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Ilia_Sergeevich [38]
3 years ago
6

The mass spectrum of a hypothetical element shows that 78.21% of the atoms have a mass of 27.977 u, 1.346% have a mass of 28.976

u, and the remaining have a mass of 29.974 u. Calculate the average atomic mass of this element (in units of u). (Use 4 Sig. Fig. Don't round until end.)
Chemistry
1 answer:
Crank3 years ago
4 0

Answer: 28.40

Explanation:

For A(27.977 u)

Mass number = 27.977

Abundance = 78.21%

For B (28.976 u)

Mass number = 28.976

Abundance = 1.346%

For C(29.974 u)

Mass number = 29.974

Abundance = 20.444%

Averages atomic mass

= (Mass of A x abundance of A)/100 + (Mass of B x abundance of B)/100 + (Mass of C x abundance of C)/100

= (27.977x78.21)/100 + (28.976x1.346)/100 + (29.974x20.444)/100

= 21.8808117 + 0.39001696 + 6.12788456

= 28.40

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Answer:

pH = 12.15

Explanation:

To determine the pH of the HCl and KOH mixture, we need to know that the reaction is  a neutralization type.

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We need to determine the moles of each compound

M = mmol / V (mL) → 30 mL . 0.10 M = 3 mmoles of HCl

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The base is in excess, so the HCl will completely react and we would produce the same mmoles of KCl

HCl  +  KOH  →  H₂O  +  KCl

3 m       4 m                       -

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As the KCl is a neutral salt, it does not have any effect on the pH, so the pH will be affected, by the strong base.

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3 years ago
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Explanation:

Given data:

Mass of beryllium needed = ?

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Solution:

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now we will calculate the number of moles of nitrogen:

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Number of moles = 0.675 mol

Now we will compare the moles of nitrogen and Be from balance chemical equation.

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Number of moles of Be needed are 2.03 mol.

Mass of Beryllium:

Mass = number of moles × molar mass

Mass = 2.03 mol ×   9.01 g/mol

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