MULTIPLE CHOICE. Choose the one alternative that best completes the statement or

Question

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) A compound that is composed of carbon, hydrogen, and oxygen contains 70.6% C. 5.9% H and 23.5% O by mass. The molecular weight of the compound is 136 amu. What is the molecular formula? A) C4H40 B) C9H120 C) C5H602 D) C8H40 E) C8H802 2) The correct name for SrO is A) strontium oxide B) stron C) strontium hydroxide D) strontium dioxide E) strontium peroxide tium monoxide 3) Elements in Group 2A are known as the- A) halogens B) alkali metals C) noble gases D) chalcogens E) alkaline earth metals

Explanation / Answer

1. E) C8H8O2.

3 answers · Chemistry

Best Answer

First you need to work out the empirical formula of the compound:

It contains 70.6% carbon, 5.9% hydrogen and 23.5% oxygen.

So - divide these percentages by the molar mass of the elements to get a number of moles for each substance.

Carbon: 70.6/12 = 5.88333333
Hydrogen: 5.9/1 = 5.9
Oxygen: 23.5/16 = 1.46875

Now arrange these in a ratio as follows:
C:H:O
5.883333 : 5.9 : 1.46875

Now try and make the ratio into whole numbers (divide through by the smallest number) as follows:

4:4:1

Therefore, your empirical formula is C4H4O

Then calculate the molar mass of that molecule:
(4x12) + (4x1) + (1x16) = 48 + 4 + 16 = 68

Since, 68 goes into 136 twice, your molecular formula is : C8h8o2.

2.A) Strontium oxide

Strontium oxide or SrO, is formed when strontium reacts with oxygen. Strontium Oxide is created when these chemical reaction occurs: SrO + H2O -----> Sr(OH)2.Strontium Oxide is a highly insoluble thermally stable Strontium source suitable for glass, optic and ceramic applications. There are some major characteristics of strontium Oxide are:Solubility in water: reacts, forms Sr(OH)2

Crystal structure: Halite (cubic), cF8

Melting point: 2530°C; 2665°C

Boiling point: 3000°C

3. E) Alkaline Earth Metals

The alkaline earth metals are six chemical elements in group 2 of the periodic table. They are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).They are reactive, electropositive, divalent metals, and form basic oxides which react with water to form comparatively insoluble hydroxides.The alkaline-earth elements are highly metallic and are good conductors of Electricity.

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