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4 years ago

13

boron has two naturally occurring isotopes: boron -10 (abundance = 19.8% , mass = 10.013 amu) boron -11 (abundance = 80.2%, mass

= 11.009 amu) Calculate th eatomic mass of boron

1 answer:

Mariulka [41]4 years ago

6 0

Explanation:

eam=%abudance×mass+%abudance×mass

eam=19.8%×10.013/100+80.2%×11.009/100

eam=198.2574/100+882.9218/100

eam=1081.1792/100

eam=10.811792

eam=10.812

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3 years ago

Graphite and iodine are non metal but they shine why secondry school

Alex_Xolod [135]

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3 years ago

Which of the following is true about the melting temperature of potassium chloride? The melting temperature is relatively high.

allochka39001 [22]

Answer:f

First option: <em>the melting temperature is relatively high.</em>

Explanation:

You can look at the melting temperature at any table that summarizes the main properties of this compound, <em>potassium chloride</em>.

Such melting point is 770 °C, which is relatively high.

<u>Why is this?</u>

Potassium chloride is a ionic compound formed by the cations of potassium, K⁺, and the chloride anions, Cl⁻. Its unit formula is KCl.

The ionic bond between K and Cl is possible because each K atom is able to yield its valence electron to one Cl atom which has 7 valence electrons.

Then, the K atoms become positive ions (cations) K⁺, while Cl atoms become negative ions (Cl⁻).

These two ions with opposite charge are bonded by the force of electrostatic attraction. This is a ionic bond.

<em>Melting point</em>, so as boiling point along with other physical properties, depends on the attraction force between the atoms.

Hence, since the attrative forces between the ions are relatively strong, the <em>melting point</em> of the ionic compounds, such as potassium chloride, are <em>relatively high.</em>

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3 years ago

Aspirin is a weak organic acid whose molecular formula is HC9H7O4. An aqueous solution of aspirin is prepared by dissolving 3.60

garri49 [273]

Answer:

Ka = 3.50x10⁻⁴

Explanation:

First, we need to convert the unit of 3.60 g/L to mol/L:

$C_{C_{9}H_{8}O_{4}} = 3.60 \frac{g}{L}*\frac{1 mol}{180.16 g} = 0.0200 mol/L$

The reaction dissociation of aspirin in water is:

C₉H₈O₄ + H₂O ⇄ C₉H₇O₄⁻ + H₃O⁺

0.02 - x x x

The constant of the above reaction is:

$Ka = \frac{[C_{9}H_{7}O_{4}^{-}][H_{3}O^{+}]}{[C_{9}H_{8}O_{4}]}$

$Ka = \frac{x^{2}}{0.02 - x}$

To find Ka we need to find the value of x. We know that pH = 2.6 so:

$pH = -log[H_{3}O^{+}]$

$2.6 = -log(x)$

$x = 2.51 \cdot 10^{-3} M = [H_{3}O^{+}] = [C_{9}H_{7}O_{4}^{-}]$

Now, the concentration of C₉H₈O₄ is:

$C_{C_{9}H_{8}O_{4}} = 0.02 - 2.51 \cdot 10^{-3} = 0.018 M$

Finally, Ka is:

$Ka = \frac{[C_{9}H_{7}O_{4}^{-}][H_{3}O^{+}]}{[C_{9}H_{8}O_{4}]} = \frac{(2.51 \cdot 10^{-3})^{2}}{0.018} = 3.50 \cdot 10^{-4}$

Therefore, the Ka of aspirin is 3.50x10⁻⁴.

I hope it helps you!

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3 years ago

What is the mass, in grams, of 2.50 * 10-3 mol of aluminum sulfate?

Nonamiya [84]

Answer:

The mass is 0.855 grams (option A)

Explanation:

Step 1: Data given

aluminium sulfate = Al2(SO4)3

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Step 2: Calculate molar mass Al2(SO4)3

Molar mass = 2* 26.99 + 3*32.065 + 12*16

Molar mas = 342.175 g/mol

Step 3: Calculate mass Al2(SO4)3

Mass Al2(SO4)3 = moles Al2(SO4)3 * molar mass Al2(SO4)3

Mass Al2(SO4)3 = 2.5 *10^-3 moles * 342.175 g/mol

Mass Al2(SO4)3 = 0.855 grams

The mass is 0.855 grams (option A)

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3 years ago