#15 need help don’t understand

Answer:

The answer is C!

Explanation:

Hope it helps

Answer D

Explanation: did the quiz ψ(｀∇´)ψ

Answer:

Adding fluoride to the water supply reduces the incidence of tooth decay. Fluoride protects teeth from decay by demineralization and remineralization. Too much fluoride can lead to dental fluorosis or skeletal fluorosis, which can damage bones and joints.

Explanation:

N/A

Answer:

0.0225 M

Explanation:

In one liter of this solution, there are 45 mEq of Ca⁺².

1 mEq of Ca⁺² is equal to 20 mg of Ca⁺. We know this by dividing its molar mass (40) by the charge of the ion (2).

Meaning that 45 mEq of Ca⁺² is equal to (45 * 20) 900 mg of Ca⁺².

Now we convert 900 mg of Ca⁺² into moles, using its molar mass:

Finally we calculate the molarity of the solution:

Answer:

The stratosphere

Explanation:

Answer: CuSO4 (aq)+ Zn (s) → Cu (s) + ZnSO4(aq)

Explanation: do you mean copper II sulphate CuSO4?

Answer: The name of the super continent that existed millions of years ago.

Explanation:

Our continents as they exist today were once joined together into a super continent known as Pangea. Over the millennia, the land masses broke off and drifted away creating the location of the continents we know today.

(つ ^‿^ )つ Hey there!

Answer → Is the second answer, The name of the super continent that existed millions of years ago.  

✨Hope this helps!✨

Answer:

2 is correct

Explanation:

My friend for you this answer

Answer:

The empty space between the atomic cloud of an atom and its nucleus is just that: empty space, or vacuum. ... Electrons are thus 'spread out' quite a bit in their orbits about the nucleus. In fact, the wave-functions for electrons in s-orbitals about a nucleus actually extend all the way down into the nucleus itself.

Answer:

As you cool a matter to absolute zero, their kinetic energy reduces significantly and the molecules slows down and begins to aggregate together. ... As heat is added, the molecules gain more kinetic energy. This shown in their increase motion. When heat is withdrawn, the particles slows down hope this helped

Answer:

The climate has been caused by many natural factors including changes in the sun emissions from volcanoes variations in Earth's orbit and levels of carbon dioxide. Global climate change has typically occured very slowly over thousands or millions of years .The three causes of the Earth's climate are

these are the causes of the Earth's climate.

Climate is a average weather in a given area for a long period of time is called a climate

maybe this might help ur question

Answer:

Lake pontchartrain

Explanation:

Answer:

The couch will not move because the people are not working together. Maybe if they call someone to help they can make some progress.

Answer:

26.8 °C

Explanation:

Step 1: Given and required data

Step 2: Calculate the final temperature of the water

We will use the following expression.

Q = c × m × (T₂ - T₁)

T₂ = 2100 J/(4.184 J/g.°C) × 155 g + 23.6 °C = 26.8 °C

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Answer:

simple chemistry experiment—adding baking soda to vinegar—seems to challenge the law of conservation of mass.

Some of the mass escaped from the test tube as a gas before it was massed. Hence option C is correct.

Experiment is defined as a process used to confirm or deny a hypothesis, as well as assess the likelihood or effectiveness of a previously untested idea. Additionally, experiments are used by researchers to confirm or refute new or current theories. The structure or mathematical form of a theory can be hinted at by an experiment, and it can also provide proof that the entities involved in our theories actually exist.

Something new is created when vinegar and baking soda are combined. Carbon dioxide gas soon foams up in the mixture. All of the baking soda can be made to react and dissolve into the vinegar solution if enough vinegar is utilized.

Thus, some of the mass escaped from the test tube as a gas before it was massed. Hence option C is correct.

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Answer:

32.8%

Explanation:

All of the Pb⁺² species precipitated as lead(II) cromate, PbCrO₄ (we know this as excess K₂CrO₄ was used).

First we convert 0.130 g of PbCrO₄ into moles, using its molar mass:

There's 1 Pb⁺² mol per PbCrO₄ mol, so in total 4.02x10⁻⁴ moles of Pb⁺² were in the ethanoate sample.

