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4 years ago

Which phrase describes an al atom?

1 answer:

5 0

Answer:
None of the given options describe any atom. The phrase which describe an atom is "a positively charged nucleus surrounded by negatively charged electrons".

Explanation:
Atom is a smallest indivisible particle which is made up of many sub particles. The main sub particles are Protons, Neutrons and Electrons. Protons are positively charged, neutrons doesn't carry any charge hence neutral and electrons are negatively charged. Protons and neutrons are present in nucleus, therefore making the nucleus positively charged, while, electrons revolve around the nucleus in orbit hence being negatively charged particles surrounds the positively charged nucleus.

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in Analytical chemistry laboratory. Nickle(ppm)in water sample estimated by two different students was as ,student 1 (25 24 24 2

frosja888 [35]

Answer:

Answers are in the explanation

Explanation:

Precision and accuracy are both statistical concepts. Precision is about how close are the measured values to each other. Accuracy is closeness of the measured values to a specific value or reference value.

There are many ways to calculate precision and accuracy, one is stimating precision as Relative Uncertainty and accuracy as Relative Error.

Formulas are:

Relative Uncertainty: Standard desviation / Measured value.

Relative Error: Measured Value - Expected Value / Expected value

Measured value is the aveage of the values.

For student 1:

Mean = 25

Standard desviation = 1.5275

Relative Uncertainty: 1.5275 / 25

Relative Uncertainty: 0.061

Relative Error: 25 - 20 / 20

Relative Error: 0.25

For student 2:

Mean = 24.5

Standard desviation = 0.5477

Relative Uncertainty: 0.5477 / 24.5

Relative Uncertainty: 0.02

Relative Error: 24.5 - 20 / 20

Relative Error: 0.225

As the student 2 has a low Relative error and uncertainty, you can say student 2 is more accurate and precise

6 0

4 years ago

A 100-watt light bulb radiates energy at a rate of 100 J/s. (The watt, a unit of power or energy over time, is defined as 1 J/s.

Semmy [17]

Answer

2.7956 * 10^19 photons

Givens

Wavelength = λ = 525 * 10^-9 meters [1 nmeter = 1*10^-9 meters]
c = 3 * 10^8 meters
E = ???
W = 100 watts
t = 1 second
h= plank's Constant = 6.26 * 10^-34 J*s

Formula

E = h * c / λ

W = E / t

Solution

E = 6.26 * 10^-34 j*s * 3 * 10^8 m/s /525 * 10^-9 (m)

The meters cancel out. So do the seconds. You are left with Joules as you should be.

E = 3.577 * 10^-18 Joules

What you have found is the energy of 1 photon.

Now you have to find the Joules from the watts.

W = E/t

100 * 1 second = 100 joules

1 photon contains 3.577 * 10 ^ - 18 Joules

x photon = 100 joules

1/x = 3.577 * 10^-18 / 100 Cross multiply

100 = 3.577 * 10 ^ - 18 * x Divide both sides by 3.577 * 10 ^ - 18

100/3.577 * 10 ^ - 18 = 3.577 * 10 ^ - 18x / 3.577 * 10 ^ - 18

2.7956 * 10^19 photons = x

7 0

3 years ago

How many grams of O2 are needed to react with 18.2 g of NH3?

erastova [34]

Answer:

44 g oxygen are needed.

Explanation:

Given data:

Mass of oxygen needed = ?

Mass of ammonia = 18.2 g

Solution:

Chemical equation:

4NH₃ + 5O₂ → 4NO + 6H₂O

Now we will calculate the number of moles of ammonia:

Number of moles = mass/molar mass

Number of moles = 18.2 g/ 17 g/mol

Number of moles = 1.1 mol

Now we will compare the moles of ammonia with oxygen from balance chemical equation.

NH₃ : O₂

4 : 5

1.1 : 5/4×1.1 = 1.375 mol

Mass of oxygen needed:

Mass = number of moles × molar mass

Mass = 1.375 mol × 32 g/mol

Mass = 44 g

4 0

3 years ago

Which is an example of chemical weathering?

kobusy [5.1K]

Answer:

b. the layer of oxide formed on statues made of metal

Explanation:

Chemical weathering is a process whereby rocks are disintegrated or weathered causing a chemical reaction thereby leading to change in the parent rock constituents .

In chemical weathering a new substance is usually formed after the weathering takes place.

From the question the layer of statue made by metal will likely form oxides of those metals. Example Silver will react with oxygen to form an entirely new substance like silver(i)oxide.

7 0

3 years ago

13. During photosynthesis, carbon dioxide and water combine according to the general

yKpoI14uk [10]

C is the answer hope the answer is right

5 0

3 years ago