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3 years ago

When might a theory or scientific claim be modified or changed?

1 answer:

4 0

Whenever new evidence is discovered we must make changes in order to adapt theories to the current base of knowledge. If we were to simply never change any scientific theory, then they would likely no longer stand as factual credible pieces of information in the future.

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According to VSEPR theory what causes molecular shapes to form?

iogann1982 [59]

Answer:

C: the repulsion of electrons and electrons.

Explanation:

According to the VSEPR theory, molecular shapes adjust so that the electrons can be as far apart as possible due to electrons repelling each other, which would mean the only possible answer is C.

5 0

3 years ago

At STP, what is the volume of 5.13 mol of nitrogen gas? Answer in units of L.

Gre4nikov [31]

Answer: $114.91L$

Explanation:

You need to know the conversion factor first in order to solve this. Any gas occupies 22.4L per mol.

$5.13mol(\frac{22.4L}{1mol})= 114.91L$ of nitrogen gas.

7 0

3 years ago

Use the atom builder interactive to identify each nucleus. Two protons represented as purple spheres and one neutron represented

aleksandr82 [10.1K]

Answer:

$\frac{3}{2}He$

$\frac{6}{2} He$

$\frac{7}{4}Be$

$\frac{3}{1} H$

$\frac{6}{4}Be$

$\frac{7}{3} Li$

Explanation:

In the first nucleus we are told that there are two protons and one neutron. Let us remember that the mass number = number of protons + number of neutrons.

This implies that, for the first specie the mass number is 3, for the second specie the mass number is 6 and the third specie has a mass number of 7 and so on. The mass number is indicated as a superscript.

The atomic number is the number of protons in the nucleus of the atom and helps us to identify the atom. It is always written as a subscript as shown.

5 0

3 years ago

During chemistry, Dan mixes two clear, colorless solution and mixing them produces a yellow precipitate in a clear, colorless fi

kondor19780726 [428]

Answer : Formation of yellow precipitate is the physical evidence that there has been a chemical reaction.

Explanation :

A chemical reaction happens when 2 or more substances chemically react with each other.

There are 4 evidences indicating that a chemical reaction has occurred which are mentioned below.

1. Change in color : On mixing, the reaction mixture can change color indicating that a chemical change may have occurred.

2. Formation of precipitate : A reaction in which a solid is formed on mixing 2 aqueous solutions is called as precipitation reaction. Here, the formation of solid indicates a chemical change.

ex. $AgNO_{3} (aq) + NaCl (aq) \rightarrow AgCl (s) + NaNO_{3} (aq)$

In above reaction, on mixing the solutions, a white precipitate of AgCl is formed which indicates a chemical change.

3. Evolution of gas : A chemical change also occurs when a gas is evolved on mixing 2 substances.

ex. $2HCl (aq) + Na_{2}CO_{3} (aq) \rightarrow 2NaCl (aq) + H_{2}O (l) + CO_{2} (g)$

In above reaction, CO2 gas is evolved and bubbles can be seen in the form of effervescence.

4. Change in temperature : Certain chemical reactions absorb or evolve heat. When a chemical reaction evolves heat, the temperature of the final reaction mixture increases and when it absorbs heat, the temperature decreases. This increase and decrease in temperature indicates a chemical change.

ex. $HCl (aq) + NaOH (aq) \rightarrow NaCl(aq) + H_{2}O (l)$

In above reaction, the final mixture becomes hot as the reaction releases heat. ( Exothermic)

Change in odor also indicates a chemical change.

For the given reaction, a yellow precipitate of PbI2 is getting formed.

Therefore formation of this precipitate is the physical evidence that there has been a chemical reaction.

8 0

3 years ago

Each polysaccharide tested gives different color results with the iodine test

fomenos

Iodine (iodine-potassium iodide) staining distinguishes starch ( a polysaccharide) from monosaccharides, a disaccharides and other polysaccharides. Therefore, a bluish black color is a positive test for starch, and a yellow-ish brown color ( no color change) is a negative test for starch.

4 0

3 years ago