CHEMISTRY HIGH SCHOOL

At any given location, the physical properties of a substance do not change. a. True
b. False

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Answer 1
Answer: It is true that at any given location, the physical properties of a substance do not change. 

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Is the following chemical equation balanced?

2Na + 2H2O 2NaOH + H2

Answers

Answer:  YES

Explanation:  The given chemical equation can be balanced by balancing the stiochiometric number of each and every element.

This rule is in accordance with the Law of Conservation of Masses which states that the masses of the elements in any chemical equation are constant at any instant of time.

Thus the given equation can be written as

                  2Na + 2H2O \rightleftharpoons  2NaOH + H2
sure !

equation balanced:

2 Na + 2 H₂O = 2 NaOH + H₂  ( single replacement )

hope this helps!

________ occurs when gravity is the only force acting on an object. Select the best answer from the choices below.

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Free Fall is when the only force acting on an object is gravity.

2H2 + O2 mc002-1.jpg 2H2O The number of moles of hydrogen that is needed to produce 0.253 mol of water is

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Answer : The number of moles of hydrogen gas needed are, 0.253 mole

Explanation : Given,

Moles of water = 0.253 mole

Now we have to calculate the moles of hydrogen gas.

The given balanced chemical reaction is,

2H_2+O_2\rightarrow 2H_2O

From the balanced reaction we conclude that,

As, 2 moles of water obtained from 2 moles of hydrogen gas

So, 0.253 moles of water obtained from (2)/(2)* 0.253=0.253mole of hydrogen gas

Therefore, the number of moles of hydrogen gas needed are, 0.253 mole
Mol --> Mol is a one step, XMol H2 = .253mol H20 x 2/2 = .253 mol H2

For the amino acid alanine, the major species in solution at pH 7 is the zwitterionic form, which has a negatively charged carboxylic acid group and a positively charged amino group. There is a less common neutral form in which neither group is charged. The carboxylic acid group of alanine has a p K a of 3 . The amino group of alanine has a p K a of 8 . Estimate the ratio of the concentration of the neutral amino acid species to the zwitterionic species at pH 7 .

Answers

Answer: ratio is 10⁻⁵

Explanation:

From Acid-dissociation equilibrium constant, HA is given thus,

HA + H₂O  ⇄ H₃O⁺ + A⁻

equilibrium constant, Ka = [H₃O⁺] [A⁻] / [HA]

[H₃O⁺]  = Ka [HA] / [A⁻]

from this we have that

pH = -log[H₃O⁺]

and pKa = -logKa

Applying Henderson-Hassel bach equation;

pH = pKa + log  [A⁻]/[HA] ...........(1)

A⁻ rep the salt and HA rep the acid

at a given pH of 7, the pKa value of carboxylic acid COOH is 3

∴ from equation (1).

7 = 3 + log(COO⁻/COOH)

log(COO⁻/COOH) = 4

thus (COO⁻/COOH) = 10⁻⁴ ...................(2)

The ratio of alanine COOH to COO- at pH 7 is  (COO⁻/COOH) = 10⁻⁴

(ii) Also considering the ratio of alanine NH2 to NH3+ at pH 7  we have;

given Pka value is 8,

therefore pH = pKa + log [salt]/[base]

7 = 8 + log (NH₂/NH₃)

(NH₂/NH₃) = 10⁻¹

thus the ratio of the concentration of the neutral amino acid species to the zwitterionic species at pH 7 is;

10⁻⁴ ˣ 10⁻¹ = 10⁻⁵

cheers i hope this helps

What is the frequency of radiation that has a wavelength of 1.73 nm? (HINT: Don't forget that you have to convert nm to m first.)

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