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3 years ago

#1: How many valence electrons are in the outermost shell of all halogens?

Chemistry

1 answer:

Kipish [7]3 years ago

3 0

#1: How many valence electrons are in the outermost shell of all halogens?
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what mass of sodium fluoride (FW=42.0 g/mol) must be added to 3.50 x 10^2 mL of water to give a solution with pH = 8.40?

MaRussiya [10]

Answer:

Explanation:

Sodium fluoride, being a salt, dissolves in water completely producing F ⁻ ions. Now F⁻ is the conjugate base of the weak acid HF, so in water we will have the following equilibrium:

F⁻ + H₂O ⇆ HF + OH⁻

Given this equilibrium, we need to calculate Kb from the Ka for HF, the [ OH ⁻] from the given pH, and finally the mass needed to produce that OH⁻ concentration.

The equilibrium constant, Kb , can be calculated from Kw = Ka x Kb, where Kw = 10⁻¹⁴ and Ka for HF is 6.6 x 10⁻⁴ from reference tables.

Kb = 10⁻¹⁴ / 6.6 x 10⁻⁴ = 1.5 x 10⁻¹¹

pH + pOH = 14 ⇒ pOH = 14 - 8.40 = 5.60

[ OH⁻ ] = 10^-5.60 = 2.51 x 10⁻⁶

Now we have all the information :

F⁻ HF OH⁻

Equilibrium X 2.51 x 10⁻⁶ 2.51 x 10⁻⁶

(2.51 x 10⁻⁶)² / X = 1.5 x 10⁻¹¹ ⇒ X = (2.51 x 10⁻⁶)² / 1.5 x 10⁻¹¹

X = [ F⁻ ] = 0.41 M

For 350 mL ( 0.35 L ) we need to add:

0.41 mol HF/ 1 L * 0.35 L = 0.144 mol

and finally the mass will be:

0.144 mol NaF * 42.0 g/mol NaF = 6.03 g NaF

7 0

2 years ago

A particular balloon can be stretched to a maximum surface area of 1257 cm2. The balloon is filled with 3.1 L of helium gas at a

lianna [129]

Answer:

P = 0.6815 atm

Explanation:

Pressure = 754 torr

The conversion of P(torr) to P(atm) is shown below:

$P(torr)=\frac {1}{760}\times P(atm)$

So,

Pressure = 754 / 760 atm = 0.9921 atm

Temperature = 294 K

Volume = 3.1 L

Using ideal gas equation as:

PV=nRT

where,

P is the pressure

V is the volume

n is the number of moles

T is the temperature

R is Gas constant having value = 0.0821 L.atm/K.mol

Applying the equation as:

0.9921 atm × 3.1 L = n × 0.0821 L.atm/K.mol × 294 K

⇒n of helium gas= 0.1274 moles

Surface are = 1257 cm²

For a sphere, Surface area = 4 × π × r² = 1257 cm²

r² = 1257 / 4 × π ≅ 100 cm²

r = 10 cm

The volume of the sphere is :

$V=\frac {4}{3}\times \pi\times r^3$

Where, V is the volume

r is the radius

$V=\frac {4}{3}\times \frac {22}{7}\times {10}^3$

V = 4190.4762 cm³

1 cm³ = 0.001 L

So, V (max) = 4.19 L

T = 273 K

n = 0.1274 moles

Using ideal gas equation as:

PV=nRT

Applying the equation as:

P × 4.19 L = 0.1274 × 0.0821 L.atm/K.mol × 273 K

P = 0.6815 atm

4 0

3 years ago

Which element is non-metallic and a gas at room temperature?

ANEK [815]

Answer:

Notrogen(N)

Explanation:

Plz mark me as brilliant

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2 years ago

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I have four neutrons and I'm metallic. Who am I?

Mekhanik [1.2K]

Beryllium has four neutrons

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3 years ago

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What NaCl NaCl concentration results when 249 mL 249 mL of a 0.850 M 0.850 M NaCl NaCl solution is mixed with 667 mL 667 mL of a

tamaranim1 [39]

Answer:

The answer to your question is 0.54M

Explanation:

Data

Final concentration = ?

Concentration 1 = 0.850 M

Volume 1 = 249 ml = 0.249 l

Concentration 2 = 0.420 M

Volume 2 = 0.667 M

Process

1.- Calculate the number of moles in both solutions

Number of moles 1 = Molarity 1 x Volume 1

= 0.850 x 0.249

= 0.212

Number of moles 2 = Molarity 2 x Volume 2

= 0.420 x 0.667

= 0.280

Total number of moles = 0.212 + 0.280

= 0.492

2.-Calculate the final volume

Final volume = Volume 1 + Volume 2

Final volume = 0.249 + 0.667

= 0.916 l

3.- Calculate Molarity

Molarity = 0.492 / 0.916

Molarity = 0.54

4 0

3 years ago