<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.
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For all three questions, we will use the fact that
- molarity = (moles of solute)/(liters of solution)
1) For 175 mL of solution at 0.203 M, this means that:
- 0.203 = (moles of solute)/0.175
- moles of solute = 0.035523 mol
Considering the hydrochloric acid solution, if we have 0.035523 mol, then:
- 6.00 = 0.035523/(liters of solution)
- liters of solution = 0.035523/6.00 = 0.0059205 = <u>5.92 mL (to 3 sf)</u>
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2) If there is 20.3 mL = 0.0203 L, then:
- 8.20 = (moles of solute)/0.0203
- moles of solute = 0.16646 mol
This means that the molarity of the diluted solution is:
- 0.16646/(0.200) = <u>0.832 M (to 3 sf)</u>
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3) If we need 1.50 L of 0.700 M solution, then:
- 0.700 = (moles of solute)/1.50
- moles of solute = 1.05 mol
Considering the 9.36 M acid solution, from which we need 1.05 mol of perchloric acid from,
- 9.36 = 1.05/(liters of solution)
- liters of solution = 1.05/9.36, which is 0.11217948717949 L, or <u>112 mL (to 3 sf)</u>
The average atomic weight is, from the name itself, the average weight of all its naturally occurring isotopes. All you have to do is multiple the abundance of each isotope with its individual mass, then add them altogether.
Mass = (0.10*55)+(0.15*56)+(.75*57)
<em>Mass = 56.65 amu</em>
Answer:
1)The molar mass of an atom is simply the mass of one mole of identical atoms. However, most of the chemical elements are found on earth not as one isotope but as a mixture of isotopes, so the atoms of one element do not all have the same mass.
2)Equally important is the fact that one mole of a substance has a mass in grams numerically equal to the formula weight of that substance. Thus, one mole of an element has a mass in grams equal to the atomic weight of that element and contains 6.02 X 1023 atoms of the element.
