obtain the corresponding mass:

Finally, we compute the percent yield by diving the actual yield (18 g) by the theoretical yield:

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