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4 years ago

Science Questions

1 answer:

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These are 11 questions each with its jusitified answer:

1. Compounds have the same properties as the elements that form them.
A.True
B.False

Answer: False

Justification:

The properties of compounds although due to the elements and the bonds formed between them have unique properties, different to those of the elements.

That is a feature of the chemical reactions: the formation of one or more new compounds from elements are critically influenced by the bonds.

For example, think about the compound NaCl (table salt) you can see that their properties are way different from the elements Na (sodium) and Cl (chlorine) being the former highly reactive with water and the latter a strong posion. You cannot eat either Na or Cl, but certainly you can eat NaCl.

2.Electrons on the outermost layer of an atom are called valence electrons.
A.True
B.False

Anwer: TRUE.

Justification:

The valence electrons are those that participate in the formation of chemical bonds and the electrons of the outermost shell are closer to interact with other atoms and so form chemical bonds.

For a main group element, i.e. groups 1, 2, 13, 14,15, 16, 17, and 18, a valence electron can exist only in the outermost electron shell; in a transition metal, those of the groups 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12, a valence electron can also be in an inner shell

3) Compounds formed by sharing electrons are called _____ compounds.

A.) Ionic
B.) covalent
C.) positive
D.) negative
E.) neutral

Answer: option B.) covalent.

Justification:

The covalent bond is formed bu sharing a pair of electrons between atoms in a molecule.

Sharing electrons means that the atoms neither gains or loses an electron, hence no ions are formed.

The number of covalent bonds an atom can form depends upon the number of electrons that it has available for sharing.

4) Compounds formed by transferring electrons are called _____ compounds
A.) Ionic
B.) covalent
C.) positive
D.) negative
E.) neutral

Answer: option A. ionice.

Justification:

Transference of electrons means that one atom loses electrons while other atom gains electrons.

Losing and gaining electrons cause the formation of ions, which are electrically charged particles. The elecrostatic attraction between positive ions and negative ions drives to the formation of ionic compounds.

5) Elements that lose electrons will have a _____ charge.
A.) Ionic
B.) covalent
C.) positive
D.) negative
E.) neutral

Answer: option C. positive.

Justification:

Atoms are electrically neutral because they have the same number of protons (positive particles) as electrons (negative particles).

When a neutral atom loses an electron (negative particle) it will stay with more protons than electrons and leading to a net positive charge.

6) Elements that gain electrons will have a _____ charge
A.) Ionic
B.) covalent
C.) positive
D.) negative
E.) neutral

Answer: option D.) negative.

Justification:

A neutral atom has the same number of electrons as protons. Electrons are negative particles, so if an atom gains electrons it will end having more negative particles (electrons) than positive (protons) resulting in a negatively charged particle.

7) Hydrogen, an element, and Oxygen, an element, are flammable in element form.
True
False

Answer: False.

Justification.

Hydrogen is flammable but oxygen is not flammable.

Flammable is a substance that burns.

Indeed hydrogen gas (the diatomic molecule) burns easily in air, while oxygen being an oxidizer does not burn but causes other substances to oxidize, which include combustion.

8) Elements can share electrons or transfer them to another element
True
False

Answer: true.

Justification:

It is the mutual interaction between two elements which lends to the final sharing or transference of electrons. So, while Cl for example, form a ionic compound with Na (meaning that Na transferes one electron to Cl and form ions), the same Cl shares electrons with O to form covalent compounds.

9.Ionic bonds happen when electrons are given up by one atom to another
True
False

Answer: True

Justification:

When an atom gives up an electron if forms a positive ion (called cation), and when the other atoms receives the electron if forms a negative ion (called anion).

The two charged ions (cation and anion) are electrostatically attracted forming the ionic compound.

Since the number of characters exceeded the limit of 5000 characters the answers to questions 10 and 11 are in the pdf file attached.

Download pdf

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The sun's energy begins as what form of energy?

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Answer:

nuclear energy.............

