Is kcal energy? Thanks!

The element lanthanum has two stable isotopes, lanthanum-138 with an atomic mass of 137.9 AMU and lanthanum-139 with an atomic m

dmitriy555 [2]

Answer:

A. there is an isotope of lanthanum with an atomic mass of 138.9

Explanation:

By knowing the different atomic masses of both Lanthanum atoms, we can not tell anything about their occurence in nature. Therefore, all the last three options are incorrect. Because, the atomic mass does not tell anything about the availability or natural abundance of an element.

Now, the isotopes of an element are those elements, which have same number of electrons and protons as the original element, but different number of neutrons. Therefore, they have same atomic number but, different atomic weight or atomic masses.

Hence, by looking at an elements having same atomic number, but different atomic masses, we can identify them as isotopes.

Thus, the correct option is:

A. there is an isotope of lanthanum with an atomic mass of 138.9.

7 0

3 years ago

What is the percent of hydrogen peroxide in the solution when 5.02g of H2O2 solution reacts to produce 0.153g of H2O2? 2H2O2 (l)

Murljashka [212]

Given:

Mass of H2O2 solution = 5.02 g

Mass of H2O2 = 0.153 g

To determine:

The % H2O2 in solution

Explanation:

Chemical reaction-

2H2O2(l) → 2H2O(l) + O2(g)

Mass % of a substance in a solution = (Mass of the substance/Mass of solution) * 100

In this case

% H2O2 = (Mass H2O2/Mass of solution)* 100 = (0.153/5.02)*100 = 3.05%

Ans: % H2O2 in the solution = 3.05%

5 0

3 years ago

The correct name for hno2 is ________. nitrous acid hyponitrous acid nitric acid pernitric acid hydrogen nitrate

balu736 [363]

Nitrous Acid.

Hyponitrous acid: H2N2O2

Nitric acid: HNO3

Pernitric acid: HNO

4 0

2 years ago

In the reaction MnO₂ + 4HCI MnCl₂ + 2H₂O + Cl₂, which species is reduced?

Triss [41]

Answer:

4 HCl (aq) + MnO2 (s) → MnCl2 (aq) + Cl2 (g) + 2 H2O (l)

This is an oxidation-reduction (redox) reaction:

MnIV + 2 e- → MnII (reduction)

2 Cl-I - 2 e- → 2 Cl0 (oxidation)

MnO2 is an oxidizing agent, HCl is a reducing agent.

Reactants:

HCl – Chlorane, Hydrogen chloride

Other names: Hydrochloric acid
Appearance: Colorless, transparent liquid, fumes in air if concentrated; Colorless gas; Colourless compressed liquefied gas with pungent odour; Colorless to slightly yellow gas with a pungent, irritating odor. [Note: Shipped as a liquefied compressed gas.]

MnO2 – Manganese oxide, Manganese(IV) oxide

Other names: Manganese dioxide, Pyrolusite, Hyperoxide of manganese

Appearance: Brown-black solid Black-to-brown powder

Products:

MnCl2 – Manganese(II) chloride, Manganese dichloride

Other names: Manganous chloride, Manganous dichloride Manganese(II) chloride (1:2)

Appearance: Pink solid (tetrahydrate)

Cl2

Names: Chlorine, Molecular chlorine

Appearance: Greenish-yellow compressed liquefied gas with pungent odour ; Greenish-yellow gas with a pungent, irritating odor. [Note: Shipped as a liquefied compressed gas.]

H2O – Water, oxidane

Other names: Water (H2O) Hydrogen hydroxide (HH or HOH) Hydrogen oxide

Appearance: White crystalline solid, almost colorless liquid with a hint of blue, colorless gas

Explanation:

6 0

2 years ago

Read 2 more answers

Predict the shape of the molecule.

balandron [24]

Answer:

B.) trigonal bipyramidal

Explanation:

A.) is incorrect. In octahedral molecules, the central atom is bonded to six other atoms.

B.) is correct. In trigonal bipyramidal structures, the central atom is bonded to five other atoms.

C.) is incorrect. In tetrahedral molecules, the central atom is bonded to four other atoms.

D.) is incorrect. There is not such thing as a pyramidal molecular shape. This term is most likely referring to the shape, trigonal pyramidal. However, this is still incorrect. In trigonal pyramidal molecules, the central atom is bonded to three other atoms and a lone pair of electrons.

7 0

1 year ago