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4 years ago

A student explained to the class that helium has 8 valence electrons because it is in group 18. Is the student correct?

1 answer:

5 0

The student is incorrect because helium has 2 valence electrons and it's in group 18 because the first energy level is full. Although helium is placed in Group 18 which generally has 8 valence electrons, it does not have 8 valence electrons as the student suggested. It was grouped together with the noble gases because it exhibits similar properties with them.

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PLEASE HELP!!!!!!

jeyben [28]

Answer: The correct option is 1 mole of acetic acid was required for 2 moles of sodium bicarbonate

Explanation:

We are given:

Average number of drops of sodium bicarbonate = 142

The chemical equation for the reaction of sodium bicarbonate and acetic acid in vinegar follows:

$NaHCO_3+CH_3COOH\rightarrow CH_3COONa+H_2CO_3$

From the stoichiometry of the reaction:

1 mole of sodium carbonate reacts with 1 mole of acetic acid in vinegar.

Hence, the correct option is 1 mole of acetic acid was required for 2 moles of sodium bicarbonate

4 0

3 years ago

Given the molar absorptivity for a species X of 1600 M-1cm-1 at a wavelength of 270 nm, and 400 M-1cm-1 at a wavelength of 540 n

Andre45 [30]

Answer:

Explanation:

From the given information:

At wavelength = 270 nm

$\varepsilon x_1 = 1600 \ m^{-1} \ cm^{-1} \\ \\ \varepsilon y_1 = 200 \ m^{-1} \ cm^{-1}$

At 270 nm

Suppose x is said to be the solution for the concentration of x and y to be the solution for the concentration of y;

Then:

$\varepsilon x_1 \ l + \varepsilon y_1 \ l= 0.5 \\ \\ A = A_1 + A_2$

$1600 xl + 200 yl= 0.5$

Divide both sides by 200

$8xl + yl = \dfrac{0.5}{200}$

$8x + y = \dfrac{0.5}{200}l$

Use l = 1cm (i.e the standard length)

Then;

$8x + y = \dfrac{0.5}{200} ---- (1)$

For 540 nm:

$\varepsilon x_2 x \ l + \varepsilon y_2 y \ l= 0.5 \\ \\ 40 xl + 800 yl = 0.5$

$x + 20 y = \dfrac{0.5}{400 \ l}$

since l = 1

$x + 20 y = \dfrac{0.5}{400 \ } --- (2)$

Equating both (1) and (2) together, we have:

$8x + y - 8x - 160 y = \dfrac{0.5}{200} - \dfrac{0.5 \times 8}{400} \\ \\ \implies - 159 y = \dfrac{0.5}{200} ( 1 - \dfrac{8}{2}) \\ \\ -159 y = \dfrac{-0.5 \times 3}{200} \\ \\ 159 \ y = 0.0075 \\ \\ y = \dfrac{0.0075}{159} \\ \\ y = 0.00004716 \\ \\ y = 4.7 \times 10^{-5 } \ M$

3 0

3 years ago

1 Select the correct answer! Which statement best explains the octet rule? A. Atoms gain, lose, or share electrons to achieve a

Ostrovityanka [42]

Answer:

A. Atoms gain, lose, or share electrons to achieve a full valence shell

Explanation:

The octet rule is best explained as the process in which atoms lose or gain or share electrons to achieve a full valence shell.

In this process bonds are formed when there is an attraction between the two substances.
For electrovalent compounds, an atom will lose electrons or gain electron to form an ion, the electrostatic attraction causes the bond formation.
Covalent compounds, form by sharing of electrons.

Therefore, the octet rule is attained when atoms gain full valence configuration.

5 0

3 years ago

Determine how many significant figures are in each measurement.(9pts)

Strike441 [17]

1. 3 significant figures
2. 5 significant figures
3. 3 significant figures
4. 4 significant figures
5. 5 significant figures
6. 2 significant figures
7. 4 significant figures
8. 1 significant figure
9. 4 significant figures

5 0

3 years ago

Why is it advisable to keep the storage bottle containing the naoh solution closed?

Gennadij [26K]

The pure form of sodium hydroxide is solid. Compared to the pure form, the aqueous form of the liquid is actually many times more volatile. For this very reason, it is advised that the bottles used to keep samples of NaOH be kept closed.

5 0

3 years ago