CHEMISTRY HIGH SCHOOL

The chemical formula for emerald is Be3Al2(SiO3)6. An emerald can be described asa pure substance because it is a compound.
a pure substance because it is an element.
an impure substance because it is chemically combined.
an impure substance because it is a mixture.

Answers

Answer 1
Answer:

Answer is: a pure substance because it is a compound.

Pure substance is made of only one type of atom or only one type of molecule, it has definite and constant composition with distinct chemical properties.

Emerald (beryl) is chemical compound (beryllium aluminium cyclosilicate) with the chemical formula Be₃Al₂(SiO₃)₆.  Pure beryl is colorless.
Answer 2
Answer:

An emerald can be described as an impure substance because it is a mixture. Therefore, option D is correct.

The chemical formula for emerald is Be₃Al₂(SiO₃)₆, indicating that it is a compound composed of beryllium (Be), aluminum (Al), and silicon (Si) atoms bonded to oxygen (O) atoms.

However, emeralds can also contain impurities or trace elements such as chromium (Cr) or vanadium (V), which give them their characteristic green color.

These impurities or trace elements are present in small amounts and are incorporated into the crystal structure of the emerald.

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What is the half life of a radioisotope if 25.0 grams of anoriginal 200.-gram sample of the isotope remainsunchanged after 11.46 days?3) 11.46 d1) 2.87 d4) 34.38 d2) 3.82 d

Answers

Half-life is the amount of time, in days or years( most common) a certain substance disintegrate half of it's content.
We are given the initial (Ao) and final (A) amount of the substance. The time passed (T) is also given and we are asked to find the half-life (t). We use the equation below:

A=Aoe^(-ln2/t)T
25=200e^(-ln2/t)(11.46)
Solve for t
Answer: 3.82 days

Calculate the number of molecules in 210 grams of H2O

Answers

The number of molecules in 210 grams of H₂O is 72.48 x 10²⁴.

What are moles?

The mole is a SI unit of measurement that is used to calculate the quantity of any substance. The number of models of any substance can be calculated by dividing the mass by the molar mass of the substance or compound.

Mole = mass / molar mass

Given the mass of wateris 210 grams

The molar mass of water is 18.01g/mole

The mass and the molar mass will be divided.

210 / 18.01g = 11.653 mole

Now, here 1 mole is 6.22 x 10²³ molecules, so the 6.22 x 10²³ will be multiplied by the 11.653 to get the molecules of 210-gram water.

1 mole has 6.22 x 10²³  molecules

11.653 mole x 6.22 x 10²³ = 72.48 x 10²⁴

Thus, the number of molecules of H₂O is 72.48 x 10²⁴.

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H2O=18.01g/mole. 210g divided by 18.01g/mole=11.653mole. 1 mole has 6.22x10^23 molecules. So there is 11.653x(6.22x10^23) molecules. Just multiply 11.653 by 6.22. Then put it as answerx10^23 molecules

Which statement is true because of newtons second law ?a)when the net force on an object increases, the objects acceleration decreases
b)when the net force on an object decreases ,the objects acceleration increases
c)when the net force on an object decreases, the acceleration doesnt change
d)when the net force on an object decreases, the objects acceleration decreases

Answers

Newton's second law, by definition, states that,  The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. Therefore, based on the given options above, the correct answer would be option D: when the net force on an object decreases, the objects acceleration decreases.

d. when the net force on an object decreases, the objects acceleration decreases


i took the test and got it right

Which element has an atom in the ground state with a total of three valence electrons

Answers

1) Aluminum
2) Lithium
3) Phosphorus

A radioactive isotope has a half-life of 10 minutes.At the start of an experiment, the activity of a sample of this isotope was 800 counts
per second after allowing for background radiation.
Calculate how long it would be before the activity fell from 800 counts per second to
200 counts per second.