We convert those 4.02x10⁻⁴ moles of Pb into grams:

Finally we calculate the percentage composition of Pb:

The item that is significantly made up of one or more molecules is hydrogen. Thus, the correct option for this question is B.

A molecule may be defined as a group of one or more atoms that are held together by numerous chemical bonds. It is the smallest particle of a substance that has all sorts of physical and chemical properties of that substance.

Among the given options, gold and neon are the elements, while salt is a compound. Hydrogen is a gas of diatomic molecules bearing the formula H2. It is colorless, tasteless, odorless, non-toxic, and highly combustible. Hydrogen in its molecular form is more common.

A hydrogen molecule is one of the simplest possible molecules which significantly consists of two protons and two electrons. These protons and electrons are remarkably held together by electrostatic forces.

Therefore, the item that is significantly made up of one or more molecules is hydrogen. Thus, the correct option for this question is B.

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Answer: 9.46

Explanation: in LiOH solution concentration of OH- ions is 2.88·10^-5 M

And pOH = -log( 2.88·10^-5 M) = 4.54. Because PH + pOH = 14.00

Then pH = 14-4.54

Answer:

The fourth one- bromo trifluoro methane

Explanation:

Answer:

D

Explanation:

I believe the answer is the 4th option, bromo-trifluoro-methane

The gas that has the least collisions between its particle is helium at 20° C. The correct option is A.

Collision is a term used when two particles or object collides or clash and there is an exchange or transformation of energy between them. When a collision happens, the force is exerted on each other.

Helium is the second most abundant element present in the atmosphere. It is the lightest gas and its particle collides when there is an increase in the temperature.

Thus, the correct option is A. Helium at 20° C., regarding the collision of particles between its particles.

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Answer:

The main universal indicator is in the form of a solution and are thymol blue , methyl red , bromothymol blue and phenolphthalein this mixture is important because each component loses or gains protons depending upon the acidity of the solution being tested .

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Answer:

0.3529moles

Explanation:

no of moles =mass ÷molar mass

molar mass =17+17

=34

12÷34

=0.3529moles

According to the mole concept, the number of moles of molecules in a 12.0-gram sample of Cl₂ is equal to 0.169  moles.

Mole is defined as the unit of amount of substance . It is the quantity measure of amount of substance of how many elementary particles are present in a given substance.

It is defined as exactly 6.022×10²³ elementary entities. The elementary entity can be a molecule, atom ion depending on the type of substance. Amount of elementary entities in a mole is called as Avogadro's number.

It is widely used in chemistry as a suitable way for expressing amounts of reactants and products.For the practical purposes, mass of one mole of compound in grams is approximately equal to mass of one molecule of compound measured in Daltons. Molar mass has units of gram per mole . In case of molecules, where molar mass  in grams present in one mole  of atoms is its atomic mass.Number of moles is mass/molar mass= 12/70.90=0.169 moles.

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Answer: x + 10y - 10z is the answer

Explanation:

Answer: Cut the card borad

Explanation:

Answer:

CH

Explanation:

Polystyrene is composed only by C and H.

We can calculate the number of C moles contained in the original sample mass (0.00215 g), using the produced mass of CO₂:

As 1.65x10⁻⁴ moles of CO₂ were produced, in the polystyrene sample there were 1.65x10⁻⁴ moles of C.

Now we calculate how many moles of H₂O were produced:

The number of H moles produced is double the amount of H₂O moles, so in the polystyrene sample there were 1.64x10⁻⁴ moles of H.

The number of C and H moles are the same, this means the empirical formula is CH.

Answer:

phase change always has two phases in contact during the change. melting => solid & liquid; evaporation (boiling) => liquid & vapor. If only one phase is present, then phase change is not occurring. Also, when two phases are in contact, no temperature changes occur. Only the pure phase demonstrates temperature change when measured. Example, when ice is added to water, at thermal equilibrium (temp = 0°C) the water temp will not continue to change. Only when all the ice has melted will the water temperature demonstrate a measured temperature change.

Explanation: