Answer:
1. D
2. B
Explanation:
1. Isotopes vary in neutrons. Due to this variance, the difference in neutrons change the mass of the element.
Note: the amount of protons in an element never changes. The number of protons (the atomic number on the periodic table) identifies the element in question. If you add or subtract protons, you change the element.
2. B-10 and B-11 are two isotopes of the element Boron: One with 10 neutrons, and another with 11 neutrons. Because they contain a variance of neutrons, they do not have the same mass. This cancels choices A and D.
The protons of an element are equal to the atomic number of that element. Borons atomic number is 5 (according to the periodic table), so it contains 5 protons. This cancels choice C as the element with 6 protons is Carbon.
Note: The amount of protons in an atom is balanced out by the same amount of electrons to allow for a neutral charge of the element (i.e., the protons, which contain a positive charge, and electrons, which contain a negative charge, cancel each other out. In the case of Boron: +5 protons - 5 electrons = 0 charge). This is why choice B is correct, as the consideration of an ion is not necessary for this question.
Answer:
3 moles of CO are needed
Explanation:
Given data:
Number of moles of CO used = ?
Mass of Fe produced = 112 g
Solution:
Chemical equation:
Fe₂O₃ + 3CO → 2Fe + 3CO₂
Number of moles of Fe:
Number of moles = mass/ molar mass
Number of moles = 112 g/ 55.85 g/mol
Number of moles = 2.00 mol
Now we will compare the moles of iron and CO.
Fe : CO
2 : 3
Thus, 3 moles of CO are needed.
Answer:
option c
Explanation:
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Answer:
2.08 moles (3 s.f.)
Explanation:
number of moles
= number of atoms ÷ Avogadro's constant
Avogadro's constant= 6.022 ×10²³
Thus, number of moles
= 1.25×10²⁴ ÷ (6.022 ×10²³)
= 2.08 moles (3 s.f.)
