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lions [1.4K]
2 years ago
14

Round off each of the following numbers to two significant figures:

Chemistry
2 answers:
Kay [80]2 years ago
7 0
A) 5.2 x 10^2
B) 86.
C) 6.4 x 10^3
D) 5.0
E) 22.
F) 0.89
strojnjashka [21]2 years ago
7 0

Answer:

(a) 5.1 × 10²

(b) 86

(c) 6.4 × 10³

(d) 5.0

(e) 22

(f) 0.89

Explanation:

To round off a number, we consider the number that is to its right. If that number is 5 or higher, we increase the number of interest. If the number to the right is 4 or lower, the number of interest remains the same. When taking less significant figures, we might need to use scientific notation for large or small numbers.

<em>Round off each of the following numbers to </em><em>two</em><em> significant figures: </em>

<em>(a) 517</em>   → 5.1 × 10²

<em>(b) 86.3</em>  → 86

<em>(c) 6.382 × 10³ </em> → 6.4 × 10³

<em>(d) 5.0008</em>  → 5.0

<em>(e) 22.497</em>  → 22

<em>(f) 0.885</em> → 0.89

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Answer:

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Explanation:

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2 years ago
A certain radioactive atom has 90 protons and 142 neutrons. If this atom undergoes alpha decay, what is the mass number of the d
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Answer: the mass number of the daugther atom is 232,


Explanation:


1) Alpha (α) decay is a nuclear reaction in which a nucleus (parent's nucleus) emits an alpha (α) particle and leads to a different atom (daughter atom).


2) The alpha (α) particle is a nucleus of helium atom, i,e, a nucleus with two protons and two neutrons. The symbol used for the α particles is <em>⁴₂He</em>, where the superscript 4 indicates the mass number (2 protons + 2 neutrons = mass number 4), and the subscript 2 indicates the atomic number (number of protons).


3) Then, to determine the mass number of the daughter atom you just need to do a mass number balance:


mass number of the parent atom = mass number of the daugther atom + mass number of the α particle.


The mass number of the radioactive (parent) atom is 90 protons + 142 neutrons = 232.


∴ 232 = x + 4 ⇒ x = 232 - 4 = 228 ← answer.


The full equation may help you to have a wider vision of the problem:


²³²₉₀ X → ⁴₂ He + ²²⁸₈₈ Y

Note this:

  • 232 = 4 + 228 (this is a mass number balance)
  • 90 = 2 + 88 (this is an atomic number balance)
  • X is the parent atom, and Y is the daughter atom
  • You can use a periodic table to determine the identity of the unknown atoms (using the atomic numbers).
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How do both plants and animals fight pathogens. A.both have a protective outer layer B.both have an antigen-antibody response C.
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What is the total E associated with one mole of photons (a unit known as the Einstein) of 3.91x1019 Hz?
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Answer:

        E=1.56\times 10^{10}J

Explanation:

The<em> energy of a photon</em>, E, can be calculated with the Planck-Einstein equation:

          E=hf

Where:

  • h is Planck's constant 6.626×10⁻³⁴ J.s, and
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Substituting with your data:

          E=6.626\times 10^{-34}J.s\times 3.91\times 10^{19}s^{-1}=2.5908\times 10^{-14}J

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          E=2.5908\times 10^{-14}J\times 6.022\times 10^{23}=1.56\times 10^{10}J

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