Answer:
You need to measure 120.9132 grams of MgO and add to 1 liter of distilled water in a beaker.
Explanation:
Capital M stands for molarity, or moles/liter. So 3 M MgO means 3 moles per liter of MgO.
1 L × 
= 3 moles MgO
This means you need to measure 3 moles MgO to put into 1 Liter of water.
But you don't know how much that is, so you need to convert moles to grams.
First you need to find how many grams are in 1 mole of MgO.
You can search the molar mass of MgO online to get: 40.3044 g
But if you don't have the internet, use the periodic table to add the masses of Mg and O: 24.305 g + 15.999 g = 40.3044 g
Then write the fraction so that the units cancel out, so you get grams by itself on the top of the fraction.
1 L × × 
= 120.9132 g MgO
You need to measure 120.9132 grams of MgO and add to 1 liter of distilled water.
<h3>
Answer:</h3>
12.4 g N₂O₂
<h3>
General Formulas and Concepts:</h3>
<u>Chemistry</u>
<u>Atomic Structure</u>
- Reading a Periodic Table
- Moles
- Avogadro's Number - 6.022 × 10²³ atoms, molecules, formula units, etc.
<u>Stoichiometry</u>
- Using Dimensional Analysis
<h3>
Explanation:</h3>
<u>Step 1: Define</u>
[Given] 1.24 × 10²³ molecules N₂O₂
[Solve] grams N₂O₂
<u>Step 2: Identify Conversions</u>
Avogadro's Number
[PT] Molar Mass of N - 14.01 g/mol
[PT] Molar Mass of O - 16.00 g/mol
Molar Mass of N₂O₂ - 2(14.01) + 2(16.00) = 60.02 g/mol
<u>Step 3: Convert</u>
- [DA] Set up:
- [DA] Divide/Multiply [Cancel out units]:
<u>Step 4: Check</u>
<em>Follow sig fig rules and round. We are given 3 sig figs.</em>
12.3588 g N₂O₂ ≈ 12.4 g N₂O₂
Answer: C.
Explanation:
The rusting of Clara's bike in which iron changes to rust is a chemical change. In a chemical change: the process is not easily reversible.
Answer:
Choice B. The solid with hydrogen bonding.
Assumption: the molecules in the four choices are of similar sizes.
Explanation:
Molecules in a molecular solid are held intact with intermolecular forces. To melt the solid, it is necessary to overcome these forces. The stronger the intermolecular forces, the more energy will be required to overcome these attractions and melt the solid. That corresponds to a high melting point.
For molecules of similar sizes,
- The strength of hydrogen bonding will be stronger than the strength of dipole-dipole attractions.
- The strength of dipole-dipole attractions (also known as permanent dipole) will be stronger than the strength of the induced dipole attractions (also known as London Dispersion Forces.)
That is:
Strength of Hydrogen bond > Strength of Dipole-dipole attractions > Strength of Induced dipole attractions.
Accordingly,
Melting point due to Hydrogen bond > Melting point due to Dipole-dipole attractions > Melting point due to Induced Dipole attractions.
- Induced dipole is possible between all molecules.
- Dipole-dipole force is possible only between polar molecules.
- Hydrogen bonds are possible only in molecules that contain
atoms that are bonded directly to atoms of 
, 
, or 
.
As a result, induced dipoles are the only force possible between molecules of the solid in choice C. Assume that the molecules are of similar sizes, such that the strengths of induced dipole are similar for these molecules.
Melting point in choice B > Melting point in choice D > Melting point in choice A and C.
