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2 years ago

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Chemistry

1 answer:

dimaraw [331]2 years ago

7 0

Answer:

neon gas

Explanation:

neon is a noble gas, meaning it has a full outer shell of elections. this means it is stable and is very unlikely to have a reaction with another substance.

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Explain how you would make 450 mL of a .250M NaOH solution?

Neporo4naja [7]

Answer:

Weigh 4.5 grams of sodium hydroxide and add it to the dry volumetric flask of 450 mL followed by small amount of water to dissolve all the NaOH .After this add the water upto tye mark of 450 mL.

Explanation:

Molarity of the solution is the moles of compound in 1 Liter solutions.

$Molarity=\frac{\text{Mass of compound}}{\text{Molar mas of compound}\times Volume (L)}$

Mass of NaOH = x

Molar mass of NaOH = 40 g/mol

Volume of the NaOH solution = 450 mL =- 0.450 L ( 1 ml = 0.450 L)

Molarity of the solution of NaOH = 0.250 M

$Molarity=\frac{1.248 g}{26 g/mol\times 0.9102254 L}=0.528 mol/L$

$0.250 M=\frac{x}{40 g/mol\times 0.450 L}$

Solving for x:

x = 4.5 g

Weigh 4.5 grams of sodium hydroxide and add it to the dry volumetric flask of 450 mL followed by small amount of water to dissolve all the NaOH .After this add the water upto tye mark of 450 mL.

4 0

3 years ago

What is the pH at the equivalence point in the titration of a 25.7 mL sample of a 0.370 M aqueous nitrous acid solution with a 0

expeople1 [14]

Answer:

pH = 8.24

Explanation:

Nitrous acid (HNO₂) reacts with KOH, thus:

HNO₂ + KOH → KNO₂ + H₂O

Moles of HNO₂ are:

0.0257mL ₓ (0.370mol / L) = 0.00951moles.

In equivalence point, the complete moles of nitrous acid reacts with KOH producing potassium nitrite. There are needed:

0.00951mol ₓ (1L / 0.491mol) = 0.01937L ≡ 19.4mL of 0.491M KOH to reach equivalence point.

Total volume in equivalence point is: 19.4mL + 25.7mL = 45.1mL

Potassium nitrite is in equilibrium with water, thus:

NO₂⁻ + H₂O ⇄ HNO₂ + OH⁻

Where equilibrium constant, Kb, is defined as:

Kb = 1.41x10⁻¹¹ = $\frac{[OH^-][HNO_2]}{[NO_2]}$

In equilibrium, molarity of each compound are:

[NO₂⁻]: 0.00951mol/0.00451L - X = 0.211M - X

[HNO₂]: X

[OH⁻]: X

Where X is reaction coordinate

Replacing in Kb:

1.41x10⁻¹¹ = $\frac{[X][X]}{[0.211 -X]}$

0 = X² + 1.41x10⁻¹¹X - 2.97x10⁻¹²

Solving for X:

X = -1.72x10⁻⁶ FALSE ANSWER. There is no negative concentrations.

X = 1.72x10⁻⁶. Right answer.

That means:

[OH⁻]: 1.72x10⁻⁶M

As pOH is -log [OH⁻] and pH = 14-pOH:

pOH = 5.76; pH = 8.24

3 0

3 years ago

Rank the members of each set of compounds in order of decreasing ionic character of their bonds. Use partial charges to indicate

Firdavs [7]

Answer:

Ionic character

A. PF₃ > PBr₃ > PCl₃

B. BF₃ > CF₄ > NF₃

C. TeF₄ > BrF₃ > SeF₄

Explanation:

The most electronegative element is fluorine, followed chlorine, phosphorous nitrogen etc.

Atoms with high electronegativity tend to form negative ions.

Ionic compounds formed between elements with high electronegativity difference.

% ionic character is directly proportional to electronegativity difference.
According to Pauling Scale E.n for F(4.0), O(3.5), N(3.0), C(2.5), B(2.0), P(2.19), Se(2.55) , Te (2.1), Cl(3.16) and Br(2.96)
ΔE.N (Electronegativity difference) between( P and F = 4 - 2.19 = 1.81), (P and Br = 2.96 - 2.19 = 0.77) , (P and Cl = 3.16 - 2.96 = 0.2 )

ΔE.N (Electronegativity difference) between( N and F = 4 - 3 = 1), (B and F = 4 - 2 = 2) , (C and F = 4 - 2.5 = 1.5 )

ΔE.N (Electronegativity difference) between( Se and F = 4 - 2.55 = 1.45), (F and Te = 4 - 2.1 = 1.9) , (F and Br = 4 - 2.19 = 1.81 )

6 0

2 years ago

what kind of evidence indicates a chemical change ?... a physical change? you may use examples to show softened.

SOVA2 [1]

Some things that can indicate a chemical change are change of odor, change of color, change in temperature or energy, such as the production or loss of heat. An example could be the rusting of metal, there would be a color change of going from a shiny silver to a dirty, splotchy red color. Some things that indicate a physical change are change of appearance like change of shape, etc. It can also be like a change between a solid to liquid to gas. For example, the cutting of a piece of paper.

3 0

3 years ago

Which statement applies to electronegativity?

densk [106]

Answer: The correct answer is Option A.

Explanation:

Electronegativity is defined as the tendency of an atom to attract the shared pair of electrons towards itself whenever a bond is formed.

This property increases as we move from left to right across a period because the number of charge on the nucleus gets increased and electrons are attracted more towards the nucleus.

This property decreases as we move from top to bottom in a group because the electrons get add up in the new shells which make them further away from the nucleus.

Thus, the correct answer is Option A.

7 0

2 years ago