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3 years ago

A 300-kg piano being held by a crane is accidentally dropped from a height of 15 meters. a. What is the speed of the piano just

FinnZ [79.3K]

Answer:

a) 17.16m/s

b) 44,145J

c) Sound the piano makes when hitting the ground, vibration of the ground, heat.

d) i) It's smaller due to the energy dissipated by the friction between air and the parachute.

ii) It stays the same, the only difference is that the dissipated energy is distributed between air resistance and the kinetic energy dissipated by the ground whent he piano hits it.

Explanation:

In order to solve this problem we must start by doing a drawing of the situation, which will help us visualize the problem better. (See attached picture).

So, in this problem we can ignore air resistance so we can say that the energy is conserved, this is the total initial energy is the same as the total final energy, so we get that:

$U_{0}+K_{0}=U_{f}+K_{f}$

When the piano is released it has an initial speed of zero, so the initial kinetic energy is zero. When the piano hits the ground it will have a height of 0m, so the final potential energy is zero as well. This will simplify our equation:

$U_{0}=K_{f}$

We know that potential energy is given by the formula:

U=mgh

and kinetic energy is given by the formula:

$K=\frac{1}{2}mv^{2}$

which can be substituted in our equation:

$mgh=\frac{1}{2}mv^{2}$

we can divide both sides of the equation into the mass of the piano, so we get:

$gh=\frac{1}{2}v^{2}$

which can be solved for the final velocity which yields:

$v=\sqrt{2gh}$

we can now substitute the data provided by the problem so we get:

$v=\sqrt{2(9.81m/s^{2})(15m)}$

which yields:

v=17.16m/s

Since energy is conserved, this means that the total dissipated energy will be the same as the potential energy, so we get that:

E=mgh

$E=(300kg)(9.81m/s^{2})(15m)$

which yields:

E=44,145J

When the piano hits the ground, the kinetic energy it had will be transformed to other types of energy, mostly vibration and heat. The vibration will turn to sound due to the movement of air created by the piano itself and the ground. And heat is created by the friction between the molecules created by the vibrations and the collition itself. So some of the indicators of this release of energy could be:

-Sound

-Vibration

-Heat.

i) The amount of inetic energy dissipated would decrease due to the friction between air and the parachute. Since air is resisting the movement of the piano, this will translate into a loss of energy, if we did an energy balance we would get that:

$U_{0}=K_{f}+E_{p}$

The total amount of energy is conserved but it will be distributed between the energy lost due to air resistance and the kinetic energy the piano has at the time it hits the ground.

ii) So the total amount of energy dissipated remains the same, the only difference is that it will be distributed between air resistance and the kinetic energy of the piano.

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4 years ago

A 60-kg rollerblader rolls 10 m down a 30? incline. When she reaches the level floor at the bottom, she applies the brakes. The

VARVARA [1.3K]

Answer:

s = 20 m

Explanation:

given,

mass of the roller blader = 60 Kg

length = 10 m

inclines at = 30°

coefficient of friction = 0.25

using conservation of energy

$\dfrac{1}{2}mu^2 = m g d sin \theta$

$u^2 = 2 g d sin30^0$

$u= \sqrt{2\times 9.8 \times 10 sin30^0}$

u = 9.89 m/s

Using second law of motion

ma =μ mg

a = μ g

a = 0.25 x 9.8

a = 2.45 m/s²

Using third equation of motion ,

v² - u² = 2 a s

0² - 9.89² = 2 x 2.45 x s

s = 20 m

the distance moved before stopping is 20 m

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4 years ago

When you whirl a can at the end of a string in a circular path, what is the direction of the force that acts on the can

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Answer:

Toward the centre of the circular path

Explanation:

The can is moved in a circular path: this means that it is moving by circular motion (uniform circular motion if its tangential speed is constant).

In order to keep a circular motion, an object must have a force that pushes it towards the centre of the circular trajectory: this force is called centripetal force, and its magnitude is given by

$F=m\frac{v^2}{r}$

where m is the mass of the object, v its tangential speed, r the radius of the trajectory. This force always points towards the centre of the circular path.

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3 years ago

Give two differences between Mass and weight

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Answer:

my opi

Explanation:

Mass is like the inside of the weight. weight is just home much it weighs

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3 years ago