Answers

Answer: The time for activity to fell from 800 counts per second to 200 counts per second is 20 minutes

Explanation:

Expression for rate law for first order kinetics is given by:

t=(2.303)/(k)\log(a)/(a-x)

where,

k = rate constant

t = age of sample

a = let initial amount of the reactant

a - x = amount left after decay process  

a) for finding the rate constant:

Half life is the amount of time taken by a radioactive material to decay to half of its original value.

t_{(1)/(2)}=(0.693)/(k)

k=(0.693)/(10min)=0.0693min^(-1)

b) for activity to fell from 800 counts per second to 200 counts per second.

t=(2.303)/(0.0693)\log(800)/(200)

t=20minutes

The time for activity to fell from 800 counts per second to 200 counts per second is 20 minutes

Final answer:

The half-life of the given radioactive isotope is 10 minutes. The activity of the isotope falls to half its initial value every 10 minutes. Hence, it would take 20 minutes for the activity to fall from 800 counts per second to 200 counts per second.

Explanation:

The process you're describing relates to the concept of radioactive decay, which is a fundamental principle in nuclear physics. In this case, we're dealing with what's known as a half-life. The half-life of a radioactive isotope is the time it takes for half of the isotope in a sample to decay.

In this scenario, the radioactive isotope has a half-life of 10 minutes and it starts with a sample activity of 800 counts per second. According to the nature of half-life, it will reduce to half of its initial counts, 400 counts per seconds in 10 minutes. Importantly, another 10 minutes would be required for the number of counts to halve again to 200 counts per second.

Therefore, it would take 20 minutes for the activity to fall from 800 counts per second to 200 counts per second.

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A solution of salt (molar mass 90 g mol-1) in water has a density of 1.29 g/mL. The concentration of the salt is 35% by mass.a. Calculate the molality of the solution.

b. Calculate the molarity of the solution.

c. Calculate the mole fraction of the salt in the solution.

Answers

The molarity of the solution is 5.018 mol/L and molality of the solution 5.9846 mol/kg.

 

Assume 100 g of solution the salt concentration- 35 % and water will be 65 %.    

So,  

mass of salt = 35 g  

mass of water = 65 g  

Number of moles,  

\bold {moles = \frac {mass} { molar\ mass}}

So,    

moles of salt = 35 g / 90 (g/mol) = 0.389 mole  

moles of water = 65 / 18 = 3.6111 mole  

 

Volume of solution,

\bold {volume =\frac { mass } {density }}  

volume = 100 g / ( 1.29 g/ml)  

volume of solution = 77.52 ml = 0.07752 L  

 

a)

\bold {Molality = \frac {moles\ of \salt} { mass\ of\ water (kg)}}  

molality = 0.389 mol / 0.065 kg  

molality = 5.9846 mol/kg  

b)  

molarity = moles of salt / volume of solution (L)

molarity = 0.389 mol / 0.07752 L  

molarity = 5.018 mol/L  

c)    

 mole fraction of salt = moles of salt / total moles  

mole fraction of salt = 0.389 mol / ( 0.389 + 3.6111)  

mole fraction of salt = 0.09725

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Answer:

a) 5.9846 mol/kg

b) 5.018 mol/L

c)0.09725

Explanation:

consider 100 g of solution

now

since the salt is 35 % , water will be 65 %

now

mass of salt = 35 g

mass of water = 65 g

we know that

moles = mass / molar mass

so

moles of salt = 35 g / 90 (g/mol) = 0.389 mol

moles of water = 65 / 18 = 3.6111 mol

now

volume of solution = mass of solution / density of solution

volume of solution = 100 g / ( 1.29 g/ml)

volume of solution = 77.52 ml

volume of solution = 0.07752 L

a)molality = moles of salt / mass of water (kg)

molality = 0.389 mol / 0.065 kg

molality = 5.9846 mol/kg

b)

molarity = moles of salt / volume of solution (L)

molarity = 0.389 mol / 0.07752 L

molarity = 5.018 mol/L

c)

now

total moles in the solution = moles of salt + moles of water

total moles in the solution = 0.389 + 3.6111

total moles in the solution = 4 mol

now

mole fraction of salt = moles of salt / total moles

mole fraction of salt = 0.389 mol / 4 mol

mole fraction of salt = 0.09725
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