CHEMISTRY HIGH SCHOOL

What is the SI base unit for time?

Answers

Answer 1

Answer: The "second" is the SI base unit of time.

Answer 2

Answer:

Answer:

Second

Explanation:

i took the test

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What is the molarity of 0.50 g of Na dissolved in a 1.5 L solution?

Answers

Answer : The molarity of solution is, 0.0145 mole/L

Solution : Given,

Mass of solute, Na= 0.50 g

Volume of solution = 1.5 L

Molar mass of Na= 23 g/mole

Molarity : It is defined as the number of moles of solute present in the one liter of solution.

Formula used :

$Molarity=(w_b)/(M_b* V)$

where,

$w_b$ = mass of solute, Na

V = volume of solution in liters

$M_b$ = molar mass of solute, Na

Now put all the given values in the above formula, we get the molarity of a solution.

$Molarity=(0.50g)/(23g/mole* 1.5L)=0.0145mole/L$

Therefore, the molarity of solution is, 0.0145 mole/L

Molar mass Na = 23.0 g/mol

1 mole Na ------- 23.0 g
? mole Na ------ 0.50 g

moles = 0.50 * 1 / 23.0

moles = 0.50 / 23.0

= 0.0217 moles of Na

Molarity = number of moles / liters solution

M = 0.0217 / 1.5

= 0.014467 M

hope this helps!

Formula for the compound that contains Mg2+ and O2-

Answers

Answer:

MgO.

Explanation:

charges of both satisfy one another (balanced) -- producing a compound MgO.

A student tested a sample of carbon (C) by combining it with water. There was no reaction between the carbon and water. The student concluded that carbon must be a group 18 element, since it was unreactive. State whether you agree with the student's reasoning, and explain why or why not?

Answers

I disagree. Carbon is not a group 18 element. This is incorrect because elements closer to the top of the group are less reactive than those at the bottom of the group. Group 18 elements are noble gases and carbon, a group 14 element, is a non metal.

Why it is that evaporation causes cooling,but boiling causes heating?

Answers

in evaporation due to internal heat, kinetic energy of molecules increases and they come to the top and take out that heat with them when they evaporate thus causes cooling
in boiling as heat is given to the molecules so their kinetic energy increases and they start vibrating with great energy and thus causes heating

During evaporation, particles which have a high kinetic energy come out of the body by gaining heat due to which there is a cooling effect on the particle of the body itself. that is why, evaporation causes cooling. For example: sweating

The concentration of gallium in silicon is 5.0 × 10−7 at%. What is the concentration in kilograms of gallium per cubic meter?

Answers

The concentration of gallium in kilograms per cubic meter is equal to the calculated mass of gallium per cubic meter.

To determine the concentration of gallium in kilograms per cubic meter, we need to convert the concentration from atomic percent (at%) to kilograms per cubic meter.

The atomic fraction is the ratio of the number of gallium atoms to the total number of atoms in the silicon-gallium mixture.

We need to know the atomic masses of gallium and silicon. The atomic mass of gallium is 69.72 g/mol, and the atomic mass of silicon is 28.09 g/mol.

The atomic fraction of gallium can be calculated using the formula:

Atomic fraction of gallium = (Concentration of gallium in at%) / (Atomic mass of gallium) / [(Concentration of gallium in at%) / (Atomic mass of gallium) + (Concentration of silicon in at%) / (Atomic mass of silicon)]

Plugging in the given values:

Atomic fraction of gallium = ( $5.0 * 10^(-7)$ %) / (69.72 g/mol) / [( $5.0 * 10^(-7)$ at%) / (69.72 g/mol) + (100 - $5.0 * 10^(-7)$ ) at% / (28.09 g/mol)]

Now, let's convert the atomic fraction to the number of gallium atoms per cubic meter. We can use Avogadro's number, to make this conversion.

Number of gallium atoms per cubic meter = Atomic fraction of gallium × Avogadro's number.

Mass of gallium per cubic meter = Number of gallium atoms per cubic meter × (Atomic mass of gallium / 1000)

Therefore, the concentration of gallium in kilograms per cubic meter is equal to the calculated mass of gallium per cubic meter.

Learn more about Concentration here;

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Final answer:

The concentration of gallium in kilograms per cubic meter can be calculated using the atomic mass of gallium and Avogadro's number.

Explanation:

To calculate the concentration of gallium in kilograms per cubic meter, we can use the atomic mass of gallium and Avogadro's number. The concentration in kilograms per cubic meter can be found using the formula:

Concentration (kg/m³) = Concentration (% by mass) x Density (g/cm³) x Atomic Mass (g/mol) / 1000 x Avogadro's Number

First, convert the concentration from at% (atomic percent) to % by mass. Since gallium has an atomic mass of 69.7 g/mol, we can use this value to find the concentration in kilograms per cubic meter.

Learn more about concentration of gallium here:

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Chemical changes ________ involve the breaking and making of chemical bonds.A) Always
B) Never
C) Sometimes

Fill in the blank

Answers

The correct answer that would best complete the given statement above would be option A. Chemical changes ALWAYS involve the breaking and making of chemical bonds. When there is chemical change, a new compound is being formed. If a new compound is not formed, then it is not considered as a chemical change. When a new compound is formed, therefore, there is the breaking and making of chemical bonds. Hope this helps.

Answer:

A: Always.

Explanation:

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A chemist who is performing this reaction starts with 160.1 g of NH4NO3. The molar mass of NH4NO3 is 80.03 g/mol; the molar mass of water (H2O) is 18.01 g/mol. What mass, in grams, of H2O is produced?