1 Stochiometry

Question 1

What is the main difference between a compound and a mixture?

Question 2

What is the difference between a liquid (l) and an aqueous solution (aq)

Answer 2

Liquid is a pure element or compound such as water.

Aqueous solution refers to a substance (or solution) dissolved in water.

NaCl(aq) is a solution of sodium chloride in water.

Question 3

A change from gas to solid is called…

Question 4

A change from solid to gas is called

Question 5

The difference between evaporation and boiling is, that…

Answer 5

… boiling happens at the boiling point

… evaporation happens between the melting point and the boiling point.

Question 6

Calculate the molar mass of

C₆H₁₂O₆

Answer 6

6(12.01) + 12(1.01) + 6(16.00)

= 180.18 g mol^-1

Question 7

Calculate the molar mass of

(NH₄)₂SO₄

Answer 7

2(14.01) + 8(1.01) + 32.07 + 4(16.00)

= 180.18 g mol^-1

Question 8

What symbol and unit has the relative atomic mass.

Answer 8

(Ar) - no unit

Relative atomic mass or atomic weight is a dimensionless physical quantity defined as the ratio of the average mass of atoms of a chemical element in a given sample to one unified atomic mass unit.

The unified atomic mass unit is defined as being ​1⁄12 of the atomic mass of a carbon-12 atom.

Question 9

Molecules have relative ….. masses.

Ionic compounds have relative ….. masses.

Answer 9

Molecules have relative molecurar masses.

Ionic compounds have relative formular masses.

Abbreviation: M_r

No unit, dimensionless

Question 10

0.100 mol of (NH₄)₂SO₄

represents :

a. ____ mol of ammonium ions
b. ____ hydrogen atoms
c. ______ atoms in total

Answer 10

a. 0.100 x 2 = 0.200 mol of ammonium ions (NH₄)
b. 0.100 x (4x2) x 6.02 x 10²³ hydrogen atoms
c. 0.100 x 15 x 6.02 x 10²³ atoms

Question 11

What mass of sodium chloride is produced when chlorine reacts with 52.60 g of sodium Iodide?

Question 12

Calculate the amount (in mol) in

this 8.80 g of carbon dioxide, CO₂

Answer 12

0.200 mol

Question 13

You shall find the number of a specific atoms in a substance which mass is given in kg?

What are the steps to calculate it?

Answer 13

1. Convert the mass of the substance into grams (g).
2. Calculate the amount of substance in mol, considering all atoms and using the formular n = m (g) / molar mass
3. Consider the number of specific atoms in the substance (for instance H₂O has 2 Hydrogen atoms) and mulitply by the molar to have number of atoms in mole
4. Multiply with the Avogadro constant of 6.02 x 10²³ to get the number of atoms.