Calculations involving masses

Question 1

What is empirical formula?

Answer 1

simplest whole number ratio of atoms or ions of each element in a substance

Question 2

What is molecular formula?

Answer 2

the actual number of atoms of each element in one molecule

Question 3

In what instance would you use molecular formulas and when would you use empirical formula

Answer 3

Molecular- simple molecule

Empirical- giant lattice structure

Question 4

What is relative formula mass?

Answer 4

The sum of the relative atomic masses of all the atoms or ions in its formula

Question 5

What are the cute lil letters for the relative formula mass and atomic masses

Answer 5

M(I)
A(I)
(the I’s are in subscripts with no brackets)

Question 6

How do you find the relative formula mass

Answer 6

Find the atomic masses of each of the elements in the compound and times it by however many atoms there are in the compound. Then add these values to get the relative formula mass.

Question 7

Where can you find the relative atomic mass?

Answer 7

In the periodic table (higher number in the element square

Question 8

How do you find the empirical formula?

Answer 8

Divide the mass given the question by the atomic masses of the elements. Then divide these answers into the smaller ones to find the simple ratio. Then the ratio is how many atoms are in the compound (e.g 1:2 = CaCl2)

Question 9

How do you find the molecular formula?

Answer 9

It is determined by its empirical mass and formula mass:
Formula mass/empirical formula. The answer is that many more times of each element in the empirical formula (e.g CH2O = C6H12O6)

Question 10

What is the law of conservation of mass?

Answer 10

the mass of the solution is equal to the mass of the solvent AND the mass of the solute- the overall mass of the substances doesn’t change

Question 11

How do you work out the concentration (gdm-3)

Answer 11

Mass of solute (g) / volume of solution in dm-3

Question 12

How do you convert to 1 dm3 (decimetre cubed) from cm3

Answer 12

1 litre (1000cm3) = 1dm3

Question 13

What is a closed system

Answer 13

Where no substances are added or removed

Question 14

How does a balanced equation show the law of conservation of mass?

Answer 14

the number of atoms doesn’t change and so the mass cannot change

Question 15

How do you work out the masses of reactants and products in a balanced equation?

Answer 15

• Write the balanced equation
• Calculate the relative formula masses of the substances asked in the question
• Calculate the ratio of the masses (by multiplying the relative formula masses by the balancing numbers)
• Work out the mass for 1g of reactant or product (you want the one you have the mass for from the question)
• Times or divide by the mass you were given to get the grams of both (one should be the same from the question)

Question 16

What is the Avogadro constant

Answer 16

6.02 x 10^23 particles

Question 17

What is the mass of one mole in a substance?

Answer 17

Relative atomic mass or relative formula mass in grams (eg atomic mass of magnesium is 24 so 1 mol of mag = 24g and contains 6.02 x 10^23 atoms)

Question 18

How do you calculate the number of moles of substance?

Answer 18

mass of substance (g) / relative atomic mass (Ar or Mr) or relative formula mass

Question 19

What is the limiting reactant?

Answer 19

The reactant that gets consumed first in a chemical reaction and therefore limits how much product can be formed.

Question 20

How do you figure out the limiting reactant?

Answer 20

check on active learn - page 77 (worked example - too complicated to put on a flashcard)

Question 21

What is stoichiometry?

Answer 21

Ratio of moles of each substance