All categories

3 years ago

Which of the following is evidence that

Chemistry

1 answer:

tresset_1 [31]3 years ago

4 0

Answer: c. Sugar turning black when it burns.

Explanation:

Chemical change is defined as a change in which rearrangement of atoms take place and leads to formation of new substances.

Physical change is defined as a change which leads to change in shape, size or state of the substance changes. No new substance is formed.

a) Water bubbling when it starts to boil is a physical change as it accompanies only a change in phase.

b) Detergent removing grease from a dish is a physical change as no new substance is formed.

c) Sugar turning black when it burns is a chemical change as there occurs a chemical reaction between sugar and oxygen. The oxygen in the air reacts with the sugar and the chemical bonds are broken.

d) Oil and vinegar separating in salad dressing is not a chemical change. It occurs because of difference in densities.

You might be interested in

Given the ion C2O4-2, what species would you expect to form with each of the following ions?

Ksivusya [100]

Answer:

A. K₂C₂O₄ Potassium oxalate

B. CuC₂O₄ Copper oxalate

C. Bi₂(C₂O₄)₃ Bismuth (III) oxalate

D. Pb(C₂O₄)₂ Lead (IV) oxalate

E. (NH₄)₂C₂O₄ Ammonium oxalate

F. HC₂O₄⁻ Acid oxalate

Explanation:

C₂O₄⁻² → oxalate anion

This is the conjugate base from the H₂C₂O₄ which is the oxalic acid. A weak dyprotic acid that can release 2 protons.

A. 2K⁺ + C₂O₄⁻² → K₂C₂O₄ Potassium oxalate

It can be formed by the neutralization of the acid with the base

H₂C₂O₄ + 2KOH → K₂C₂O₄ + 2H₂O

B. Cu²⁺ + C₂O₄⁻² ⇄ CuC₂O₄ ↓

This is a precipitate.

C. 2Bi³⁺ + 3C₂O₄⁻² ⇄ Bi₂(C₂O₄)₃ ↓

This is a precipitate.

D. Pb⁴⁺ + 2C₂O₄⁻² ⇄ Pb(C₂O₄)₂ ↓

This is a precipitate.

E. 2NH₄⁺ + C₂O₄⁻² ⇄ (NH₄)₂C₂O₄ ↓

This is a precipitate.

F. This is the conjugate strong base, for the weak acid

H⁺ + C₂O₄⁻² ⇄ HC₂O₄⁻

HC₂O₄⁻ + H₂O ⇄ C₂O₄⁻² + H₃O⁺ Ka

HC₂O₄⁻ + H₂O ⇄ H₂C₂O₄ + OH⁻ Kb

HC₂O₄⁻ is an amphoteric compound

6 0

3 years ago

How many moles of oxygen atoms are in 7.9E-1 moles of CO_2

Ilya [14]

Answer:

The number of moles of O atom in $(7.9\times10^{-1})$ mol of $CO_{2}$ = 1.6

Explanation:

1 molecule of $CO_{2}$ contains 2 atoms of O

So, $(6.023\times 10^{23})$ molecules of $CO_{2}$ contains $(2\times6.023\times10^{23})$ atoms of O.

We know that 1 mol of an atom/molecule/ion represents $6.023\times10^{23}$ numbers of atoms/molecules/ions respectively.

So, $(6.023\times 10^{23})$ molecules of $CO_{2}$ is equal to 1 mol of $CO_{2}$ .

$(2\times6.023\times10^{23})$ atoms of O is equal to 2 moles of O atom.

Hence, 1 mol of $CO_{2}$ contains 2 moles of O atom.

Therefore, $(7.9\times10^{-1})$ mol of $CO_{2}$ contains $(2\times7.9\times10^{-1})$ moles of O atom or 1.6 moles of O atom.

3 0

3 years ago

Explain how scientist learned about the magnetic poles of the Earth.

MatroZZZ [7]

Answer:

They learned because they keeped studying they would never give up and if they found something new or interesting they may have just studied it more.

Explanation:

3 0

3 years ago

Read 2 more answers

HELP PLEASE! <br> Picture for question provided

BartSMP [9]

Answer:

Explanation:

The first one is CrO. The Chromium has the same charge as the oxygen so mol numbers are dropped.

The Second one is CrO2 The two oxygens have a charge of 2(-2) = -4. To balance this, the Chromium must have a charge of +4 Cr(Iv)O2

The third one is can be set up like this

Cr + 3(-2) = 0

Cr - 6 = 0

Cr = 6

Therefore the formula is Cr(vi)O3

The last one is a bit tricky. Follow this carefully. There are 2 Crs and 3Os.

The formula looks like this

2Cr + 3(-2) = 0

2Cr - 6 = 0

2Cr = 6

Cr = 3

The formula is Cr(iii)2 O3

5 0

3 years ago

Microwave radiation has a wavelength on the order of 1.0 cm. Calculate the frequency and the energy of a single photon of this r

denis23 [38]

Answer :

(1) The frequency of photon is, $3\times 10^{10}Hz$

(2) The energy of a single photon of this radiation is $1.988\times 10^{-23}J/photon$

(3) The energy of an Avogadro's number of photons of this radiation is, 11.97 J/mol

Explanation : Given,

Wavelength of photon = $1.0cm=0.01m$ (1 m = 100 cm)

(1) Now we have to calculate the frequency of photon.

Formula used :

$\nu=\frac{c}{\lambda}$

where,

$\nu$ = frequency of photon

$\lambda$ = wavelength of photon

c = speed of light = $3\times 10^8m/s$

Now put all the given values in the above formula, we get:

$\nu=\frac{3\times 10^8m/s}{0.01m}$

$\nu=3\times 10^{10}s^{-1}=3\times 10^{10}Hz$ $(1Hz=1s^{-1})$

The frequency of photon is, $3\times 10^{10}Hz$

(2) Now we have to calculate the energy of photon.

Formula used :

$E=h\times \nu$

where,

$\nu$ = frequency of photon

h = Planck's constant = $6.626\times 10^{-34}Js$

Now put all the given values in the above formula, we get:

$E=(6.626\times 10^{-34}Js)\times (3\times 10^{10}s^{-1})$

$E=1.988\times 10^{-23}J/photon$

The energy of a single photon of this radiation is $1.988\times 10^{-23}J/photon$

(3) Now we have to calculate the energy in J/mol.

$E=1.988\times 10^{-23}J/photon$

$E=(1.988\times 10^{-23}J/photon)\times (6.022\times 10^{23}photon/mol)$

$E=11.97J/mol$

The energy of an Avogadro's number of photons of this radiation is, 11.97 J/mol

3 0

3 years ago

Read 2 more answers