C4 + 1.2 Chemical Equations

Question 1

What state symbol is used for solids

Answer 1

s

Question 2

What state symbol is used for gases

Answer 2

g

Question 3

What state symbol is used for liquids

Answer 3

l

Question 4

What state symbol is used for aqueous solutions

Answer 4

aq

Question 5

Match the reactants to the products
CH^4 + 2O^2.              2CO^2 + 3H^2O
C^2H^5OH + 3O^2.      CO^2
C^3H^8 + 5O^2.            CO^2 + 2H^2O
C + O^2.                      3CO^2 + 4H^2O

Answer 5

CH^4 + 2O^2 = CO^2 + 2H^2O
C^2H^5OH + 3O2 = 2CO^2 + 3H^2O
C^3H^8 + 5O^2. = 3CO^2 + 4H^2O
C + O^2. = CO^2

Question 6

Whats the word equation for water

Answer 6

Hydrogen + oxygen -> water

(Reactants). (Products)

Question 7

What the symbol equation for water

Answer 7

H^2 (g) + O^2(g) -> H^2O(l) - unbalanced

Question 8

What do chemical equations show

Answer 8

The reactants (substances you start with) and the products (new substances made) in a reaction

Question 9

When balancing a chemical equation …

Answer 9

You can NEVER change a chemical formula e.g
H^2(g) +O^2(g) -> H^2O(l) Unbalanced

2H^2(g) + O^2(g) -> 2H^2O(l) Balanced

Question 10

Why is it important that equations are balanced

Answer 10

Because atoms cannot be created or destroyed in a chemical reaction. This is the law of conservation of mass:

The total mass of products formed in a reaction is equal to the total mass of the reactants

Question 11

How are the masses of atoms compared

Answer 11

By measuring them relative to atoms of carbon-12

Question 12

How can you work out the relative formula mass of a compound

Answer 12

By adding up the relative atomic masses (top number on periodic table) of the elements in it, in the ratio shown by it’s formula

e.g h^2SO^4 = (1x2) +32 +(16x4) = 2 + 32 +64 =98

Al^2(SO^4)^3 = (27x2) +(32 x 3) + (16x12) =342

Question 13

What is a mole

Answer 13

One mole of any substance is its relative formula mass, in grams

Question 14

What is avogadro constant

Answer 14

The number of atoms, molecules, or ions in a mole. This is always the same: 6.02 x10^23 per mole

Question 15

How do you calculate moles

Answer 15

Number of moles = mass (g) / Mr (relative atomic mass)
OR rearanged
mass(g) = number of moles x Mr

e.g number of moles in 19.6g of H^2SO^4
= 19.6/98 = 0.20mol.

Mass of 7.5x10^-3 moles of Al^2(SO^4)^3
= (7.5 x 10^-3) x 342 = 2.6g(2sf)

Question 16

How do you calculate the percentage by mass of each element in a compound

Answer 16

e.g CO^2
Relative formula mass = 12+(2x16)=44
Percentage mass of C in CO^2 = 12/44 x 100 = 27.3%

Question 17

Add number in front of these compunds to make these equations balanced:
NH^3 + O^2 -> NO + H^2O
HNO^3 -> NO^2 + H^2O + O^2

Answer 17

4NH^3 + 5O^2 -> 4NO + 6H^2O

4HNO^3 -> 4NO^2 + 2H^2O + O^2

Question 18

What is the reactant that gets used up first in a reaction called?

Answer 18

Limiting reactant. This is the reactant which is NOT in excess

Question 19

What does the limiting reactant limit

Answer 19

The amount of product formed

Question 20

What mass of carbon dioxide is formed when 7.41 g of copper(II) carbonate decomposes on heating?
CuCO^3 -> CuO + CO^2

Answer 20

Moles CuCO^3 = 0.060mol

Mass CO^2 = 44x0.060 = 2.64g

Question 21

Hydrazine (N^2H^4) can be made by reacting ammonia with hydrogen peroxide. What mass of ammonia is needed to make 148g of hydrazine?

Answer 21

Moles N^2H^4 = 4.625 mol
Moles NH^3 = 2x4.625 = 9.25 mol
Mass NH^3 = 17 x 9.26 = 157g

Question 22

4.8g of Mg (24 Mr) reacting with 7.3 g of HCl (H=1Mr Cl = 35.5 Mr). Which is the limiting reactant
Mg(s) + 2HCl (aq) -> MgCl^2(aq) + H^2(g)

Answer 22

Find moles:
4.8/24 = 0.2mol. 7.3/(1+35.5) = 0.2mol

In reaction it is 2HCl so 0.2 x2 = 0.4 moles are needed.
HCl is the limiting reactant

Question 23

What is the equivalent measurement of:
1dm 
10dm
1dm^2 
1dm^3

Answer 23

1dm = 1/10m = 10cm
10dm=1m
1dm^2 =100cm^2
1dm^3 = 1000cm^3

Question 24

How to you calculate concentration (g/dm^3)

Answer 24

Amount of solute (g) / volume of solution (dm^3)

Question 25

How can you increase the concentration of an aqueous solution (2 ways)

Answer 25

Adding more solute and dissolving it in the same volume of its solution
OR / AND
evaporating off some of the water from the solution so you have the same mass of solute in a smaller volume of solution

Question 26

Why are some solutions more concentrated

Answer 26

A more concentrated solution has more solute in the same volume of solution than a less concentrated solution