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3 years ago

4. Which of the following statements explains the cause of lanthanide contraction?

Chemistry

1 answer:

yawa3891 [41]3 years ago

8 0

Answer:

B. PROTONS EXHIBIT STRONGER PULL ON OUTER f ORBITALS

Explanation:

Lanthanide contraction is the greater than normal decrease in the ionic radius of the lanthanide series from atomic number 57 to atomic number 71. This decrease is rather not expected of the ionic radii of these elements and they result in the greater decrease in the subsequent series of the lanthanides from the atomic number 72. The cause of which is as a result of the poor shielding effects of the nuclear charge around the electrons of the f orbitals. So therefore, protons are strongly pulled out of the 4f orbital and as a result of the poor shielding effect which causes the electrons of the 6s orbitals to be drawn more closer to the nucleus and hence resulting in a smaller atomic radii. It is worthy to note that the shielding effects of the inner electrons decreasing from s orbital to the f orbital; that is s > p > d > f. So from the decrease in the shielding effects from s to the f orbitals, lanthanide contraction results from the inability of the orbitals far away from s like the 4f orbiatls to shield the outermost shells of the lanthanide elements. So the cause of lanthanide contraction is the action of the protons which strongly pull the electrons of the f orbitals because of the poor shielding effects due to the distance of this orbital from the nucleus.

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Answer: The empirical formula for the given compound is $Cu_2S$

Explanation:

We are given:

Mass of pure compound containing copper and sulfur = 4.963 g

Mass of S = 1.000 g

Mass of Cu = (4.963 - 1.000) g = 3.963 g

To formulate the empirical formula, we need to follow some steps:

Step 1: Converting the given masses into moles.

Moles of Copper = $\frac{\text{Given mass of Copper}}{\text{Molar mass of Copper}}=\frac{3.963g}{63.55g/mole}=0.0624moles$

Moles of Sulfur = $\frac{\text{Given mass of Sulfur}}{\text{Molar mass of Sulfur}}=\frac{1.000g}{32g/mole}=0.0312moles$

Step 2: Calculating the mole ratio of the given elements.

For the mole ratio, we divide each value of the moles by the smallest number of moles calculated which is 0.0312 moles.

For Copper = $\frac{0.0624}{0.0312}=2$

For Sulfur = $\frac{0.0312}{0.0312}=1$

Step 3: Taking the mole ratio as their subscripts.

The ratio of Cu : S = 2 : 1

Hence, the empirical formula for the given compound is $Cu_2S$

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3 years ago

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4. Your mission, if you choose to accept it, is to make 10mmol/L acetate buffer, pH5.0. Beginning with 10mmol/L HAc, what concen

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Answer:

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Explanation:

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5,0 = 4,74 + log₁₀ $\frac{[CH_{3}COO^-]}{[CH_{3}COOH]}$

Solving:

1,82 = $\frac{[CH_{3}COO^-]}{[CH_{3}COOH]}$ (1)

As total concentration of acetate buffer is:

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Replacing (2) in (1)

[CH₃COOH] = 3,55 mM

And

[CH₃COO⁻] = 6,45 mM

Knowing that:

CH₃COOH + NaOH → CH₃COO⁻ + Na⁺ + H₂O

Having in the first 10mmol/L of CH₃COOH, you need to add 6,45 mmol/L of NaOH. to obtain in the last 6,45mmol/L of CH₃COO⁻ and 3,55mmol/L of CH₃COOH .

I hope it helps!

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Explanation:

In fact, rare earth elements are in the third column, on the left.

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This table is divided into rows and columns, which represent the periods and groups or families. For its location the atomic number and valence of each element was considered.

In this sense, the elements in the periodic table are mainly arranged as follows:

-Alkali metals and Alkaline Earth metals in the first two columns, on the left.

-Rare earth elements in the third column (rows 6 and 7), on the left.

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3 years ago

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