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Ostrovityanka [42]
3 years ago
7

What is the second most abundant element in stars? A. helium B. iron C. hydrogen D. oxygen

Chemistry
1 answer:
devlian [24]3 years ago
8 0
<span>The </span>abundance of a chemical element<span> is a measure of the </span>occurrence<span> of the </span>element<span> relative to all other elements in a given environment. Abundance is measured in one of three ways: by the </span>mass-fraction<span> (the same as weight fraction); by the </span>mole-fraction<span> (fraction of atoms by numerical count, or sometimes fraction of molecules in gases); or by the </span>volume-fraction<span>. Volume-fraction is a common abundance measure in mixed gases such as planetary atmospheres, and is similar in value to molecular mole-fraction for gas mixtures at relatively low densities and pressures, and </span>ideal gas<span> mixtures. Most abundance values in this article are given as mass-fractions.

</span>
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A solution has a pOH of 8.7 so what is the pH of the solution? Is the solution acidic, basic, or neutral?
RSB [31]
PH + pOH = 14

pH = 14 - pOH

pH = 14 - 8.7

pH = 5,3

This solution is <u>acidic</u>.

If pH<7 - acidic
If pH=7 - neutral
If pH>7 - basic
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3 years ago
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What effect does mass have on an objects density?
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The density of an object or quantity of matter is its mass divided by its volume.
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If 20.0 grams of Al is placed into a solution containg
meriva

Answer:

m H2(g) = 2.241 g H2(g)

Explanation:

  • 2Al(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 3 H2(g)

limit reagent:

∴ Mw Al = 26.982 g/mol

∴ Mw H2SO4 = 98.0785 g/mol

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⇒ n H2SO4 = ( 115 g H2SO4 )×(mol/98.0785 g) = 1.173 mol H2SO4

⇒ n H2 = (0.7412 mol Al)×(3 mol H2/ 2 mol Al) = 1.112 mol H2

∴ Mw H2 = 2.016 g/mol

⇒ g H2 = (1.112 mol H2)×(2.016 g/mol) = 2.241 g H2

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3 years ago
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lianna [129]

Reduction half reaction: Cu²⁺(aq) + 2e⁻ → Cu⁰(s).


Oxidation half reaction: NO₂⁻(aq) + H₂O(l) → NO₃⁻(aq) + 2H⁺(aq) + 2e⁻.  

Balanced chemical reaction:

Cu²⁺(aq) + NO₂⁻(aq) + H₂O(l) → Cu(s) + NO₃⁻(aq) + 2H⁺(aq).

Copper is reduced from oxidation number +2 (Cu²⁺) to oxidation number 0 (Cu) and nitrogen is oxidized from oxidation number +3 (in NO₂⁻) to oxidation number +5 (in NO₃⁻).


8 0
2 years ago
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