C4

Question 1

What is relative formula mass symbol

Answer 1

Mr (r below m)

Question 2

How do you find the relative formula mass of a compound

Answer 2

Add together relative atomic mass (number above symbol) of each element

Question 3

Find the relative atomic mass of MgCl2

Answer 3

Mg + 2xCl = 24 + 2x35.5 = 95
So Mr of MgCl2 = 95

Question 4

Why is mass always conserved in chemical reactions

Answer 4

Because no atoms are destroyed or created meaning there are the same number and types of atom of each side of a reaction equations

Question 5

Explation of why you might observe a change in mass of an unsealed reaction vessel

Answer 5

If the mass increases, its probaly because of one of the reactants being a gas thats found in air. Before the reaction, the gas is floating in the air but its not contained in the reaction vessel so you can’t account for it’s mass. When the gas reacts to form part of the product, it becomes contained inside the reaction vessel meaning the total mass of the stuff inside the reaction vessel increases.

Question 6

What is a reaction vessel

Answer 6

Reaction vessels are any vessels in which chemical reactants can be contained for a reaction to take place and under the needed physical conditions.

Question 7

Why would a mass decrease?

Answer 7

Because one of the reactants is a gass and the other reactants are solids liquids or aqueous. If the vessel isn’t closed when reacting then the gas can escape meaning the products will loose mass

Question 8

How to find the mass conserved in a reaction

Answer 8

Amount of element x relative formula mass (top number) added with other elements.

Question 9

What is concentration

Answer 9

The amount of a substance (mass or number of moles) in a certain volume of a solution

Question 10

The more concentration means the

Answer 10

More solute there is in a given volume

Question 11

What is concentration measured in

Answer 11

G/dm cubed

Question 12

Equation for concentration

Answer 12

Mass (g) / volume of solvent (dm cubed)

Question 13

What is the concentration in g/dm cubed of a solution of sodium chloride where 30g of sodium chloride is disolved in 0.2 dm cubed of water

Answer 13

Concentration = 30/0.2 = 150 g/dm cubed

Question 14

Steps on how to do the reacting mass calculations

Answer 14

• tick the balanced equation
• ? The unbalaced equation
• find moles of ticked = mass /mr
• find moles of ?
• find mass of ? = moles x mr

Question 15

Mole:

Answer 15

A mole of any substance always contains the same number of atoms, molecules and ions

Question 16

Moles from masses equation:

Answer 16

Number of moles = mass/Ar or mass/Mr

Question 17

Masses from moles equation:

Answer 17

Mass (g) = number of moles x Ar

Question 18

How are masses of atoms compared?

Answer 18

They are compared by measuring them relative to atoms of carbon 12

Question 19

Why are chemical equations useful?

Answer 19

-for finding out how much of each substance is involved in a chemical reaction (use balanced symbol equation)

Question 20

Limiting reactants

Answer 20

The reactant that gets used up first in a reaction
(NOT THE ONE IN EXCESS)

Question 21

Example of limiting reactants:

Answer 21

-add dilute hydroclhloric acid to magnesium ribbon,
-hydrogen gas is given off and you see bubbles rise from magnesium until in excess

-the reason the reaction stops is that all the acid has been used up so the hydrocloric acid is the limiting reactant

Question 22

How can you work out the limiting reactant?

Answer 22

From a balanced equation if you know the number of moles of reactants before you start